To explore the effect of HLA-DRB5 on ITP, we knocked down HLA-DRB5 in ITP mice through tail vein injection with sh-HLA-DRB5 adenovirus, which resulted in the decreased HLA-DRB5 mRNA and protein expressions in ITP mice (Figure 2a–c, p < 0.001). This evidence concerns the gene HLA-DRB5 and autoimmune thrombocytopenic purpura.