The suppressive effect of M. leprae on the in vitro proliferative responses of lymphocytes from patients with leprosy.

Peripheral blood lymphocytes from sixty leprosy patients and eight healthy contacts known to be responsive to M. leprae, were stimulated in vitro with concanavalin A (Con A) or PPD alone or in combination with autoclaved, whole M. leprae. Time kinetics and the percentage of inhibition induced by M. leprae differed in the two disease groups and contacts. Antigen-generated suppression of Con A-stimulated lymphocyte transformation was observed on day 4 in seventeen of twenty-one (80%) tuberculoid patients and six of seventeen (35.3%) untreated lepromatous patients. Healthy contacts and 53% lepromatous individuals showed enhanced Con A responses in the presence of antigen. On prolongation of antigen presence to 6 days, a marginal effect was noted in the tuberculoid group. In contrast, all healthy individuals and some lepromatous patients showed increased inhibition of Con A responses. M. leprae antigens showed uniform inhibition of PPD-induced 3H-thymidine incorporation in leprosy patients and healthy contacts.