Pneumocystis carinii organisms obtained from rats, ferrets, and mice are antigenically different.

Pneumocystis carinii infections were developed in animals immunosuppressed by dexamethasone treatment either from activation of latent infection (ferret) or by transtracheal inoculation with P. carinii-infected lung tissue from the homologous species (rat or mouse). Convalescent-phase antisera were obtained by stopping dexamethasone treatment after 2 to 4 weeks and allowing animals 5 to 8 weeks for recovery. P. carinii harvests from infected lungs were purified by differential filtration, solubilized in buffer containing urea, sodium dodecyl sulfate (SDS), and 2-mercaptoethanol, subjected to SDS-polyacrylamide gel electrophoresis, and blotted to polyvinylidene difluoride sheets for Western immunoblot analysis. These lung preparations are hereafter referred to as P. carinii antigens. Convalescent-phase antisera from each animal species were reacted on Western blots of P. carinii antigens prepared from organisms isolated from rats, ferrets, or mice. Each combination of P. carinii antigens and antisera from the same species of animal reacted with three or more P. carinii antigen proteins. Convalescent-phase mouse antisera reacted with P. carinii antigens from mice but not rats or ferrets. Convalescent-phase rat antisera reacted with P. carinii antigens from rats and mice but not ferrets, and convalescent-phase ferret antisera showed reactions with ferret and mouse P. carinii antigens but not rat antigens. These findings indicate antigenic differences among P. carinii strains infecting these animals.