Pneumocystis carinii: immunoblotting and immunofluorescent analyses of serum antibodies during experimental rat infection and recovery.

Serum antibodies to Pneumocystis carinii were measured in rats by the indirect fluorescent antibody and immunoblotting techniques. Serum IgG and IgM antibodies developed with environmental exposure to P. carinii, were low or absent during immunosuppression to induce P. carinii pneumonia, and rose when immunosuppression was withdrawn. The IgG and IgM antibodies formed at the same time, but the titers of each antibody varied in individual rats. Serum IgG antibodies by immunoblotting recognized bands of 45, 50, and 116 kDa as the major reactive moieties of P. carinii. The bands were detected with sera from all rat groups in a temporal pattern which closely paralleled antibody formation by indirect immunofluorescence. The pattern of immunoblotting reactivity varied among individual rats, particularly with immunosuppression. Additional bands were detected with prolonged exposure to P. carinii. Thus, the rat makes both IgG and IgM antibodies to P. carinii, and specific P. carinii antigens identified in this immune response might be targeted for future serologic studies.