Antihuman CD44 antibody BJ18 inhibits platelet phagocytosis by correcting aberrant FcɣR expression and M1 polarization in immune thrombocytopenia

Abstract Background Immune thrombocytopenia (ITP) is an autoimmune hemorrhagic disease with a low platelet count. CD44 is a pivotal component involved in phagocytosis and inflammation, and monoclonal antibodies (mAbs) against CD44 have been shown to be beneficial in several autoimmune diseases. In the present study, we investigated the correlation between CD44 levels and disease severity in patients with ITP and explored the immunomodulatory mechanisms of the antihuman CD44 mAb BJ18 on platelet phagocytosis mediated by monocytes/macrophages. Methods Plasma was collected from 45 participants to measure the circulating concentration of CD44 using ELISA. Peripheral blood mononuclear cells from patients and controls were isolated and induced to differentiate into monocytes/macrophages utilizing cytokines and drugs. CD44 expression on circulating cells and the effects of BJ18 on platelet phagocytosis, Fcɣ receptor (FcɣR) expression and M1/M2 polarization of macrophages were evaluated using flow cytometry and qPCR. Results CD44 levels of both the soluble form found in plasma and the form expressed on the surface of circulating monocytes/macrophages were significantly elevated in ITP patients. Linear correlations were verified between the CD44 levels and major clinical characteristics. In an in vitro study, BJ18 successfully inhibited platelet phagocytosis by monocytes/macrophages obtained from ITP patients. Further studies indicated that BJ18 corrected abnormal FcγR expression on monocytes/macrophages. Moreover, the polarization of proinflammatory M1 macrophages could also be regulated by BJ18. Conclusions Our data indicated that the CD44 level has potential predictive value for disease severity and that the antihuman CD44 mAb BJ18 may be a promising therapy for ITP patients.