elimination of transformed cells that must display self-MHC antigens to be destroyed by effector T cells.This requirement that both the foreign antigen and the host MHC antigen be present is known as MHC restriction. Structure of Class Il Antigens 20 tom B peptide chain 28,000 daltons Carbohydrate mor rcrophages epithe R99999999898R998998 BBB88888888888888g 0 Class II antigens are glycoproteins co onsisting of two n covalently linked alpha and beta peptide chains with molecular weights of 32 and 28 kD.respectively Each chain contains two extracellular domains,a connecting peptide,a tansmembrane region,and a cytoplasmic tail.The I region is divided into five subregions (A,B,J,E,and C) with eight alleles encoding class II antigens arranged on chromosome 17.These antigens are involved in a number of immunological events. Antigen-presenting cells(APC)display I region antigen(Ia),in a restricted manner analogous to MHC restriction.The T helper cell and B cells or T cytotoxic cells and between T suppressor cells and other T cells.Delayed-type hypesensitivity is also controlled in large measure by I region gene products.Thus class II molecules are concerned with recruitment of T helper,T suppressor,and T delayed hypersensitivitit cells.Many genes of the I region and their subregions and subdivisions dramatically influence our ability to mount an immune response to an antigen.Consequently,they are referred to as immune response (Ir)genes.elimination of transformed cells that must display self-MHC antigens to be destroyed by effector T cells. This requirement that both the foreign antigen and the host MHC antigen be present is known as MHC restriction. Class II antigens are glycoproteins consisting of two noncovalently linked alpha and beta peptide chains with molecular weights of 32 and 28 kD, respectively Each chain contains two extracellular domains, a connecting peptide, a tansmembrane region, and a cytoplasmic tail. The I region is divided into five subregions (A,B, J, E, and C) with eight alleles encoding class II antigens arranged on chromosome 17. These antigens are involved in a number of immunological events. Antigen-presenting cells (APC) display I region antigen (Ia), in a restricted manner, analogous to MHC restriction. The T helper cell and B cells or T cytotoxic cells and between T suppressor cells and other T cells. Delayed-type hypesensitivity is also controlled in large measure by I region gene products. Thus class II molecules are concerned with recruitment of T helper, T suppressor, and T delayed hypersensitivitit cells. Many genes of the I region and their subregions and subdivisions dramatically influence our ability to mount an immune response to an antigen. Consequently, they are referred to as immune response (Ir) genes