T-cell contributions to alveolar bone loss in response to oral infection with Porphyromonas gingivalis

Abstract

We have previously shown that mice lacking CD4⁺, but not CD8⁺, T cells lose less alveolar bone loss in response to oral infection with Porphyromonas gingivalis than do immunocompetent mice of the same genetic background, indicating that CD4⁺ T cells contribute to bone resorption. The CD4⁺ and CD8⁺ T-cell knockouts were produced by targeted deletions of, respectively, major histocompatibility complex II (MHCII) or β₂-microglobulin (producing non-expression of MHCI). Because MHC deletions can have other effects in addition to those on T-cell selection, we wanted to confirm that the lessened bone loss was truly an effect of the lack of T cells. Consequently, we repeated our experiments with C57B1/6J-Tcra mice that have a targeted deletion of the alpha chain of the T-cell receptor (Tcra). Six weeks after oral infection with P. gingivalis ATCC 53977 the total bone loss at buccal maxillary sites was 0.28 mm in infected immunocompetent mice (P = 0.002 compared with sham-infected mice), whereas in Tcra knockouts the bone loss was only 0.08 mm (P = 0.04 compared with shams). The T-cell-deficient mice thus lost 70% less bone after infection than did genetically matched immunocompetent mice (P = 0.003). These experiments confirm that T cells, and their responses to oral infection with P. gingivalis, help to push bone remodeling in the direction of net loss of bone.