CD4+CD25+ T lymphocytes in human tonsils suppress the proliferation of CD4+CD25- tonsil cells

Animal studies define CD4+CD25+ T cells as a subset that protect against autoimmune inflammation. We wanted to investigate whether CD4+CD25+ T cells from patients with recurrent tonsillitis could suppress the proliferation of other tonsil cells, in vitro, as this immunological tissue also may serve as a model for chronic inflammation. Tonsil CD4+CD25+ cells markedly suppressed the proliferation of CD4+CD25- T cells in Concanavalin A-stimulated cocultures 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 coculture or if interleukin (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, enriched by similar methods, did not downregulate the proliferation of CD4+CD25- responder cells from tonsils. 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. In conclusion, 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.