Co-inhibition of LMP2 and LMP7 inhibited macrophage phagocytosis, downregulated FcγI in ITP mice, decreased FcγIII in ITP patients, inhibited T cell activation and Th1 differentiation, and alleviated thrombocytopenia in the passive ITP models. Here, PSMB9 is linked to autoimmune thrombocytopenic purpura.