Protective response in guinea pigs exposed to Mycobacterium aviumintracellulare/M. scrofulaceum, BCG & south Indian isolates of M. tuberculosis.

The protective immunity resulting from exposure to nontuberculous mycobacteria (NTM), BCG and virulent mycobacteria in different sequences was studied in the guinea pig model employing strains prevalent in the south Indian BCG trial area and time kinetics to observe the immuno-modulation. The findings suggest that during the early course of challenge infection in guinea pigs there was no interference with the immunity due to BCG, by prior exposure to NTM. In the animals sensitised with M. avium intracellulare before immunisation, the challenge infection was localised and confined to the site of inoculation, and only a few organisms reached the spleen. However, at the later stages of the infection, as seen by the spleen viable counts at 12 wk, it appeared that the barrier at the localised site of infection may not be intact in the animals with prior exposure to NTM, and a few organisms disseminate to the spleen.