Abstract: Objective To identify the expression level and clinical significance of plasma sCXCL16 in adult primary immune thrombocytopenia (ITP). Methods From December 2016 to December 2018, patients diagnosed with ITP at our hospital outpatient clinic were selected, including 46 active ITP, 42 ITP in remission and 40 health control group. The expression level of plasma sCXCL16 was detected by enzyme-linked immunosorbent assays (ELISA), and platelet (PLT) count, proportion of CXCR6 expression on lymphocyte subsets, CXCL16 and CXCR6 mRNA expression levels in peripheral blood mononuclear cells(PMBC) were detected respectively. Then, correlation of plasma sCXCL16 with disease course, bleeding and PLT were analyzed. Results Plasma sCXCL16 levels in active ITP patients were significantly higher than those in control group（P<0.05）and of patients in remission（P<0.05）, while PLT count in active ITP patients was significantly lower than that in the control group（P<0.05）and of patients in remission（P<0.05）. The proportion of CXCR6 expressed on CD4+ T cells, CD8⁺ T cells, and B cells in active ITP patients was significantly higher than that in control group and of patients in remission (P<0.05). PMBC CXCL16 mRNA and CXCR6 mRNA levels in active ITP patients were higher than those in control group and of patients in remission（P<0.05）. Plasma sCXCL16 in active ITP patients was not associated with disease course（r=-0.032, P=0.894）, nor did with PLT count（r=0.034, P=0.883）, while plasma sCXCL16 in active ITP patients was positively correlated with bleeding（r=0.532, P=0.025）; There was no correlation between plasma sCXCL16 levels and disease course, bleeding and PLT in patients with remission and normal control group（P>0.05）. Conclusion Plasma sCXCL16 levels might be involved in the pathogenesis of ITP by regulating the proportion of CXCR6 in lymphocyte subsets. It can be used as a biomarker to assess efficacy of ITP treatments.

Key words: sCXCL16, Thrombocytopenia, Lymphocyte, Platelet