Exposure of myeloid dendritic cells to exogenous or endogenous IL-10 during maturation determines their longevity.

Dendritic cells (DC) are essential for the initiation of primary adaptive immune responses, and their functionality is strongly down-modulated by IL-10. Both innate and adaptive immune signals trigger the up-regulation of antiapoptotic Bcl-2 family members to facilitate the survival of DCs after maturation. However, whether IL-10 alters the expression of apoptotic-related genes in maturing DCs has not been determined. In this study, we demonstrate that spontaneous apoptosis rapidly occurred in myeloid DCs exposed to exogenous IL-10 upon maturation. Microarray analysis indicates that IL-10 suppressed the induction of three antiapoptotic genes, bcl-2, bcl-x, and bfl-1, which was coincident with the increased sensitivity of mature DCs to spontaneous apoptosis. IL-10 markedly inhibited the accumulation of steady state Bcl-2 message and protein in myeloid DCs activated through TLRs or TNFR family members, whereas exogenous IL-10 affected Bcl-x(L) expression in a moderate manner. In contrast, bcl-2 expression of plasmacytoid DCs was less sensitive to the effects of IL-10. We further show that autocrine IL-10 significantly limited the longevity of myeloid DCs and altered the expression kinetics of Bcl-2 but not Bcl-x(L) in maturing DCs. We conclude that the degree of IL-10 exposure and/or the level of endogenous IL-10 production upon myeloid DC maturation play a critical role in determining DC longevity. This regulatory mechanism of IL-10 is associated with the dynamic control of antiapoptotic Bcl-2 proteins.