CD274 and musculoskeletal system disorder: M2c macrophages can also induce immune tolerance by expressing inhibitory ligands such as PD-L1 to inhibit the activation and proliferation of T cells (68).Therefore, abnormal M1/M2 macrophage ratios may disrupt immune balance, leading to excessive activation or suppression of the immune system and, consequently, musculoskeletal diseases (17, 54).