Immune response & modulation of immune response induced in the guineapigs
by Mycobacterium avium complex (MAC) & 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 its modulation induced by
Mycobacterium avium complex (MAC) and M. fortuitum complex strains obtained from different
sources in the south Indian BCG trial area. The guineapigs were divided into groups and some were
directly sensitised/immunised with different MAC strains, M. fortuitum complex strain or BCG and
others were sensitised with MAC or M. fortuitum complex and then immunised with BCG. The
resulting delayed type hypersensitivity (DTH) response in the different groups of guineapigs 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 similar low levels of DTH
to PPD-RT23 but much higher and varying levels of DTH to PPD-B. MAC strains from soil and
sputum induced different levels of immune modulation during subsequent immunisation with BCG
on the DTH response to PPD-RT23 and PPD-B. At 2 wk after challenge, 23.8, 81 and 90.5 per cent
protection was induced by the standard strain, soil isolate and sputum isolate of MAC, respectively,
while 33.3 per cent protection was induced by the M. fortuitum complex strain compared to the
protection induced by BCG alone. Prior exposure to MAC or M. fortuitum complex did not have
any modulatory effect on the protective immunity 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 guineapigs sensitised with MAC and
M. fortuitum from soil