Proliferative and cytokine responses to a major surface glycoprotein of Pneumocystis carinii.

Naturally derived T-cell responses by rats to a 120-kDa major surface glycoprotein (MSG) of rat-derived Pneumocystis carinii were analyzed in vitro. Specific cytokines elicited by the T-cell response to the MSG were also identified. MSG was purified from rat-derived P. carinii by three different techniques: lectin affinity chromatography, sodium dodecyl sulfate-polyacrylamide gel electrophoresis followed by electroelution, and size-exclusion high-performance liquid chromatography. The cell-mediated immunity of spleen cells isolated from Lewis rats with and without natural exposure to P. carinii to the purified MSG was studied. Exposure to P. carinii was monitored by the presence or absence of serum antibodies to P. carinii antigens by Western blotting (immunoblotting). A T-cell proliferative response to the MSG was identified only with spleen cells isolated from rats exposed to P. carinii and peaked at 4 days. Flow cytometric analysis revealed that the percentage of CD4 cells was significantly increased during the proliferative response to MSG. MSG also elicited secretion of tumor necrosis factor alpha, interleukin-1, and interleukin-2, with peak activity of these cytokines occurring after 12, 24, and 48 h, respectively, of culture. These findings suggest that MSG is important in host T-cell recognition of and immune response to P. carinii by recruitment of inflammatory cells and cytokine production.