Animal studies define CD4+CD25+ T cells as a subset that protect against autoimmune inflammation. The role for these cells in human autoimmune inflammatory conditions of the oral cavity is not known. Objectives: Here, we wanted to investigate whether CD4+CD25+ T cells from patients with recurrent tonsillitis could suppress proliferation of other tonsil cells, in vitro, as this immunological tissue also may serve as a model for chronic inflammation. Methods: Subsets of T cells were purified on columns and 3H-thymidine incorporation was used to measure proliferation in 3-day cell cultures. Results: Tonsil CD4+CD25+ cells markedly suppressed the proliferation of CD4+CD25- T cells in concanavalin A-stimulated co-cultures compared with cultures containing CD4+CD25- T cells only. The suppression exerted by the CD4+CD25+ cells was abrogated if these cells were irradiated before co-culture or if IL-2 was added to the culture medium. CD4+CD25+ T cells proliferated poorly in response to mitogen, when cultured alone. Substitution with CD4+CD25+ T cells isolated from peripheral blood, treated alike, did not down-regulate the proliferation of CD4+CD25- responder cells from tonsils, in 3-day co-cultures. The augmented suppressive ability of tonsil CD4+CD25+ T cells compared with cells of this phenotype from blood on CD4+CD25- responder cells from tonsils, suggests that there may be a functional difference between CD25+ cells from the two locations. Conclusions: CD4+CD25+ T cells from inflamed tonsils distinctly suppressed T cell responses to mitogen in vitro, pointing to a regulatory role for CD4+CD25+ cells retrieved from inflammatory reactions in humans.

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