Mononuclear macrophages ingest antigens and process them into antigen peptides. Then antigen peptides are combined with surface MHC molecules and are expressed on the cell surface, effectively presenting antigens to helper T lymphocytes. B lymphocytes also have a similar antigen presentation effect. T cells combine with MHC II/antigen to activate B cells. While the BCR of the memory B cell binds to a specific antigen, the antigen is endocytosed by the B cell. After these antigens are cut into fragments, they return to the cell membrane in a state combined with MHC molecules . T cells express CD4 or CD8 co-receptors. They recognize non-polymorphic regions of MHC protein on target cells and can bind to partial MHC protein regions . Helper T cells express CD4 and recognize MHC class II proteins, while cytotoxic T cells express CD8 and recognize MHC class I proteins . NK cells express inhibitory receptors (KIR) of MHC class I molecules. These inhibitory receptors include the human KIR (killer cell Ig-like receptor) . Another function of NK cells is recognizing and eliminating cells that cannot express their major histocompatibility complex (MHC) class I molecules . Interestingly, individuals with specific MHC alleles are less susceptible to severe forms of malaria . It means that the combination of immune cells and MHC is closely related to the susceptibility of certain diseases.