Type I interferons maintain Foxp3 expression and T-regulatory cell functions under inflammatory conditions in mice.

BACKGROUND & AIMS Foxp3(+) T-regulatory cells (Tregs) maintain intestinal homeostasis under conditions of continuous challenge with inflammatory microbes. However, plasticity of the Treg population under certain conditions has been reported; Foxp3(+) Tregs can be converted to Foxp3(-) CD4(+) T cells. METHODS We used mice with a T cell-induced colitis model to study the regulatory role of type I interferons (IFNs) in adaptive immunity. We transferred CD4(+)CD45RB(hi) (RB(hi)) T cells, with or without CD4(+)CD45RB(lo) CD25(+) T cells, from wild-type or IFN-αβR(-/-) mice into Rag1(-/-) recipients. We analyzed induction of colitis by flow cytometry, confocal microscopy, and enzyme-linked immunosorbent assay and reverse-transcription polymerase chain reaction analyses. IFN-αβR(-/-)Rag(-/-) mice were given injections of recombinant IFN-α following transfer of IFN-αβR(-/-) RB(hi) T cells and CD4(+)Foxp3(+) cells from Foxp3-eGFP mice. RESULTS Signaling by type I IFNs was required for maintenance of Foxp3 expression and the suppressive activity of Tregs in mice. Transfer of CD4(+)CD45RB(lo)CD25(+) Tregs from IFN-αβR(-/-) mice did not prevent T-cell induction of colitis in mice. Foxp3 expression by Tregs transferred from IFN-αβR(-/-) mice was significantly lower than that of Tregs from wild-type mice. Administration of recombinant IFN-α reduced T cell-mediated colitis by increasing the number of Foxp3(+) Tregs and their suppressive functions. CONCLUSIONS Type I IFNs regulate intestinal homeostasis by maintaining Foxp3 expression on Tregs in colons of mice under inflammatory conditions.