IMMUNE-RESPONSE AND MODULATION OF IMMUNE-RESPONSE INDUCED IN THE GUINEA-PIGS BY MYCOBACTERIUM-AVIUM COMPLEX (MAC) AND M-FORTUITUM COMPLEX ISOLATES FROM DIFFERENT SOURCES IN THE SOUTH INDIAN BCG TRIAL AREA

A total of 139 guineapigs were used to study the immune response and i ts modulation induced by Myobacterium avium complex: (MAC) and M. fort uitum complex strains obtained from different sources in the south Ind ian BCG trial area. The guineapigs were divided into groups and some w ere directly sensitised/immunised with different MAC strains, M. fortu itum complex strain or BCG and others were sensitised with MAC or M. f ortuitum complex and then immunised with BCG. The resulting delayed ty pe hypersensitivity (DTH) response in the different groups of guineapi ps was studied by skin tests using PPD-RT23 and PPD-B, and protective response was studied by challenging the guineapigs with a south Indian low virulent strain of M. tuberculosis and enumerating the bacilli in spleen at different points of time. The 3 strains of MAC induced simi lar low levels of DTA to PPD-RT23 but much higher and varying levels o f DTH to PPD-B. MAC strains from soil and sputum induced different lev els of immune modulation during subsequent immunisation with BCG on th e DTH response to PPD-KT23 and PPD-B, At 2 wk after challenge, 23.8, 8 1 and 90.5 per cent protection was induced by the standard strain, soi l isolate and sputum isolate of MAC, respectively, while 33.3 per rent protection was induced by the M. fortuitum complex strain compared to the protection induced by BCC alone. Prior exposure to MAC or M. fort uitum complex did not have any modulatory effect on the protective imm unity due to BCG at this time point. However, at 6 wk after challenge, while the guineapigs immunised with BCG were protected, modulation of the protective response resulting from BCG was observed in the guinea pigs sensitised with MAC and M. fortuitum from soil.