Blastogenic responses to Pneumocystis carinii among patients with human immunodeficiency (HIV) infection.

Proliferative responses by human peripheral blood mononuclear cells and rat spleen cells were measured to Pneumocystis carinii in a blastogenic assay using organisms obtained from rat lungs and propagated in tissue culture as the antigen. Responses occurred only in subjects with known prior exposure to P. carinii and the magnitude of the response varied with the number of organisms present in the antigen preparation and days in culture. Healthy human adults showed higher proliferative responses to P. carinii than did patients with Class II (asymptomatic) or Class III (lymphadenopathy) human immunodeficiency virus (HIV) infection. No responses to the preparation were found among Class IV HIV patients with the acquired immunodeficiency syndrome, including those with prior episodes of P. carinii pneumonia or those receiving azidothymidine. Overall, the blastogenic responses obtained with P. carinii were similar to those obtained with tetanus toxoid and phytohemagglutinin, and correlated well with the number of circulating CD4 cells. The data suggest that the blastogenic assay using tissue culture-derived rat P. carinii is specific for the organism and should be helpful in studying the cellular immune responses in pneumocystosis among different human patient populations.