Based on ITP murine models, our current results revealed that the downregulation of HLA-DRB5 inhibits the activation of CD8+ T cells to elevate PLT count in peripheral blood of ITP mice, which could be accomplished by decreasing MHC-II-mediated antigen presentation of macrophages. The gene discussed is HLA-DRB5; the disease is autoimmune thrombocytopenic purpura.