Tuberculosis (TB) is caused by the intracellular bacteria Mycobacterium tuberculosis, and kills more than 1.5 million people every year worldwide. Immunity to TB is associated with the accumulation of IFNγ-producing T helper cell type 1 (Th1) in the lungs, activation of M.tuberculosis-infected macrophages and control of bacterial growth. However, very little is known regarding the early immune responses that mediate accumulation of activated Th1 cells in the M.tuberculosis-infected lungs. To define the induction of early immune mediators in the M.tuberculosis-infected lung, we performed mRNA profiling studies and characterized immune cells in M.tuberculosis-infected lungs at early stages of infection in the mouse model. Our data show that induction of mRNAs involved in the recognition of pathogens, expression of inflammatory cytokines, activation of APCs and generation of Th1 responses occurs between day 15 and day 21 post infection. The induction of these mRNAs coincides with cellular accumulation of Th1 cells and activation of myeloid cells in M.tuberculosis-infected lungs. Strikingly, we show the induction of mRNAs associated with Gr1+ cells, namely neutrophils and inflammatory monocytes, takes place on day 12 and coincides with cellular accumulation of Gr1+ cells in M.tuberculosis-infected lungs. Interestingly, in vivo depletion of Gr1+ neutrophils between days 10–15 results in decreased accumulation of Th1 cells on day 21 in M.tuberculosis-infected lungs without impacting overall protective outcomes. These data suggest that the recruitment of Gr1+ neutrophils is an early event that leads to production of chemokines that regulate the accumulation of Th1 cells in the M.tuberculosis-infected lungs.
Citation: Kang DD, Lin Y, Moreno J-R, Randall TD, Khader SA (2011) Profiling Early Lung Immune Responses in the Mouse Model of Tuberculosis. PLoS ONE 6(1): e16161. doi:10.1371/journal.pone.0016161
Editor: Samithamby Jeyaseelan, Louisiana State University, United States of America
Received: August 17, 2010; Accepted: December 8, 2010; Published: January 13, 2011
Copyright: © 2011 Kang et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Funding: This work was supported by 1K99/R00AI075106-01, R21AI083541 and Children's Hospital of Pittsburgh to SAK; HL69409 and AI072689 to TDR and a Research Advisory Committee Grant from Children's Hospital of Pittsburgh of the University of Pittsburgh Medical Center Health System to YL. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing interests: The authors have declared that no competing interests exist.
Tuberculosis (TB), caused by the intracellular bacteria Mycobacterium tuberculosis, is a global disease that kills more than 1.5 million people every year worldwide. Approximately one-third of the world's population is infected with M.tuberculosis and about 5–10% of these individuals will develop clinical disease over their lifetime . In addition, development of drug-resistant strains of M.tuberculosis and increased incidence of HIV-associated TB threatens to overwhelm the current measures for TB control . The only vaccine available against TB is BCG, which has variable efficacy in different populations. Thus, there is an urgent need to develop more effective vaccines against TB . However, a significant hurdle in design of new vaccines is the limited understanding of the requirements for early immune responses to TB in the lung.
Immunity to TB is dependent on the accumulation of IFNγ-producing T helper cell type 1 (Th1) in the lungs, subsequent activation of M.tuberculosis-infected macrophages and control of bacteria . The cytokine IL-12, made up of IL-12p35 and IL-12p40 subunits is crucial for the induction of IFNγ in Th1 cells . Accordingly, humans and mice with mutations in the IL-12/Th1 pathway are more susceptible to mycobacterial infections , , . In the mouse model of tuberculosis, the adaptive T cell immune responses are detected in the lung between day 18 and day 21 , ,  and coincide with control of bacteria . However, very little is known regarding the immune events that occur prior to accumulation of Th1 cells in the M.tuberculosis-infected lungs.
To define the induction of early immune mediators in the M.tuberculosis-infected lung, we have carried out mRNA profiling and characterized immune cells in M.tuberculosis-infected lungs at early stages of infection. Our data show that induction of genes involved in pathogen recognition, expression of inflammatory cytokines and activation of APCs takes place between days (D) 15 and 21 in M.tuberculosis-infected lungs. Also, we show that induction of mRNAs related to the IL-12/Th1 and TNF-alpha (TNFα) pathways occurs between D15–D21 post infection and coincides with cellular accumulation of Th1 cells and activation of myeloid cells in M.tuberculosis-infected lungs. Strikingly, we show the induction of mRNAs associated with Gr1+ cells, namely neutrophils and inflammatory monocytes, takes place on D12, and precedes the induction of mRNAs associated with the IL-12/Th1 pathway. We further confirm that Gr1+ cells accumulate in M.tuberculosis-infected lungs on D12 and show that depletion of Gr1+ neutrophils between days 10–15 results in decreased accumulation of Th1 cells in the M.tuberculosis-infected lungs on D21. However, decreased Th1 responses did not impact activation of myeloid cells in M.tuberculosis-infected lungs or bacterial control. Together, our data suggest that the recruitment of Gr1+ cells occurs prior to the accumulation of Th1 cells in M.tuberculosis-infected lungs and may regulate Th1 immune responses, but does not change overall protective outcomes.
Materials and Methods
C57BL/6 (B6) mice were purchased from The Jackson Laboratory (Bar Harbor, ME). Experimental mice were age and sex matched and used between the ages of eight to ten weeks. All mice were used in accordance with University of Pittsburgh Institutional Animal Care and Use Committee guidelines and were approved under Protocol 0807913. All efforts were made to minimize suffering and pain as described in this approved protocol.
Experimental infection and Gr1 depletion
The H37Rv strain of M.tuberculosis was grown in Proskauer Beck medium containing 0.05% Tween 80 to mid-log phase and frozen in 1 ml aliquots at −70°C. For aerosol infections, subject animals were infected with ~100 bacteria using a Glas-Col (Terre Haute, IN) airborne infection system as described in detail . For depletion of Gr1+ neutrophils, mice were treated with 300 µg of Gr1 depleting antibody (Clone IA8, BioXcell) or isotype control antibody (BioXcell) every 48 hours. Bacterial burden was estimated by plating the lung homogenates on 7H11 agar plates.
RNA extraction and microarray analysis
RNA was extracted from M.tuberculosis-infected and control uninfected lungs as previously described . RNA samples were reverse transcribed to generate cDNA. cDNAs from uninfected (Control) and M.tuberculosis-infected lungs from each time point were hybridized to microarrays 45000 mouse probes representing 21308 genes. Expression values were normalized with GeneChip Robust Multiarray Average (GCRMA) . Both raw data and the expression data set have been submitted to the NCBI Gene Expression Omnibus repository (GEO) with accession number GSE23014. Rank Product  was used to detect differentially expressed genes and to calculate False Discovery Rate (FDR). Rank Product was reported to perform well in small sample sizes and highly noise data set . All analyses were performed with R and Bioconductor . Functional Analysis using Gene Ontology terms for biological processes was performed with DAVID (http://david.abcc.ncifcrf.gov). Ingenuity Systems Pathway Analysis (http://www.ingenuity.com) was used for pathway analysis.
Cell Preparation and flow cytometry.
Lung cell suspensions were prepared as described before  and used for flow cytometric analyses. Briefly, a single cell suspension was prepared from either digested lung tissue by dispersing the tissue through a 70µm nylon tissue strainer (BD Falcon, Bedford, MA). The resultant suspension was treated with Gey's solution to remove any residual red blood cells, washed twice and counted. Single cell suspensions were then stained with fluorochrome-labeled antibodies specific for CD3 (17A2), CD4 (RM4-5), Gr1 (RB6-8C5), CD11b (M1/70), CD11c (HL3), and MHC class II I-Ab (AF6-120.1), CD44 (IM7). For intracellular cytokine detection, cells were stimulated with Phorbol myristate acetate (50 ng/ml), ionomycin (750 ng/ml; Sigma Aldrich) and Golgistop (BD Pharmingen), were surface stained, permeabilized with Cytofix-Cytoperm solution (BD Pharmingen) and stained with anti-IFNγ antibody (XMG1.2). Cells were collected on a Becton Dickinson LSRII flow cytometer using FACS Diva software. For analysis, FlowJo (Tree Star Inc, CA) was used for cell analysis. Differences between the means of experimental groups were analyzed using the two tailed Student's t-test. Differences were considered significant when p≤0.05.
Morphometric analysis and immunofluorescence
The lower right lobe of each lung was inflated with 10% neutral buffered formalin and processed routinely for light microscopy by hematoxylin and eosin stain (Colorado Histoprep, Fort Collins, CO). For immunofluorescence, paraffin was removed from the formalin-fixed lung sections, which were then washed with xylene, alcohol and PBS. Antigens were unmasked using a DakoCytomation Target Retrieval Solution and were blocked with 5% (v/v) normal donkey serum and Fc block. Endogenous biotin was neutralized with avidin followed by biotin (Sigma Aldrich). Sections were probed with goat anti mouse CD3ε to detect CD3 lymphocytes (clone M-20; Santa Cruz Biotechnology), and biotinylated Gr1 to detect neutrophils (Rat, BD Pharmingen) in the inflammatory lesions. Primary antibodies were detected with secondary antibody conjugated to Alexa flour 568 for CD3 (Alexa fluor 568, Donkey anti goat; Invitrogen). Gr1+ cells were visualized by adding Alexa fluor-488 and Streptavidin-alexa fluor 488 (Invitrogen). Slow fade gold antifade with DAPI (Molecular probes, Eugene, OR) was used to counterstain tissues and to detect nuclei. Images were obtained with a Zeiss Axioplan 2 microscope and were recorded with a Zeiss AxioCam digital camera.
Global changes of gene expression during the early stages of M.tuberculosis infection
Gonzalez-Juarrero et al. have studied the gene expression of M.tuberculosis-infected lungs during the chronic phase of infection . However, since accumulation of antigen-specific T cells and control of bacteria in the mouse model of tuberculosis takes place between days 15–20 post infection, we determined the global transcriptional responses in the lungs during the early immune response following M.tuberculosis infection. To address this, C57BL6 (B6) mice were aerosol-infected with ~100 CFU of M.tuberculosis and cDNA microarray hybridization was used to study gene expression profiles on infected lung cDNA at different time points during the early immune response. For each time point, cDNA from uninfected and M.tuberculosis-infected lungs were hybridized to microarrays containing 45000 mouse probes representing 21308 genes. Upon comparison to mRNA from uninfected lungs, 509 mRNAs from M.tuberculosis-infected lungs were differentially expressed at day 12 (D12), 371 mRNAs on day 15 (D15) and 1620 mRNAs on day 21 (D21) post infection (Figure 1a). Not surprisingly, many of the same mRNAs were differentially expressed at multiple time points. For example, 204 mRNAs were similarly induced or repressed on D12 and D15, 272 mRNAs on D15 and D21 and 195 mRNAs on D21 and D12. Also, 144 mRNAs were similarly induced or repressed at all three time points. Approximately half of the differentially regulated transcripts were induced (Figure 1b), whereas half were repressed (Figure 1c) on D12 and D15. However, more genes were induced (Figure 1b) than repressed at D21 (Figure 1c).
Figure 1. Global changes of gene expression during the early stages of M.tuberculosis infection.
B6 mice were infected with ~100 CFU M.tuberculosis via the aerosol route and at specific times after infection, lung tissue was harvested and processed to extract RNA. cDNA microarray hybridization was used to study gene expression profiles on infected lung cDNA at day 12 (D12 n = 4), day 15 (D15 n = 4) or day 21 (D21 n = 5) post infection. For each time point, cDNA was hybridized from uninfected (n = 3) and M.tuberculosis-infected lungs to microarrays containing 45000 mouse probes representing 21308 genes. Total genes differentially regulated at day 12 (D12) compared to day 15 (D15) and day 21 (D21) post infection was determined after controlling FDR at the level of 0.05 by using the R package “RankProd”. (a). Genes upregulated (b) or repressed (c) are also shown.doi:10.1371/journal.pone.0016161.g001
We then determined whether transcripts in particular pathways were coordinately regulated using Ingenuity Signaling software. We found that most groups of transcripts associated with inflammation, dendritic cell maturation and T helper function showed significant alterations in expression only on D21 post infection (Figure 2). However, a group of mRNAs included those encoding the host heat shock proteins (Table 1) were induced at D12. Overall, these data suggest that there is a dynamic regulation of mRNA expression during the early stages of infection and that while many pathways are induced at later times after infection (D21), mRNAs belonging to the host heat shock proteins are induced early and likely contribute to stabilization of protein induced in response to infection-related stress.
Figure 2. Induction of key immune pathways in mouse model of M.tuberculosis infection take places on D21 post infection.
B6 mice were infected with ~100 CFU M.tuberculosis via the aerosol route and at specific times after infection, lung tissue was harvested and processed to extract RNA. cDNA microarray hybridization was used to study gene expression profiles on uninfected lungs (n = 3), M.tuberculosis-infected lung cDNA at day 12 (D12 n = 4), day 15 (D15 n = 4) or day 21 (D21 n = 5) post infection and ingenuity signaling software was used to assess the induction of genes mainly induced on D21. Pathways induced are shown. The threshold represents 0.05 B–H adjusted p-value which was calculated from hypergeometric distribution. Longer bar represents a larger proportion of genes were enriched in a specific pathway.doi:10.1371/journal.pone.0016161.g002
Table 1. Induction of genes associated with heat shock proteins during early M.tuberculosis infection.doi:10.1371/journal.pone.0016161.t001
Regulated expression of mRNAs involved in innate immune responses
The engagement of pathogen-associated molecular pattern receptors is important for the initiation of innate immune responses. Toll like receptors (TLRs) are key components of the innate immune responses during mycobacterial infections, since induction of inflammatory cytokines following M.tuberculosis infection requires signals from TLR2 , , TLR4  and cooperation between TLR2 and TLR9 . Amongst the TLR genes, we found that mRNA transcripts for TLR 1, 2, 12 and 13, were significantly induced at day 21 (Table 2), while induction of TLR4 or TLR9 was not detected on D21 post infection. CD14, a TLR-associated protein required for macrophage activation following M.tuberculosis infection  was induced at D21, but not earlier in the infected lung. These data suggest that different TLRs may be functioning at different phases during the early stages of M.tuberculosis infection.
Table 2. Induction of genes associated with innate host immune mechanisms during early M.tuberculosis infection.doi:10.1371/journal.pone.0016161.t002
We also observed the altered expression of other types of pathogen recognition receptors after M.tuberculosis infection. Interestingly, we found that the mRNA encoding DC-SIGN (CD209A), a molecule that mediates M.tuberculosis binding and internalization in human dendritic cells , was significantly downregulated in D21-infected lungs (Table 2). In contrast, we found that genes encoding C-type II lectins such as DECTIN-1 (CLEC7A), DECTIN-2 (CLEC4N) and Mincle (CLEC4E) were induced between D15 and D21 (Table 2), consistent with a role for DECTIN-1 in induction of inflammatory cytokines in macrophages following M.tuberculosis infection , . Furthermore, Mincle was recently identified as the receptor for mycobacterial cord factor Trehalose dimycolate, which is involved in the induction of proinflammatory responses in myeloid cells . Interestingly, the transcripts for C-type lectin MDL-1 (CLEC5A), which is mainly expressed by neutrophils and macrophages, were induced at D12 with considerable increase in their levels at D21 . Furthermore, we found there was increased expression of the transcripts encoding CD11b (Integrin alpha M-ITGAM) and CD11c (Integrin alpha X-ITGAX) in D21 M.tuberculosis-infected lung, but not at earlier time points (Table 2).
We also found that mRNAs encoding the matrix metalloprotease, MMP13, was induced in D21-infected lungs (Table 2). Additional matrix metalloproteases, such as MMP9 and MMP8, were however not significantly induced at D21 in the M.tuberculosis-infected lungs (Table 2), although transcripts for MMP9 was induced early at D12. These data are consistent with the fact that MMPs are required for macrophage recruitment and granuloma formation  and suggest that these proteins may be involved in tissue remodeling and inflammation during early tuberculosis.
Following infection with M.tuberculosis, innate cells produce inflammatory cytokines that define the outcome of an adaptive host immune response. The induction of T helper 1 (Th1) responses during M.tuberculosis infection is largely dependent on IL-12 . Accordingly, we found that mRNAs encoding IL-12p40 (IL12B) and its receptor IL-12RB1 were induced in D21 M.tuberculosis-infected lungs (Table 2). Furthermore, IL-6 plays a crucial role in driving T cell responses during tuberculosis , and we found a significant induction of IL-6 mRNA on day 21 post infection. In contrast, mRNAs encoding anti-inflammatory cytokines such as IL-4 and IL-10 were not induced in the M.tuberculosis-infected lung (Table 2). These data suggest that induction of mRNAs involved in the initiation of Th1 adaptive immunity takes place between D15 and D21 in the M.tuberculosis-infected lungs. Together, these data suggest that distinct molecular signatures of innate immunity are induced at different times during the early phases of M.tuberculosis infection and may function to activate downstream immune responses.
Expression of mRNAs involved in adaptive Immune responses
It is well known that the IFNγ-mediated activation of macrophages is critical for mycobacterial control . Accordingly, we detected the induction of transcripts for IFNγ at D15 with further upregulation of IFNγ mRNA levels at D21 (Table 3). We next determined whether there was a positive correlation between induction of IFNγ mRNA in the lung between days 15 and 21, and the induction of genes linked to the IFNγ pathway. As expected, we found a positive correlation using Pearson's product moment correlation test, which follows a t-distribution with n-2 degrees of freedom, and found that genes encoding IFNγ-associated GTPases such as IGTP, IIGP1 and interferon-inducible proteins (IF130, IF135, IF144, IF147) as well as interferon regulatory factors (IRF1, IRF5, IRF7, IRF8) followed the pattern of IFNγ induction (Table 3). Furthermore, we found that transcripts for STAT-1, a key transcription factor in the IFNγ responses, was significantly induced at D21 (Table 3). To further validate the gene expression profiles, we then experimentally addressed the timing of accumulation of CD4+ T cells expressing IFNγ in M.tuberculosis-infected lungs by flow cytometry. We found that the percentage and number of activated CD4+ T cells (CD3+CD4+CD44hi) (Figure 3 a,c) and activated CD4+ T cells that produce IFNγ (Figure 3 b,d) accumulated in the M.tuberculosis-infected lungs between D15 and D21. These data suggest that Th1 cell accumulation occurs between D15–D21 in the mouse model of tuberculosis.
Figure 3. Accumulation of activated IFNγ-producing T cells in the lungs occurs between D15 and D21 following M.tuberculosis infection.
B6 mice were infected with ~100 CFU M.tuberculosis via the aerosol route and at specific times after infection lymphocytes were isolated from the lung to determine the percentage of activated CD4+ T cells (CD3+ CD4+ CD44+) (a), percentage of activated CD4+ T cell producing IFNγ (b) or number of activated CD4+ T cells (CD3+ CD4+ CD44+) (c), or number of activated CD4+ T cell producing IFNγ (d) by flow cytometry. The lung bacterial burden was determined in M.tuberculosis-infected lungs by plating lung homogenates (e). The data points represent the mean (±SD) of values from four-five mice (a–e). *, p≤0.05, **, p≤0.005. ***, p≤0.0005 over Day 0 samples.doi:10.1371/journal.pone.0016161.g003
Table 3. Induction of genes associated with the IFNγ pathway during early M.tuberculosis infection.doi:10.1371/journal.pone.0016161.t003
Tumor Necrosis Factor-alpha (TNFα) is required for the formation of protective granulomas during tuberculosis . We found that TNFα mRNA was expressed at D21 but not earlier in the M.tuberculosis-infected lungs (Table 4). Genes associated with the TNFα pathway, such as Tumor necrosis factor alpha-induced protein 2 (TNFAIP2), tumor necrosis factor receptor superfamily member 1b (TNFRSF1B), Fas ligand (FASL) and lymphotoxin (LTB) were all induced at D21 and showed a positive correlation with TNFα expression (Table 4). These data suggest that mRNAs associated with adaptive immune responses, such as those in the TNFα and IFNγ pathways are induced between D15–D21 following M.tuberculosis infection and coincide with control of M.tuberculosis burden in the lungs of infected mice (Figure 3e).
Table 4. Induction of genes associated with the TNFα pathway during early M.tuberculosis infection.doi:10.1371/journal.pone.0016161.t004
Integrins CD11a and CD18 have been shown to be critical for recruitment of T cells to the lung and to confer host resistance following infection with aerosolized M.tuberculosis . Accordingly, we found induction of transcripts encoding CD11a (ITGAL) and CD18 (ITGB2) on D21 in the M.tuberculosis infected lung (Table 5). Markers associated with T cells such as CD3 (CD3G, CD3D), CD8 (CD8A, CD8B1), CD4, and T cell activation molecules such as IL-7R and CD5 were also induced between D15 and D21 (Table 5). Interestingly, the induction of CD8 also coincided with the induction of granzymes (GZMA, GZMB, GZMK) (Table 5). Signaling lymphocyte activating molecule (SLAM) contributes to Th1 mediated immune responses to tuberculosis . We found that SLAM genes, such as SLAM 6 and 7, were exclusively induced at D21 and that SLAM 8 was induced on both D15 and D21. The cell surface glycoprotein 2B4 (CD244) is related to CD2 and is implicated in the regulation of NK- and T-cell function  and it was expressed on D21, but not earlier during infection (Table 5). Furthermore, we also found that the invariant TCR zeta chain (CD247), a member of the CD3 complex which is associated with the clonotypic alpha/beta TCR hetrodimer is also induced in the M.tuberculosis-infected lungs at D15 and D21. It has been reported that Lymphocyte antigen 6 complex, locus I (LY6I), a maturation marker for T and B lymphocytes  is induced during murine tuberculosis , and we show that transcripts encoding LY6I is induced during the early immune response on D15, with progressively more induction of D21 (Table 5).
Table 5. Induction of genes associated with the adaptive immune responses during early M.tuberculosis infection.doi:10.1371/journal.pone.0016161.t005
Fc Gamma (FcG) receptors are important for the effector functions of antibodies and modulating immune responses . In immune responses to M.tuberculosis, the absence of inhibitory receptor, FcGRIIb (encoding for FcG2B) during M.tuberculosis infection results in reduced bacterial burdens and decreased pathology, while absence of both inhibitory and stimulatory FcG receptors results in increased susceptibility and is associated with immunopathology . We found that FcgRI (FCGR1) is induced in the lung at D12 and its expression was further upregulated at D15 and D21, while other FcG receptors such as FcGrIIB (FCGR2B), FcGrIII (FCGR3) and FcGrIV (FCGR4) are induced at D21 (Table 5). These data suggest that both inhibitory and stimulatory FcG receptors are induced in the lung during the early immune response following M.tuberculosis infection.
Expression of mRNAs involved in host defense mechanisms
Our data suggest that in the low dose mouse tuberculosis infection model, IFNγ mRNA is induced between D15 and D21 (Table 3), which coincides with the accumulation of activated IFNγ-producing T cells (Figure 3). IFNγ-mediated activation of macrophages and production of effector molecules, such as inducible nitric oxide synthase (NOS2) and the phagocyte oxidase (PHOX), are the major sources of reactive intermediates that are required for macrophage killing of M.tuberculosis , . Interestingly, we found that transcripts encoding phagocyte oxidases (NCF1, NCF-2 and NCF4) were much more highly induced at D21 compared to NOS-2 mRNA transcripts (Table 6). In addition, mRNAs belonging to the MHC Class II pathway, such as MHC Class II transactivator (CIITA), which is the key molecule for MHC Class II expression , were also induced at D21 post infection (Table 6). Cellular analysis of M.tuberculosis-infected lung suspensions confirmed that upregulation of MHC Class II expression on lung DCs and lung macrophages occurs on D21 (Figure 4a,b). Mice lacking LRG-47 fail to control M.tuberculosis infection due to an iNOS-independent defect in maturation of M.tuberculosis-containing phagosomes  and we found that induction of the (p47) guanosine triphosphatase family, LRG-47 (IRGM1) occurs between D15 and D21 in the M.tuberculosis-infected lungs (Table 6), suggesting that control of mycobacteria is taking place during this specific stage of infection. Furthermore, induction of LRG-47 is IFNγ-dependent  and is consistent with the arrival of activated cytokine producing cells in the infected lung (Figure 3) and timing of upregulation of MHC Class II surface expression on myeloid cells (Figure 4) on D21.
Figure 4. Upregulation of MHC Class II expression on lung myeloid cells occurs on D21 following M.tuberculosis infection.
B6 mice were infected with ~100 CFU M.tuberculosis via the aerosol route and at specific times after infection, cells were isolated from the lung to determine the expression of MHC Class II expression on lung DCs (a) or lung macrophages (b) by flow cytometry. The mean fluorescent intensity (MFI) of MHC Class II expression is shown. The data points represent the mean (±SD) of values from four-five mice (a, b). **, p≤0.005. ***, p≤0.0005 over Day 0 samples.doi:10.1371/journal.pone.0016161.g004
Table 6. Induction of genes associated with host defense mechanisms during early M.tuberculosis infection.doi:10.1371/journal.pone.0016161.t006
Recently, arginase has been shown to be induced during M.tuberculosis infection and provides an advantage to the pathogen by suppression of nitric oxide . Accordingly, we found ARG1 and ARG2 mRNAs were induced in D21-infected lungs (Table 6). Furthermore, to survive in the hostile host environment generated in the granulomas, M.tuberculosis can acquire iron through lactotransferrin . Consistent with this survival strategy of M.tuberculosis, lactoferrin (LTF) was induced in M.tuberculosis-infected lungs at D21.
A growing body of evidence supports the hypothesis that specialized subsets of dendritic cells expressing indoleamine 2,3 dioxygenase (IDO1-INDO), which catalyzes oxidative catabolism of tryptophan have profound effects on T cell proliferation, differentiation, effector functions, and viability . Further, it was found that TB patients expressed high levels of INDO, which following anti-TB treatment, declined to levels detected in controls . We found that INDO mRNA was induced early at D15 and to higher levels at D21 (Table 6). In addition, genes favoring Mycobacterial survival such as LAPTM5 (lysosomal-associated protein transmembrane), CD68 (macrosial lysosoamyl glycoprotein) and CD53 (membrane late endosomes) and RAB32 protein ,  were induced at D21-M.tuberculosis-infected lungs (Table 6). Programmed death 1 (PD-1), an activation-induced inhibitory receptor is expressed on lymphocytes and monocytes and binds to their ligands, PD-L1 and PD-L2 downregulating T cell responses , specifically they can impact T cell proliferation and cytokine production during M.tuberculosis infection . Strikingly, PD-L1 (CD274) and PD-L2 (PGCD1LG2) were both induced on D21 in the M.tuberculosis-infected lungs (Table 6). This suggests that M.tuberculosis can actively promote down-modulatory mediators to counteract Th1-type and innate immunity as an immunopathological strategy.
Gr1+ cells accumulate prior to accumulation of IFNγ-producing cells during murine tuberculosis
Neutrophils are one of the major effector cells of innate immunity since they can recognize, phagocytose and kill microorganisms using effector mechanisms that involve secretion of reactive oxygen species and cytotoxic components. One of the most striking patterns of gene expression that was induced early in D12-M.tuberculosis-infected lungs was associated with genes involved in neutrophil recruitment and genes expressed by neutrophils. For example, genes that encode for CXC-chemokines such as CXCL1 (Gro-α), CXCL5 (Ena-78) and CXCL9 (MIG) were significantly induced at D12 and were induced to higher levels on D15 and D21 post infection (Table 7). CXCL1 is expressed in neutrophils following stimulation with M.tuberculosis . Furthermore, both CXCL1 and CXCL5 can also act as potent chemoattractants for neutrophils . Interestingly, both CXCL1 and CXCL5 are induced in response to IL-1β stimulation ,  and IL-1β can also induce neutrophil attraction , . Consistent with this role for IL-1β, we found significant induction of IL-1β in D12-M.tuberculosis-infected lungs. Expression of IL-1β is critical for host immunity to M.tuberculosis, since mice that lack IL-1β are highly susceptible to infection and succumb in the first 40 days following infection . These findings suggest that induction of IL-1β and chemokines CXCL1, CXCL5 and CXCL9 take place early during murine tuberculosis infection and may promote early recruitment of neutrophils to the M.tuberculosis-infected lungs.
Table 7. Induction of genes associated with early recruitment of neutrophil and monocyte during M.tuberculosis infection.doi:10.1371/journal.pone.0016161.t007
Serum amyloid proteins are induced during tissue injury, infection and inflammation and are detected during murine tuberculosis  and in human tuberculosis patients . Furthermore, addition of purified amyloid proteins to alveolar macrophages can enhance killing of M.tuberculosis in vitro . Strikingly, we found significant induction of transcripts encoding Serum amyloid protein 3 (SAA3) in the D12 M.tuberculosis-infected lungs (Table 7). Furthermore, IL-1β can induce SAA3 induction  and serum amyloid proteins which can in turn mediate priming of neutrophils via induction of reactive oxygen species , . S100A8 and S100A9 are small calcium-binding proteins that are expressed in tuberculosis patients  and produced by activated neutrophils and monocytes. Our data show that both S100A8 and S100A9 are induced in the D12-M.tuberculosis-infected lungs (Table 7). Importantly, S100A8, S100A9, and S100A8/A9 have each been shown to induce neutrophil chemotaxis , . Furthermore, IL-1β is known to be a potent inducer of S100 proteins . These data suggest that induction of genes encoding serum amyloid proteins and S100 proteins on D12 correlates with expression of other neutrophil-associated genes early in M.tuberculosis-infected lungs.
In addition to early induction of CXC chemokines, we also show that induction of genes encoding C-C chemokines namely CCL-2 (MCP-1), CCL8 (MCP-2), CCL12 (MCP-5) and CCL22 (MDC) occurs on D12 and progressively increases between D15 and D21 post infection (Table 7). The C-C-chemokines are small molecular weight chemotactic proteins that play an important role in neutrophil recruitment during inflammatory conditions  and in macrophage/monocyte recruitment during M.tuberculosis infection . These data suggest that early induction of genes associated with monocyte and neutrophilic recruitment takes place on D12 in the M.tuberculosis-infected lungs.
Our data suggest that genes associated with neutrophil and monocyte recruitment and activation are induced prior to induction of genes belonging to the adaptive immune response. Gr1 (Ly6G/Ly6C) is a marker that is expressed on both neutrophils as well as on a population of inflammatory monocytes , , . For this reason, we experimentally determined the timing of accumulation of Gr1+ neutrophilic population (CD11b+ Gr1+) (Figure 5a)  and Gr1+ monocytic population (CD11b− Gr1+ F4/80+) (Figure 5b) , ,  in the M.tuberculosis-infected lungs. Consistent with our gene expression profiles, we found that Gr1+ neutrophilic and monocytic accumulation in the M.tuberculosis-infected lungs occurred at day 12 post infection (Figure 5a). While neutrophils were continuously recruited until D21, the accumulation of monocytes in the infected lungs was transient. Histologically, we observed an increased accumulation of Gr1+ cells around blood vessels on D12 and D15, while Gr1+ cells were observed in the lung interstitium by D21 (Figure 5c). These data experimentally support our gene expression analyses that early neutrophilic and monocytic responses precede the accumulation of activated T cells in the M.tuberculosis-infected lung.
Figure 5. Early recruitment of Gr1+ cells occurs on D12 and precedes accumulation of activated T cells.
B6 mice were infected with ~100 CFU M.tuberculosis via the aerosol route and at specific times after infection, cells were isolated from the lung and the percentage of Gr1+ neutrophils (a) or Gr1+ monocytes (b) were determined by flow cytometry. In some B6 M.tuberculosis-infected mice, lungs were fixed in 10% formalin, embedded in paraffin and the accumulation of Gr1+ cells (green) and CD3+ T cells (red) determined by immunofluorescence (c). The data points represent the mean (±SD) of values from four-five mice (a,b). *, p≤0.05, **, p≤0.005. ***, p≤0.0005 over Day 0 samples.doi:10.1371/journal.pone.0016161.g005
Depletion of Gr1+ cells during the early immune response results in reduced Th1 responses
Given that our data suggesting that neutrophils and monocytes accumulate prior to activated T cells in the lung, we next addressed whether the early accumulation of Gr1+ neutrophils had an effect on host adaptive immune responses. To do this, we specifically depleted Gr1+ neutrophils using a monoclonal antibody (Clone 1A8), which is known to specifically deplete neutrophils without impacting Gr1+ monocyte populations . We treated M.tuberculosis-infected mice with 1A8 antibody or isotype control antibody every 48 hours between D10–D15 post infection and this resulted in significant depletion of Gr1+ neutrophils in the lungs of Mtb-infected mice on D15 (Figure 6a). However, by D21 we could detect Gr1+ neutrophils, albeit at reduced frequency when compared to isotype-control treated mice (Figure 6b). Interestingly, depletion of Gr1+ neutrophils between D10–15 did not impact accumulation of total CD4+ T cells in the lungs (Figure 7a), but resulted in decreased accumulation of activated CD4+ cells (Figure 7b) and decreased percentage and number of IFNγ-producing T cells in the M.tuberculosis-infected lung on D21 (Figure 7c–d). Also, the reduced number of IFNγ-producing CD4+ T cells coincided with reduced expression of CXCL9 mRNA expression in the lung (Figure 7e). However, reduced number of IFNγ-producing cells did not have an adverse impact on activation of lung dendritic cells (Figure 7f), lung macrophages (Figure 7g) and lung bacterial burden (Figure 7h), since the MHC Class II upregulation and bacterial burden was comparable in control isotype-treated and Gr1-depleted M.tuberculosis-infected mice. Further, we did not find any differences histologically in granuloma formation (data not shown). These data suggest that the early recruitment of Gr1+ cells during M.tuberculosis infection plays a role in regulating the quality of adaptive CD4+ Th1 immune responses by modulating chemokine expression but does not impact overall protective outcomes.
Figure 6. Treatment with Gr1+ depleting antibody results in significant decrease in lung neutrophils.
B6 mice were infected with ~100 CFU M.tuberculosis via the aerosol route and treated with either isotype control antibody (Isotype) or Gr1 depleting antibody between days 10–15 (D10–D15) post infection. Cells were isolated from antibody treated M.tuberculosis-infected mice and the percentage of lung neutrophils were determined on day 15 (a) or day 21(b) by flow cytometry. The data points represent the mean (±SD) of values from five mice (a–b) ***, p≤0.0005 over isotype control treated M.tuberculosis-infected samples.doi:10.1371/journal.pone.0016161.g006
Figure 7. Depletion of Gr1+ cells between day 10–15 results in reduced Th1 responses but not impaired myeloid cell activation.
B6 mice were infected with ~100 CFU M.tuberculosis via the aerosol route and treated with either isotype control antibody (Isotype) or Gr1 depleting antibody between days 10–15 (D10–D15) post infection. Lung cells were isolated from antibody treated M.tuberculosis-infected mice and the number of total CD4+ CD3+ cells (a), number of activated CD4+ cells (b), percentage of activated IFNγ-producing cells (c), number of CD4+ CD44+ IFNγ-producing cells (d) was determined by flow cytometry. mRNA expression of CXCL9 in lungs of M.tuberculosis-infected isotype control mice or neutrophil-depleted mice was determined by RT-PCR (e). MHC Class II expression on lung DCs (f) and MHC Class II expression on lung macrophages (g) was determined in lungs of M.tuberculosis-infected isotype control treated mice or neutrophil-depleted mice by flow cytometry. The mean fluorescent intensity (MFI) of MHC Class II expression is shown. Lung bacterial burden from antibody-treated mice was determined by plating lung homogenates on D21 post infection (h). The data points represent the mean (±SD) of values from four-five mice (a–h). *, p≤0.05**, p≤0.005. ***, p≤0.0005 over isotype control treated M.tuberculosis-infected samples. ns-not significant.doi:10.1371/journal.pone.0016161.g007
A previous study analyzed the host immune response to M.tuberculosis infection and the progression to chronic TB infection using whole genome microarrays . However, not much is known about the kinetics of the early host immune responses induced in the lung following M.tuberculosis infection. Using a low dose model of M.tuberculosis murine infection, we have comprehensively studied the early immune responses in the M.tuberculosis-infected lung. Our data show that mRNAs involved with heat shock proteins are amongst one of the first transcripts induced in the lung in response to M.tuberculosis infection. Interestingly, the host heat shock protein mRNA induction is transient and it is not maintained on D15. Furthermore, we also show that majority of the mRNAs encoding proteins that are involved in initiation of innate immune responses, such as Toll-like receptors and C-type lectins, were induced between D15 and D21. This pattern correlated with induction of mRNAs associated with generation of adaptive immune responses, such as markers from cells from the adaptive immune system and genes associated with production of effector cytokines. The induction of these mRNAs coincides with cellular accumulation of activated T cells that can produce IFNγ and activation of lung myeloid cells in the M.tuberculosis-infected lung on D21. These findings are consistent with published studies, in which adoptively transferred M.tuberculosis-specific T cells undergo activation and accumulate in the infected lungs between days 15–20 , . Furthermore, we also show that accumulation of activated T cells in the lungs coincides with the induction of genes associated with host defense mechanisms such as PHOX and LRG-47, as well as genes associated with immunomodulatory functions such as arginase and INDO. These data suggest that there is a constant and dynamic regulation between host and pathogen factors that likely defines the final outcome of the infection.
One of the most intriguing questions in M.tuberculosis research is understanding what causes the delay in mounting an effective adaptive immune response, since accumulation of activated T cells does not occur until D15 in the M.tuberculosis-infected lungs. It has been proposed that it is likely that the slow growth of M.tuberculosis in the low dose aerosol challenge model results in limited availability of antigen, thereby resulting in a delay in antigen presentation and delayed accumulation of activated T cells in the lung , . This is consistent with our data that show that genes involved with antigen presentation and pathogen associated receptor recognition are induced between D15 and D21, but not earlier. Another likely possibility for the delay in induction of mRNAs involved in antigen-presentation and initiation of T cell priming may be due to bacterial subversion of host immune responses. With regard to this, it has been shown that M.tuberculosis can inhibit MHC Class II presentation ,  and it is possible that this results in delayed activation of antigen-presenting cells. Memory responses in previously infected mice  or in mice vaccinated with a M.tuberculosis vaccine , result in accumulation of activated T cells between D12 and D15 in the infected-lung. The small window of accelerated T cell memory responses results in enhanced control of bacterial burden and is reflected in 10 fold reduction in bacterial burden , . These studies suggest that accelerating the accumulation of activated T cells to the lung may result in better protection outcomes. Studying the early memory responses using comprehensive gene and cellular profiling as described in this study will enable us to identify pathways induced early and will allow us to overcome the limitations of current vaccines by enhancing these innate mechanism and accelerating the initiation of adaptive immune responses.
One of the important and novel findings of this study is that genes associated with neutrophilic and monocytic responses are induced between D12 and D15 and precede the induction of genes associated with the Th1 pathway. Also, our experimental data showing the accumulation of Gr1+ neutrophils and monocytes on D12 in the M.tuberculosis-infected lung validates our gene expression profiles. To our knowledge, this is the first study to experimentally show that the accumulation of Gr1+ neutrophils in the lungs takes place prior to accumulation of adaptive T cells. The role of neutrophils in protective immunity against M.tuberculosis is controversial. Although accumulation of neutrophils in bronchoalveolar spaces has been described in active human tuberculosis , it is not known whether neutrophils have direct bacteriocidal or immunologic functions. Some in vitro studies have shown that neutrophils have direct mycobacteriocidal effects , , while other studies have shown that neutrophils fail to generate oxidative burst upon phagocytosis of mycobacteria . In the mouse model of tuberculosis, depletion of neutrophils one day prior to infection did not impact overall susceptibility but had an effect on granuloma formation and resulted in delayed expression of CXCL9 . The receptor for CXCL9, CXCR3 is expressed on activated T cells that are recruited to the M.tuberculosis infected lung . Together, these data suggest that the early recruitment of Gr1+ neutrophils may play a role in regulating the adaptive T cell immunity during M.tuberculosis infection. This hypothesis is tested by depleting neutrophils between D10–15 and we show that this results in decreased expression of CXCL9 mRNA expression and reduced accumulation of Th1 cells in the M.tuberculosis-infected lung on D21. These data suggest that induction of neutrophil-associated chemokines such as CXCL9 and CXCL10 on D12–D15 may be key to accumulation of activated Th1 cells in the lung on D21. However, the decreased accumulation of Th1 cells on D21 did not impact overall myeloid cell activation or lung bacterial burden suggesting the Th1 response seen in neutrophil-depleted mice is likely sufficient to confer control of bacteria. Furthermore, we do not see any effects of neutrophil depletion in the pathology observed during the early phases in M.tuberculosis-infected lungs. These data suggest that the Th1 immune responses seen in isotype-treated M.tuberculosis-infected mice may in fact be excessive and may be contributing to the immunopathology associated with chronic TB during the later stages of infection. Based on these data, we are currently investigating whether the absence of early neutrophils has any effects on protective outcomes and pathology associated with chronic TB. This would shed further light on the detrimental (increased expression of CXCR3-ligating chemokines, Th1 recruitment and associated pathology) versus beneficial (optimal Th1 responses required for macrophage activation and mycobacterial control) effects of early neutrophil influx in TB pathogenesis.
Monocytes recruited to the site of infection can undergo differentiation into tissue macrophages or DCs. Recently a Gr1+ monocyte population was identified to be induced during inflammatory conditions and contributes to host resistance against pathogens , . Consistent with this, we have identified that Gr1+ F4/80+ monocyte population accumulates in the lung early following M.tuberculosis infection. Unlike the Gr1+ neutrophil population, our studies show the Gr1+ monocyte population increase is transient, suggesting that these inflammatory monocytes probably then undergo differentiation into DCs and macrophages and contribute to effector function.
In summary, our cellular and gene expression analyses demonstrate the early recruitment of neutrophils and monocytes to the lung following M.tuberculosis infection. Further, we show that the early neutrophilic recruitment and associated gene expression likely contributes to the accumulation of activated cytokine-producing Th1 cells on D21. Further studies on which neutrophil-associated chemokines are crucial for regulation of adaptive immunity and will allow us to define immunopathology versus protection during TB.
The authors thank Dr. John Alcorn, Dr. Radha Gopal and Samantha Slight, Children's Hospital of Pittsburgh for critical reading of the manuscript. We thank the Genomic Proteomics Core Laboratories of the University of Pittsburgh (supported by the Clinical and Translational Science Institute) and the Flow cytometry Core, Children's Hospital of Pittsburgh for technical expertise.
Conceived and designed the experiments: SAK TDR. Performed the experiments: DDK YL JRM. Analyzed the data: DDK YL JRM TDR SAK. Contributed reagents/materials/analysis tools: DDK TDR SAK. Wrote the paper: DDK TDR SAK.
- 1. Dye C, Scheele S, Dolin P, Pathania V, Raviglione M (1999) Global Burden of Tuberculosis. Estimated Incidence, Prevalence, and Mortality by Country. Journal of the American Medical Association 282: 677–686.
- 2. Koenig R (2008) Drug-resistant tuberculosis. In South Africa, XDR TB and HIV prove a deadly combination. Science 319: 894–897.
- 3. Flynn J, Chan J (2001) Immunology of tuberculosis. Annual Review of Immunology 19: 93–129.
- 4. Trinchieri G, Pflanz S, Kastelein R (2003) The IL-12 family of heterodimeric cytokines: new players in the regulation of T cell responses. Immunity 19: 641–644.
- 5. Cooper AM, Dalton DK, Stewart TA, Griffin JP, Russell DG, et al. (1993) Disseminated tuberculosis in interferon gamma gene-disrupted mice. Journal of Experimental Medicine 178: 2243–2247.
- 6. Flynn JL, Chan J, Triebold KJ, Dalton DK, Stewart TA, et al. (1993) An essential role for interferon gamma in resistance to Mycobacterium tuberculosis infection. Journal of Experimental Medicine 178: 2249–2254.
- 7. Casanova JL (2001) Mendelian susceptibility to mycobacterial infection in man. Swiss Med Wkly 131: 445–454.
- 8. Reiley WW, Calayag MD, Wittmer ST, Huntington JL, Pearl JE, et al. (2008) ESAT-6-specific CD4 T cell responses to aerosol Mycobacterium tuberculosis infection are initiated in the mediastinal lymph nodes. Proc Natl Acad Sci U S A 105: 10961–10966.
- 9. Cooper AM, Khader SA (2008) The role of cytokines in the initiation, expansion, and control of cellular immunity to tuberculosis. Immunol Rev 226: 191–204.
- 10. Khader SA, Rangel-Moreno J, Fountain JJ, Martino CA, Reiley WW, et al. (2009) In a murine tuberculosis model, the absence of homeostatic chemokines delays granuloma formation and protective immunity. J Immunol 183: 8004–8014.
- 11. Roberts A, Cooper A, Belisle J, Turner J, Gonzalez-Juarerro M, et al. (2002) Murine Models of Tuberculosis. In: Kaufmann S, Kabelitz D, editors. Methods in Microbiology. Second ed. London: Academic Press. pp. 433–462.
- 12. Khader SA, Pearl JE, Sakamoto K, Gilmartin L, Bell GK, et al. (2005) IL-23 compensates for the absence of IL-12p70 and is essential for the IL-17 response during tuberculosis but is dispensable for protection and antigen-specific IFN-gamma responses if IL-12p70 is available. J Immunol 175: 788–795.
- 13. Wu Z, Irizarry RA, Gentleman R, Martinez-Murillo F, Spencer F (2004) A Model-Based Background Adjustment for Oligonucleotide Expression Arrays. journal of the American Statistical Association 99: 909–917.
- 14. Breitling R, Armengaud P, Amtmann A, Herzyk P (2004) Rank products: a simple, yet powerful, new method to detect differentially regulated genes in replicated microarray experiments. FEBS Lett 573: 83–92.
- 15. Jeffery IB, Higgins DG, Culhane AC (2006) Comparison and evaluation of methods for generating differentially expressed gene lists from microarray data. BMC Bioinformatics 7: 359.
- 16. Gentleman RC, Carey VJ, Bates DM, Bolstad B, Dettling M, et al. (2004) Bioconductor: open software development for computational biology and bioinformatics. Genome Biol 5: R80.
- 17. Gonzalez-Juarrero M, Kingry LC, Ordway DJ, Henao-Tamayo M, Harton M, et al. (2009) Immune response to Mycobacterium tuberculosis and identification of molecular markers of disease. Am J Respir Cell Mol Biol 40: 398–409.
- 18. Underhill DM, Ozinsky A, Hajjar AM, Stevens A, Wilson CB, et al. (1999) The Toll-like receptor 2 is recruited to macrophage phagosomes and discriminates between pathogens. Nature 401: 811–815.
- 19. Kincaid EZ, Wolf AJ, Desvignes L, Mahapatra S, Crick DC, et al. (2007) Codominance of TLR2-dependent and TLR2-independent modulation of MHC class II in Mycobacterium tuberculosis infection in vivo. J Immunol 179: 3187–3195.
- 20. Pompei L, Jang S, Zamlynny B, Ravikumar S, McBride A, et al. (2007) Disparity in IL-12 release in dendritic cells and macrophages in response to Mycobacterium tuberculosis is due to use of distinct TLRs. J Immunol 178: 5192–5199.
- 21. Bafica A, Scanga C, Feng C, Leifer C, Cheever A, et al. (2005) TLR9 regulates Th1 responses and cooperates with TLR2 in mediating optimal resistance to Mycobacterium tuberculosis. Journal of Experimental Medicine 202: 1715–1724.
- 22. Bowdish DM, Sakamoto K, Kim MJ, Kroos M, Mukhopadhyay S, et al. (2009) MARCO, TLR2, and CD14 are required for macrophage cytokine responses to mycobacterial trehalose dimycolate and Mycobacterium tuberculosis. PLoS Pathog 5: e1000474.
- 23. Tailleux L, Schwartz O, Herrmann JL, Pivert E, Jackson M, et al. (2003) DC-SIGN is the major Mycobacterium tuberculosis receptor on human dendritic cells. J Exp Med 197: 121–127.
- 24. Rothfuchs AG, Bafica A, Feng CG, Egen JG, Williams DL, et al. (2007) Dectin-1 interaction with Mycobacterium tuberculosis leads to enhanced IL-12p40 production by splenic dendritic cells. J Immunol 179: 3463–3471.
- 25. Zenaro E, Donini M, Dusi S (2009) Induction of Th1/Th17 immune response by Mycobacterium tuberculosis: role of dectin-1, Mannose Receptor, and DC-SIGN. J Leukoc Biol 86: 1393–1401.
- 26. Ishikawa E, Ishikawa T, Morita YS, Toyonaga K, Yamada H, et al. (2009) Direct recognition of the mycobacterial glycolipid, trehalose dimycolate, by C-type lectin Mincle. J Exp Med 206: 2879–2888.
- 27. Aoki N, Kimura Y, Kimura S, Nagato T, Azumi M, et al. (2009) Expression and functional role of MDL-1 (CLEC5A) in mouse myeloid lineage cells. J Leukoc Biol 85: 508–517.
- 28. Taylor JL, Hattle JM, Dreitz SA, Troudt JM, Izzo LS, et al. (2006) Role for matrix metalloproteinase 9 in granuloma formation during pulmonary Mycobacterium tuberculosis infection. Infect Immun 74: 6135–6144.
- 29. Appelberg R, Castro AG, Pedrosa J, Minoprio P (1994) Role of interleukin-6 in the induction of protective T cells during mycobacterial infections in mice. Immunology 82: 361–364.
- 30. Saunders BM, Tran S, Ruuls S, Sedgwick JD, Briscoe H, et al. (2005) Transmembrane TNF is sufficient to initiate cell migration and granuloma formation and provide acute, but not long-term, control of Mycobacterium tuberculosis infection. J Immunol 174: 4852–4859.
- 31. Ghosh S, Chackerian AA, Parker CM, Ballantyne CM, Behar SM (2006) The LFA-1 adhesion molecule is required for protective immunity during pulmonary Mycobacterium tuberculosis infection. J Immunol 176: 4914–4922.
- 32. Pasquinelli V, Quiroga MF, Martinez GJ, Zorrilla LC, Musella RM, et al. (2004) Expression of signaling lymphocytic activation molecule-associated protein interrupts IFN-gamma production in human tuberculosis. J Immunol 172: 1177–1185.
- 33. Boles KS, Nakajima H, Colonna M, Chuang SS, Stepp SE, et al. (1999) Molecular characterization of a novel human natural killer cell receptor homologous to mouse 2B4. Tissue Antigens 54: 27–34.
- 34. Pflugh DL, Maher SE, Bothwell AL (2000) Ly-6I, a new member of the murine Ly-6 superfamily with a distinct pattern of expression. J Immunol 165: 313–321.
- 35. Ravetch JV, Bolland S (2001) IgG Fc receptors. Annu Rev Immunol 19: 275–290.
- 36. Maglione PJ, Xu J, Casadevall A, Chan J (2008) Fc gamma receptors regulate immune activation and susceptibility during Mycobacterium tuberculosis infection. J Immunol 180: 3329–3338.
- 37. Ehrt S, Schnappinger D, Bekiranov S, Drenkow J, Shi S, et al. (2001) Reprogramming of the macrophage transcriptome in response to interferon-gamma and Mycobacterium tuberculosis: signaling roles of nitric oxide synthase-2 and phagocyte oxidase. J Exp Med 194: 1123–1140.
- 38. Chang CH, Guerder S, Hong SC, van Ewijk W, Flavell RA (1996) Mice lacking the MHC class II transactivator (CIITA) show tissue-specific impairment of MHC class II expression. Immunity 4: 167–178.
- 39. MacMicking J, Taylor G, McKinney J (2003) Immune control of Tuberculosis by IFN-g-inducible LRG-47. Science 302: 654–659.
- 40. El Kasmi KC, Qualls JE, Pesce JT, Smith AM, Thompson RW, et al. (2008) Toll-like receptor-induced arginase 1 in macrophages thwarts effective immunity against intracellular pathogens. Nat Immunol 9: 1399–1406.
- 41. Olakanmi O, Schlesinger LS, Ahmed A, Britigan BE (2004) The nature of extracellular iron influences iron acquisition by Mycobacterium tuberculosis residing within human macrophages. Infect Immun 72: 2022–2028.
- 42. Mellor A (2005) Indoleamine 2,3 dioxygenase and regulation of T cell immunity. Biochem Biophys Res Commun 338: 20–24.
- 43. Almeida AS, Lago PM, Boechat N, Huard RC, Lazzarini LC, et al. (2009) Tuberculosis is associated with a down-modulatory lung immune response that impairs Th1-type immunity. J Immunol 183: 718–731.
- 44. Deretic V, Singh S, Master S, Harris J, Roberts E, et al. (2006) Mycobacterium tuberculosis inhibition of phagolysosome biogenesis and autophagy as a host defence mechanism. Cell Microbiol 8: 719–727.
- 45. Kyei GB, Vergne I, Chua J, Roberts E, Harris J, et al. (2006) Rab14 is critical for maintenance of Mycobacterium tuberculosis phagosome maturation arrest. Embo J 25: 5250–5259.
- 46. Freeman GJ, Long AJ, Iwai Y, Bourque K, Chernova T, et al. (2000) Engagement of the PD-1 immunoinhibitory receptor by a novel B7 family member leads to negative regulation of lymphocyte activation. J Exp Med 192: 1027–1034.
- 47. Jurado JO, Alvarez IB, Pasquinelli V, Martinez GJ, Quiroga MF, et al. (2008) Programmed death (PD)-1:PD-ligand 1/PD-ligand 2 pathway inhibits T cell effector functions during human tuberculosis. J Immunol 181: 116–125.
- 48. Riedel DD, Kaufmann SH (1997) Chemokine secretion by human polymorphonuclear granulocytes after stimulation with Mycobacterium tuberculosis and lipoarabinomannan. Infect Immun 65: 4620–4623.
- 49. Walz A, Burgener R, Car B, Baggiolini M, Kunkel SL, et al. (1991) Structure and neutrophil-activating properties of a novel inflammatory peptide (ENA-78) with homology to interleukin 8. J Exp Med 174: 1355–1362.
- 50. Chang MS, McNinch J, Basu R, Simonet S (1994) Cloning and characterization of the human neutrophil-activating peptide (ENA-78) gene. J Biol Chem 269: 25277–25282.
- 51. Oliveira SH, Canetti C, Ribeiro RA, Cunha FQ (2008) Neutrophil migration induced by IL-1beta depends upon LTB4 released by macrophages and upon TNF-alpha and IL-1beta released by mast cells. Inflammation 31: 36–46.
- 52. Calkins CM, Bensard DD, Shames BD, Pulido EJ, Abraham E, et al. (2002) IL-1 regulates in vivo C-X-C chemokine induction and neutrophil sequestration following endotoxemia. J Endotoxin Res 8: 59–67.
- 53. Mayer-Barber KD, Barber DL, Shenderov K, White SD, Wilson MS, et al. (2010) Caspase-1 independent IL-1beta production is critical for host resistance to mycobacterium tuberculosis and does not require TLR signaling in vivo. J Immunol 184: 3326–3330.
- 54. Singh PP, Kaur S (2006) Serum amyloid P-component in murine tuberculosis: induction kinetics and intramacrophage Mycobacterium tuberculosis growth inhibition in vitro. Microbes Infect 8: 541–551.
- 55. de Beer FC, Nel AE, Gie RP, Donald PR, Strachan AF (1984) Serum amyloid A protein and C-reactive protein levels in pulmonary tuberculosis: relationship to amyloidosis. Thorax 39: 196–200.
- 56. Sommer G, Weise S, Kralisch S, Scherer PE, Lossner U, et al. (2008) The adipokine SAA3 is induced by interleukin-1beta in mouse adipocytes. J Cell Biochem 104: 2241–2247.
- 57. Hatanaka E, Pereira Ribeiro F, Campa A (2003) The acute phase protein serum amyloid A primes neutrophils. FEMS Immunol Med Microbiol 38: 81–84.
- 58. Bjorkman L, Karlsson J, Karlsson A, Rabiet MJ, Boulay F, et al. (2008) Serum amyloid A mediates human neutrophil production of reactive oxygen species through a receptor independent of formyl peptide receptor like-1. J Leukoc Biol 83: 245–253.
- 59. Pechkovsky DV, Zalutskaya OM, Ivanov GI, Misuno NI (2000) Calprotectin (MRP8/14 protein complex) release during mycobacterial infection in vitro and in vivo. FEMS Immunol Med Microbiol 29: 27–33.
- 60. Ryckman C, Vandal K, Rouleau P, Talbot M, Tessier PA (2003) Proinflammatory activities of S100: proteins S100A8, S100A9, and S100A8/A9 induce neutrophil chemotaxis and adhesion. J Immunol 170: 3233–3242.
- 61. Vandal K, Rouleau P, Boivin A, Ryckman C, Talbot M, et al. (2003) Blockade of S100A8 and S100A9 suppresses neutrophil migration in response to lipopolysaccharide. J Immunol 171: 2602–2609.
- 62. Rahimi F, Hsu K, Endoh Y, Geczy CL (2005) FGF-2, IL-1beta and TGF-beta regulate fibroblast expression of S100A8. FEBS J 272: 2811–2827.
- 63. Maus UA, Waelsch K, Kuziel WA, Delbeck T, Mack M, et al. (2003) Monocytes are potent facilitators of alveolar neutrophil emigration during lung inflammation: role of the CCL2-CCR2 axis. J Immunol 170: 3273–3278.
- 64. Kipnis A, Basaraba R, Orme I, Cooper A (2003) Role of chemokine CCL2 in the protective response to early murine pulmonary tuberculosis. Immunology 109: 547–551.
- 65. Mordue DG, Sibley LD (2003) A novel population of Gr-1+-activated macrophages induced during acute toxoplasmosis. J Leukoc Biol 74: 1015–1025.
- 66. Robben PM, LaRegina M, Kuziel WA, Sibley LD (2005) Recruitment of Gr-1+ monocytes is essential for control of acute toxoplasmosis. J Exp Med 201: 1761–1769.
- 67. Landsman L, Varol C, Jung S (2007) Distinct differentiation potential of blood monocyte subsets in the lung. J Immunol 178: 2000–2007.
- 68. Lin Y, Ritchea S, Logar A, Slight S, Messmer M, et al. (2009) Interleukin-17 Is Required for T Helper 1 Cell Immunity and Host Resistance to the Intracellular Pathogen Francisella tularensis. Immunity 31: 799–810.
- 69. Daley JM, Thomay AA, Connolly MD, Reichner JS, Albina JE (2008) Use of Ly6G-specific monoclonal antibody to deplete neutrophils in mice. J Leukoc Biol 83: 64–70.
- 70. Wolf AJ, Desvignes L, Linas B, Banaiee N, Tamura T, et al. (2008) Initiation of the adaptive immune response to Mycobacterium tuberculosis depends on antigen production in the local lymph node, not the lungs. J Exp Med 205: 105–115.
- 71. Noss EH, Harding CV, Boom WH (2000) Mycobacterium tuberculosis inhibits MHC class II antigen processing in murine bone marrow macrophages. Cell Immunol 201: 63–74.
- 72. Fulton SA, Reba SM, Pai RK, Pennini M, Torres M, et al. (2004) Inhibition of major histocompatibility complex II expression and antigen processing in murine alveolar macrophages by Mycobacterium bovis BCG and the 19-kilodalton mycobacterial lipoprotein. Infect Immun 72: 2101–2110.
- 73. Jung YJ, Ryan L, LaCourse R, North RJ (2005) Properties and protective value of the secondary versus primary T helper type 1 response to airborne Mycobacterium tuberculosis infection in mice. J Exp Med 201: 1915–1924.
- 74. Khader SA, Bell GK, Pearl JE, Fountain JJ, Rangel-Moreno J, et al. (2007) IL-23 and IL-17 in the establishment of protective pulmonary CD4+ T cell responses after vaccination and during Mycobacterium tuberculosis challenge. Nat Immunol 8: 369–377.
- 75. Sadek MI, Sada E, Toossi Z, Schwander SK, Rich EA (1998) Chemokines induced by infection of mononuclear phagocytes with mycobacteria and present in lung alveoli during active pulmonary tuberculosis. Am J Respir Cell Mol Biol 19: 513–521.
- 76. Jones GS, Amirault HJ, Andersen BR (1990) Killing of Mycobacterium tuberculosis by neutrophils: a nonoxidative process. J Infect Dis 162: 700–704.
- 77. May ME, Spagnuolo PJ (1987) Evidence for activation of a respiratory burst in the interaction of human neutrophils with Mycobacterium tuberculosis. Infect Immun 55: 2304–2307.
- 78. Denis M (1991) Human neutrophils, activated with cytokines or not, do not kill virulent Mycobacterium tuberculosis. J Infect Dis 163: 919–920.
- 79. Seiler P, Aichele P, Bandermann S, Hauser AE, Lu B, et al. (2003) Early granuloma formation after aerosol Mycobacterium tuberculosis infection is regulated by neutrophils via CXCR3-signaling chemokines. Eur J Immunol 33: 2676–2686.