The frequency of OX40+CD4+T cells among CD4+T cells, the plasma concentration of sOX40L protein, and OX40 and OX40L mRNA expression levels in PBMCs were significantly increased in primary ITP patients compared with healthy controls (HCs), and their expression was involved in low platelet counts and antiplatelet autoantibodies of ITP patients. This evidence concerns the gene CD4 and autoimmune thrombocytopenic purpura.