Effect of Mycobacterium leprae on lymphocyte proliferation: suppression of mitogen and antigen responses of human peripheral blood mononuclear cells.

Evidence is presented that Mycobacterium leprae suppresses the in vitro proliferative response of human peripheral blood mononuclear cells (PBM) to antigen and mitogen. Lymphoproliferation induced by PPD or alloantigen stimulation was inhibited by concentrations of M. leprae which were not cytotoxic for lymphoblasts. In contrast, the inhibition of mitogen-stimulated PBM was seen only at higher concentrations of M. leprae which proved to be cytotoxic for lymphoblasts. The inhibitory effect was found not to be dependent on a particular cell population present in leprosy patients, as PBM from normal were inhibited similarly. These findings may explain some of the immunological aberrations observed in lepromatous leprosy patients who harbour large numbers of M. leprae bacilli in their tissues.