MHC 是一组编码蛋白质的基因，这些蛋白质被转移到细胞表面，将细胞内或细胞外、自身或非自身抗原呈递给免疫系统的细胞，从而帮助 T 细胞区分自身和非自身蛋白质，并启动适应性免疫反应。MHC 可分为 3 个亚型，MHC I，MHC II 和 MHC III，其中 MHC I 呈递内源性抗原（例如由病毒感染的细胞或肿瘤细胞产生的抗原）以激活细胞毒性 T 细胞（CD8 + T细胞）；MHC II 呈递外源性抗原（例如细菌或寄生虫）以激活辅助性 T 细胞（CD4 + T 细胞）；MHC III 不直接参与抗原呈递，但涉及免疫调节，炎症反应和细胞信号传导。MHC 对干细胞移植（SCT）至关重要，可能导致移植物抗宿主病（GVHD）。
MHC is a group of genes encoding proteins which are transferred to the cell surfaces to present the intracellular or extracellular, self or non-self antigens to the cells of the immune system, thereby helping T cells in differentiating self from non-self proteins, and initiating adaptive immune responses. MHC can be divided into 3 subtypes, MHC I, MHC II and MHC III, in which MHC I presents endogenous antigens (such as antigens produced by virus-infected cells or tumor cells) to activate cytotoxic T cells (CD8+ T cells); MHC II presents exogenous antigens (such as bacteria or parasites) to activate helper T cells (CD4+ T cells); MHC III does not directly participate in antigen presentation, but involves in immune regulation, inflammatory response and cell signaling. MHC is crucial for stem cell transplant (SCT), and could lead to graft-versus-host disease (GVHD)[1][2].