Immunological and Genetical Heterogeneity of Pneumocystis carinii

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Opportunistic infections caused by Pneumocystis organisms have been reported in a variety of mammals including pigs, horses, ferrets, rats, mice, and humans. Pneumocystis organisms from those animals has long been considered to belong to the only species, Pneumocystis carinii, leading the speculation that P.carinii pneumonia is zoonosis. P.carinii is clearly transmissible between animals of the same species by the airborne route under controlled experimental conditions. However, the ability of P.carinii from one host species to infect members of another species is unclear. Attempts of morphological distinguishment of the organisms were difficult because of their resemblance. In the present study, we performed serodeme, schizodeme and zymodene analyzes to study both phenotype and genotype variation among Pneumocystis organisms from different host species. For serodeme analysis, we employed an indirect fluorescence antibody technique and a Western blot technique with the use of monoclonal and polyclonal antibodies raised against Pneumocystis organisms from mice, rats, and humans. Serodeme and zymodeme analyzes clearly demonstrated the differences of their phenotypes. Schizodeme analysis using polymerase chain reaction with specific primers for rat and mouse-derived organisms followed by treatment of the products by restriction enzymes confirmed genotype differences among organisms. The availability of techniques and reagents with which we could unequivocally distinguish between rats, mice, and human Pneumocystis organisms is prompting us to reexamine the issue of transmission of P.carinii from one host species to another.