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Infect. Immun., Jun 1996, 1892-1899, Vol 64, No. 6
F Gigliotti, BA Garvy and AG Harmsen
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.
Copyright © 1996, American Society for Microbiology
Antibody-mediated shift in the profile of glycoprotein A phenotypes observed in a mouse model of Pneumocystis carinii pneumonia
Department of Pediatrics, University of Rochester School of Medicine, New York 14642, USA.
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