MHC

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].