True about MHCAI-

MHC gene is present on the short arm of chromosome 6. Class II comprises DR, DQ, DP regions (A, B, C loci are present on class I). Class III consists of complement components, Mixed leukocyte reaction involves class II MHC. The histocompatibility antigens (human leukocyte antigens - HLA) are cell surface antigens that induce an immune response leading to the rejection of allografts. The principal physiologic function of the cell surface histocompatibility molecules is to bind peptide fragments of foreign proteins for the presentation of antigen-specific T cells. The histocompatibility antigens are encoded by a closely linked multiallelic cluster of genes -» Major histocompatibility complex (MHC) or Human leukocyte antigens complex (HLA complex). HLA complex of genes is located on the short arm of chromosome 6.