Interleukin-21 maintains the expression of CD16 on monocytes via the production of IL-10 by human naïve CD4+ T cells.

Interleukin 21 exerts a variety of regulatory effects on both innate and adaptive immune cells. Although the suppressive effect of IL-21 via the induction of IL-10 in mouse model has been defined, the inhibitory effect of IL-21 in humans is not well understood. In the present study, we showed that IL-21 induced IL-10 production by human naive CD4(+) T cells. Most of the IL-10-producing CD4(+) T cells did not co-express IFN-γ. IL-21 increased the expression of IL-21R on activated naïve CD4(+) T cells. Further analysis indicated that IL-21 induced phosphorylation of STAT1, STAT3 and STAT5 in activated naïve CD4(+) T cells. In addition, IL-21 maintained the expression of CD16 on monocytes via the production of IL-10 by human naïve CD4(+) T cells. Taken together, our data indicated that IL-21 had a modulating effect on monocytes at least in part by inducing IL-10 production.