Immunity to leprosy. III. The in vitro induction of B lymphocyte proliferation by mycobacteria.

The development of murine proliferative response assays has been initiated to begin to evaluate T-lymphocyte responses to the antigens of Mycobacterium leprae. In this study, M. leprae and 13 related strains of mycobacteria have been tested for stimulatory effects in proliferation assays using murine spleen, thymus or lymph node cultures. A number of mycobacteria were found to directly stimulate the proliferation of spleen and lymph node cells of all mouse strains tested including C3H/HeJ mice. Thymocyte cultures showed no response. The mitogenic effects of mycobacteria in spleen cultures were not dependent upon the presence of T cells or adherent cells, and resulted in the production of antibody-forming cells. Thus, these bacteria acted as polyclonal B-cell mitogens and could be readily distinguished from the lipopolysaccharide of Gram-negative bacteria by their mitogenic activity on C3H/HeJ spleen cells. The species of mycobacteria which exhibit direct mitogenic effects in spleen and lymph node cultures are a particular problem when specific immune responses to the antigens of these bacteria are compared. Such comparisons are necessary if in vitro assays are to be used to determine the nature of crossreactive antigens between M. leprae and other mycobacteria.