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We examined splenic T cell proliferative and cytokine as well as serum antibody responses to recombinant and native<jats:italic>Pneumocystis<\/jats:italic>antigens in immunized or<jats:italic>Pneumocystis<\/jats:italic>-infected mice. In addition, immune responses were examined in 5 healthy humans.<\/jats:p><\/jats:sec><jats:sec><jats:title>Results<\/jats:title><jats:p>Proliferative responses to each of two recombinant Msg variant proteins were seen in mice immunized with either recombinant protein, but no proliferation to these antigens was seen in mice immunized with crude<jats:italic>Pneumocystis<\/jats:italic>antigens or in mice that had cleared infection, although the latter animals demonstrated proliferative responses to crude<jats:italic>Pneumocystis<\/jats:italic>antigens and native Msg. IL-17 and MCP-3 were produced in previously infected animals in response to the same antigens, but not to recombinant antigens. Antibody responses to the recombinant<jats:italic>P. murina<\/jats:italic>Msg variant proteins were seen in all groups of animals, demonstrating that all groups were exposed to and mounted immune responses to Msg. No human PBMC samples proliferated following stimulation with<jats:italic>P. jirovecii<\/jats:italic>Msg, while antibody responses were detected in sera from 4 of 5 samples.<\/jats:p><\/jats:sec><jats:sec><jats:title>Conclusions<\/jats:title><jats:p>Cross-reactive antibody responses to Msg variants are common, while cross-reactive T cell responses are uncommon; these results support the hypothesis that<jats:italic>Pneumocystis<\/jats:italic>utilizes switching of Msg variant expression to avoid host T cell responses.<\/jats:p><\/jats:sec>","DOI":"10.1186\/1471-2172-13-39","type":"journal-article","created":{"date-parts":[[2012,7,13]],"date-time":"2012-07-13T17:33:07Z","timestamp":1342200787000},"update-policy":"https:\/\/doi.org\/10.1007\/springer_crossmark_policy","source":"Crossref","is-referenced-by-count":26,"title":["Discordant antibody and cellular responses to Pneumocystis major surface glycoprotein variants in mice"],"prefix":"10.1186","volume":"13","author":[{"given":"Lisa R","family":"Bishop","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Daniel","family":"Helman","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Joseph A","family":"Kovacs","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"297","published-online":{"date-parts":[[2012,7,12]]},"reference":[{"key":"444_CR1","doi-asserted-by":"publisher","first-page":"937","DOI":"10.1084\/jem.172.3.937","volume":"172","author":"AG Harmsen","year":"1990","unstructured":"Harmsen AG, Stankiewicz M: Requirement for CD4+ cells in resistance to Pneumocystis carinii pneumonia in mice. 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