Re-evaluation of IL-10 signaling reveals novel insights on the contribution of the intracellular domain of the IL-10R2 chain

Interleukin-10 (IL-10) is an anti-inflammatory cytokine that plays a key role in maintainingimmune homeostasis. IL-10-mediated responses are triggered upon binding to a heterodimericreceptor complex consisting of IL-10 receptor (IL-10R)1 and IL-10R2. Engagementof the IL-10R complex activates the intracellular kinases Jak1 and Tyk2, but the exact rolesof IL-10R2 and IL-10R2-associated signaling via Tyk2 remain unclear. To elucidate the contributionof IL-10R2 and its signaling to IL-10 activity, we re-evaluated IL-10-mediatedresponses on bone marrow-derived dendritic cells, macrophages and mast cells. By usingbone marrow from IL-10R-/- mice it was revealed that IL-10-mediated responses depend onboth IL-10R1 and IL-10R2 in all three cell types. On the contrary, bone marrow-derived cellsfrom Tyk2-/- mice showed similar responses to IL-10 as wild-type cells, indicating that signalingvia this IL-10R2-associated kinase only plays a limited role. Tyk2 was shown to controlthe amplitude of STAT3 activation and the up-regulation of downstream SOCS3 expression.SOCS3 up-regulation was found to be cell-type dependent and correlated with the lack ofearly suppression of LPS-induced TNF-α in dendritic cells. Further investigation of the IL-10R complex revealed that both the extracellular and intracellular domains of IL-10R2 influencethe conformation of IL-10R1 and that both domains were required for transducing IL-10 signals. This observation highlights a novel role for the intracellular domain of IL-10R2 inthe molecular mechanisms of IL-10R activation.