PDCD1 and polymyositis: Multicolour immunohistochemical staining showed increased CD4+, FOXP3+CD4+, TIM3+CD4+ cells and exhausted Tregs (TIM3+FOXP3+CD4+ cells) in the skeletal muscles of patients with DM (all P < 0.05), and increased PD1+CD4+ cells and exhausted Tregs (PD1+FOXP3+CD4+ cells) in patients with PM (all P < 0.05) compared with the NG (Figure 5A,B).