MAPKAP kinase 2 regulates IL-10 expression and prevents formation of intrahepatic myeloid cell aggregates during cytomegalovirus infections.

BACKGROUND & AIMS: The kinase p38(MAPK) and its downstream target MAPKAP kinase (MK) 2 are critical regulators of inflammatory responses towards pathogens. To date, the relevance of MK2 for regulating IL-10 expression and other cytokine responses towards cytomegalovirus (CMV) infection and the impact of this pathway on viral replication in vitro and in vivo is unknown and the subject of this study. METHODS: The effect of MK2, interferon-α receptor (IFNAR)1, tristetraprolin (TTP) and IL-10 on mouse (M)CMV virus titres, cytokine expression, signal transduction, transcript stability, liver enzymes release, immune cell recruitment and aggregation in response to MCMV infection were studied ex vivo in hepatocytes and macrophages, as well as in vivo. RESULTS: MK2 is critical for MCMV-induced production of IL-10, IFN-α2 and 4, IFN-ß, IL-6, and TNF-α but not for IFN-γ. The MCMV-induced IL-10 production requires activation of IFNAR1 and is further regulated by MK2 and TTP-dependent stabilization of IL-10 transcripts. MK2(-/-) mice are able to control acute MCMV replication, despite deregulated cytokine production. This may be related to the observation that MCMV-infected MK2(-/-) mice show enhanced formation of focal intrahepatic lymphocyte infiltrates resembling intrahepatic myeloid cell aggregates of T cell expansion (iMATEs), which were also observed in MCMV-infected IL-10(-/-) mice but are almost absent in MCMV-infected wild-type controls. CONCLUSIONS: The data suggest that MK2 is critical for regulating cytokine responses towards acute MCMV infection, including that of IL-10 via IFNARI-mediated circuits. MCMV stimulates expression of MK2-dependent cytokines, in particular IL-10 and thereby prevents enhanced formation of intrahepatic iMATE-like cellular aggregates.