Survival curves of BCG vaccinated guinea pigs (triangles) and unvaccinated guinea pigs (open squares) after M. tuberculosis infection. The animals were sacrificed when they had lost 15% of the maximum weight or had clinical symptoms indicative of severe TB (Fig 1A). Mean skin test reaction (+/−SEM) for M. tuberculosis-infected unimmunized and BCG vaccinated guinea pigs (n = 7), measured as erythema after intradermal injection of 2 ug E6/C10 (Fig. 1B) or 10 T.U. PPD (Fig. 1C). Each animal received a maximum of 4 tests with more than 8 weeks interval and this schedule did not sensitize naïve animals. The experiment was repeated twice with the same overall result and data shown for a representative experiment.