title: Antibody-mediated shift in the profile of glycoprotein A phenotypes observed in a mouse model of Pneumocystis carinii pneumonia.
abstract: It is well established that Pneumocystis carinii has the molecular capability for variation of a major surface antigen, glycoprotein A (gpA). However, the extent of expression of gpA variation among P. carinii organisms infecting a single host and whether this variation has any impact on host-parasite immunological interactions is unknown. Using a mouse model of P. carinii pneumonia, we were able to demonstrate the expression of more than one gpA phenotype in a closed population of infected mice. Administration of monoclonal antibody (MAb) 2B5, which is specific for one of the gpA phenotypes, resulted in a marked diminution in the frequency of this particular gpA phenotype in the population of organisms. This effect was due to a loss of trophozoites bearing the specific epitope recognized by MAb 2B5; cysts bearing the same epitope appeared unaffected. Interestingly, P. carinii was unable to introduce a new phenotype into the population to compensate for the loss of trophozoites bearing the epitope recognized by MAb 2B5. Discontinuing administration of MAb 2B5 allowed the MAb 2B5-binding phenotype to reemerge. This finding suggests that the phenotype recognized by MAb 2B5 was continually produced even when MAb 2B5 was present. Thus, although P. carinii exhibited a form of antigenic variation, it did not appear able to rapidly introduce new phenotypes into the population in response to destruction by antibodies.
authors.affiliation: Department of Pediatrics, University of Rochester School of Medicine, New York 14642, USA.
authors.forename: F
authors.initials: F
authors.lastname: Gigliotti
authors.forename: B A
authors.initials: BA
authors.lastname: Garvy
authors.forename: A G
authors.initials: AG
authors.lastname: Harmsen
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology*; D015153:Blotting, Western; D000939:Epitopes; D005434:Flow Cytometry; D005656:Fungal Proteins / Q000032:analysis / Q000276:immunology*; D008297:Male; D051379:Mice; D016513:Mice, SCID; D010641:Phenotype; D011020:Pneumonia, Pneumocystis / Q000276:immunology*
chemical_list: D000911:Antibodies, Monoclonal; D000939:Epitopes; D005656:Fungal Proteins