Dendritic cells from Crohn's disease patients show aberrant STAT1 and STAT3 signaling.

Abstract

Abnormalities of dendritic cells (DCs) and STAT proteins have been reported in Crohn's disease (CD). Studies on JAK/STAT signaling in DCs are, however, lacking in CD. We applied a flowcytometric single-cell-based phosphoepitope assay to evaluate STAT1 and STAT3 pathways in DC subsets from CD patients. In addition, circulating DC counts were determined, together with the activation-related immunophenotype. We found that IL-6- and IFN-α-induced STAT3 phosphorylation and IFN-α-induced STAT1 phosphorylation were impaired in plasmacytoid DCs (pDCs) from CD patients (P = 0.005, P = 0.013, and P = 0.006, respectively). In myeloid DCs (mDCs), IFN-α-induced STAT1 and STAT3 phosphorylation were attenuated (P<0.001 and P = 0.048, respectively), but IL-10-induced STAT3 phosphorylation was enhanced (P = 0.026). IFN-γ-induced STAT1 signaling was intact in both DC subtypes. Elevated plasma IL-6 levels were detected in CD (P = 0.004), which strongly correlated with disease activity (ρ = 0.690, P<0.001) but not with IL-6-induced STAT3 phosphorylation. The numbers of pDCs and BDCA3+ mDCs were decreased, and CD40 expression on CD1c+ mDCs was increased in CD. When elucidating the effect of IL-6 signaling on pDC function, we observed that IL-6 treatment of healthy donor pDCs affected the maturation of and modified the T-cell priming by pDCs, favoring Th2 over Th1 type of response and the expression of IL-10 in T cells. Our results implicate DC signaling in human CD. Reduced IL-6 responsiveness in pDCs, together with the attenuated IFN-α-induced signaling in both DC subtypes, may contribute to the immunological dysregulation in CD patients.