Protein tyrosine phosphatase PTPN22 regulates IL-1β dependent Th17 responses by modulating dectin-1 signaling in mice

A single nucleotide polymorphism within the PTPN22 gene is a strong genetic risk factor predisposing to the development of multiple autoimmune diseases. PTPN22 regulates Syk and Src family kinases downstream of immuno-receptors. Fungal β-glucan receptor dectin-1 signals via Syk, and dectin-1 stimulation induces arthritis in mouse models. We investigated whether PTPN22 regulates dectin-1 dependent immune responses. Bone marrow derived dendritic cells (BMDCs) generated from C57BL/6 wild type (WT) and Ptpn22^−/− mutant mice, were pulsed with OVA_323-339 and the dectin-1 agonist curdlan and co-cultured in vitro with OT-II T-cells or adoptively transferred into OT-II mice, and T-cell responses were determined by immunoassay. Dectin-1 activated Ptpn22^−/− BMDCs enhanced T-cell secretion of IL-17 in vitro and in vivo in an IL-1β dependent manner. Immunoblotting revealed that compared to WT, dectin-1 activated Ptpn22^−/− BMDCs displayed enhanced Syk and Erk phosphorylation. Dectin-1 activation of BMDCs expressing Ptpn22^R619W (the mouse orthologue of human PTPN22^R620W) also resulted in increased IL-1β secretion and T-cell dependent IL-17 responses, indicating that in the context of dectin-1 Ptpn22^R619W operates as a loss-of-function variant. These findings highlight PTPN22 as a novel regulator of dectin-1 signals, providing a link between genetically conferred perturbations of innate receptor signaling and the risk of autoimmune disease.