The effect of combined chemotherapy on suppressor T-cell activity in Mycobacterium simiae-infected mice

Specific pathogen-free B6D2 mice were infected with 10(6) or 10(8) viable Mycobacterium bovis (BCG Pasteur) or Mycobacterium simiae and the in vivo growth curves were correlated with the levels of delayed hypersensitivity developed against a cytoplasmic protein antigen (CPA) injected into a hind footpad at increasing time intervals after infection. Half of the heavily infected, anergic mice were placed on a regimen of 10 mg of rifampin, 5 mg of amikacin and 2 mg of clofazimine per 100 ml of drinking water 2 or 8 weeks into the infection. The number of viable mycobacteria recovered from the lungs and spleens of the treated mice (compared with the corresponding drug-free controls) were reduced by up to 10,000-fold over a 3-month treatment period. Spleen cells were harvested at increasing time intervals from the drug-treated and control mice and T-cell enriched suspensions were tested for blastogenic responsiveness to phytohaemagglutinin (PHA) and to the specific CPA mitogen. The early (day 14) peak in tritiated thymidine ([3H]-TdR) uptake was followed by a sharp drop to near background levels. Cell-mixing experiments demonstrated the presence of a suppressor T-cell population in the heavily infected spleens of the M. simiae-infected mice. The suppressor-cell effect was substantially reduced following combined drug therapy although the specific CPA-mediated response was less affected than the non-specific PHA-mediated response.