Host species-specific antigenic variation of a mannosylated surface glycoprotein of Pneumocystis carinii.

All Pneumocystis carinii, irrespective of their host of origin, express an abundant mannosylated surface glycoprotein. While this molecule is commonly referred to as gp120, some variation in the size of this molecule has been noted. Monoclonal antibodies produced to this molecule from ferret, mouse, rat, and human P. carinii made it possible to distinguish the glycoprotein from P. carinii of each host by immunoblot and indirect immunofluorescence assays. The glycoprotein varied in size (approximately 95-140 kDa) depending on the host and method of preparation. One shared epitope involving the mannose part of the glycoprotein was identified, suggesting that despite size and antigenic differences these are homologous molecules. These results indicate the existence of host species-specific serotypes of P. carinii. Referring to this molecule by its molecular mass may be confusing; therefore, it is suggested that this glycoprotein be called surface glycoprotein A, as this was the initial molecule of P. carinii to be isolated and partially characterized.