The MAPK-Activated Kinase MK2 Attenuates Dendritic Cell-Mediated Th1 Differentiation and Autoimmune Encephalomyelitis

Dendritic cell (DC)-mediated inflammation induced via TLRs is promoted by MAPK-activated protein kinase (MK)-2, a substrate of p38 MAPK. In this study we show an opposing role of MK2, by which it consolidates immune regulatory functions in DCs through modulation of p38, ERK1/2-MAPK, and STAT3 signaling. During primary TLR/p38 signaling, MK2 mediates the inhibition of p38 activation and positively cross-regulates ERK1/2 activity, leading to a reduction of IL-12 and IL-1a/b secretion. Consequently, MK2 impairs secondary autocrine IL-1a signaling in DCs, which further decreases the IL-1a/p38 but increases the anti-inflammatory IL-10/STAT3 signaling route. Therefore, the blockade of MK2 activity enables human and murine DCs to strengthen proinflammatory effector mechanisms by promoting IL-1a-mediated Th1 effector functions in vitro. Furthermore, MK2-deficient DCs trigger Th1 differentiation and Ag-specific cytotoxicity in vivo. Finally, wild-type mice immunized with LPS in the presence of an MK2 inhibitor strongly accumulate Th1 cells in their lymph nodes. These observations correlate with a severe clinical course in DC-specific MK2 knockout mice compared with wild-type littermates upon induction of experimental autoimmune encephalitis. Our data suggest that MK2 exerts a profound anti-inflammatory effect that prevents DCs from prolonging excessive Th1 effector T cell functions and autoimmunity.