CD4+CD25+ regulatory T (Tr) cells are critical in regulating the immune response and thereby play an important role in the defense against infection and control of autoimmune diseases. Our previous studies demonstrated the involvement of autoimmune responses in periodontitis. The aim of this study was to identify CD4+CD25+ Tr cells in periodontitis tissues and compare them with those in gingivitis tissues. Immunohistological analysis of CD4, CD25, and CTLA-4 and the gene expression analysis of FOXP3, TGF-beta1, and IL-10 on gingival biopsies revealed the presence of CD4+CD25+ Tr cells in all tissues. In periodontitis, the percentage of CD4+CD25+ Tr cells increased with increasing proportions of B-cells relative to T-cells. FOXP3, a characteristic marker for CD4+CD25+ Tr cells, TGF-beta1 and IL-10 were expressed more highly in periodontitis compared with gingivitis. These findings suggest that CD4+CD25+ Tr cells and possibly other regulatory T-cell populations do exist and may play regulatory roles in periodontal diseases.

Although periodontal infection does affect the concentration of hs-CRP and IL-6 in serum, a subgroup of patients exist who are highly susceptible to an increased risk of CHD associated with periodontitis, suggesting that there may be subjects who have an elevated risk of CHD independent of susceptibility to periodontal tissue destruction per se.

Increasing evidence suggests that distinct inflammatory cytokines convert forkhead box protein P3 (FOXP3(+)) regulatory T-cells (Tregs) into IL-17-producing cells (Th17 cells) in vitro. However, this functional plasticity has not been examined in the pathogenesis of periodontal disease. In this study, we analyzed the IL-17A(+)FOXP3(+) cells present in periodontitis lesions to determine the association between Treg conversion and the pathogenesis of periodontitis. The immunohistochemical analysis of gingival tissues demonstrated that the numbers of Th17 cells (IL-17A(+)FOXP3(-)) and Tregs (IL-17A(-)FOXP3(+)) were greater in periodontitis lesions than in gingivitis lesions. We further identified a small number of IL-17A(+)FOXP3(+) cells in periodontitis lesions but not in gingivitis lesions. The flow cytometry analysis of CD4(+) T-cell lines established from gingival tissues and the peripheral blood of periodontitis patients showed that the proportion of Tregs was reduced and the proportion of IL-17A(+)FOXP3(+) cells among all FOXP3(+) cells was elevated in gingival tissue T-cell lines relative to the proportions in peripheral blood T-cell lines. Our findings indicate that Treg-Th17 conversion may occur in periodontitis lesions. Further studies addressing the role of Treg conversion during inflammatory responses against periodontopathic bacteria are needed.

Heat shock protein 60s (hsp60) are remarkably immunogenic, and both T-cell and antibody responses to hsp60 have been reported in various inflammatory conditions. To clarify the role of hsp60 in T-cell responses in periodontitis, we examined the proliferative response of peripheral blood mononuclear cells (PBMC), as well as the cytokine profile and T-cell clonality, for periodontitis patients and controls following stimulation with recombinant human hsp60 and Porphyromonas gingivalis GroEL. To confirm the infiltration of hsp60-reactive T-cell clones into periodontitis lesions, nucleotide sequences within complementarity-determining region 3 of the T-cell receptor (TCR) ␤-chain were compared between hsp60-reactive peripheral blood T cells and periodontitis lesion-infiltrating T cells. Periodontitis patients demonstrated significantly higher proliferative responses of PBMC to human hsp60, but not to P. gingivalis GroEL, than control subjects. The response was inhibited by anti-major histocompatibility complex class II antibodies. Analysis of the nucleotide sequences of the TCR demonstrated that human hsp60-reactive T-cell clones and periodontitis lesion-infiltrating T cells have the same receptors, suggesting that hsp60-reactive T cells accumulate in periodontitis lesions. Analysis of the cytokine profile demonstrated that hsp60-reactive PBMC produced significant levels of gamma interferon (IFN-␥) in periodontitis patients, whereas P. gingivalis GroEL did not induce any skewing toward a type1 or type2 cytokine profile. In control subjects no significant expression of IFN-␥ or interleukin 4 was induced. These results suggest that periodontitis patients have human hsp60-reactive T cells with a type 1 cytokine profile in their peripheral blood T-cell pools.