The in vitro response of human lymphocytes to Pneumocystis carinii antigen.

Pneumocystis carinii pneumonitis (PCP) is a major complication in the immunocompromised host. Recent evidence suggests that most normal individuals have detectable antibody against this organism. The role of the various components of the immune system in protecting the host from acute PCP is unclear. We have examined the in vitro proliferative response of lymphocytes from normal adults to P. carinii antigen. Fourteen of 16 subjects had a positive response with stimulation indices greater than 3. This response was due primarily to thymus-derived (T cell) lymphocytes and was dependent upon the presence of adherent cells. The response was most likely not due to a mitogenic component in our antigen preparation, since lymphocytes from only 2 of 16 cord blood specimens had stimulation indices greater than 3.