Interleukin-37 reduces inflammation and impairs phagocytosis of platelets in immune thrombocytopenia (ITP).

Immune thrombocytopenia (ITP) is an autoimmune disease characterized by low platelet count with heterogeneous bleeding manifestations. Severe bleeding in ITP is not completely related with low platelet count. Fcγ receptor (FcγR)-mediated platelet destruction is one of the major mechanisms of ITP. Interleukin-37 (IL-37) is a fundamental natural suppressor of innate immunity and inflammatory responses in several autoimmune diseases. However, the role of IL-37 in the pathogenesis of ITP is unknown. In the present study, we identified that IL-37 expression was elevated in ITP patients, which was correlated with platelet count and the severity of bleeding in ITP, indicating that IL-37 could be a candidate in evaluating disease severity of ITP. In the in vitro study, IL-37 initiated an anti-inflammatory effect on monocytes/macrophages from ITP patients by down-regulating the phosphorylation of MAPK, AKT, and NF-κB signaling pathways. Moreover, IL-37 restored the balance of activating and inhibitory FcγRs and decreased antibody-mediated platelet phagocytosis by monocytes/macrophages. Our findings suggest that IL-37 may be a promising indicator of the disease severity and supplementation of IL-37 may be therapeutically beneficial for ITP patients.