IL-10-Secreting Regulatory T Cells Do Not Express Foxp3 but Have Comparable Regulatory Function to Naturally Occurring CD4+CD25+ Regulatory T Cells

Regulatory T cells (T(Reg)) control immune responses to self and nonself Ags. The relationship between Ag-driven IL-10-secreting T(Reg) (IL-10-T(Reg)) and naturally occurring CD4(+)CD25(+) T(Reg) is as yet unclear. We show that mouse IL-10-T(Reg) obtained using either in vitro or in vivo regimens of antigenic stimulation did not express the CD4(+)CD25(+) T(Reg)-associated transcription factor Foxp3. However, despite the absence of Foxp3 expression, homogeneous populations of IL-10-T(Reg) inhibited the in vitro proliferation of CD4(+)CD25(-) T cells with a similar efficiency to that of CD4(+)CD25(+) T(Reg). This inhibition of T cell proliferation by IL-10-T(Reg) was achieved through an IL-10-independent…