Abstract
One of the most critical interactions that initiate an immune response is the genetically determined signal provided by molecules encoded by the major histocompatibility complex (MHC) of genes. The human MHC, termed the HLA region, includes HLA Class I (classic transplantation) genes as well as HLA Class II genes, the primary genetic regulators of the immune response. The concept that HLA Class II genes regulate responsiveness is relatively new, evolving from studies in the late 1960s and early 1970s demonstrating that certain strains of animals failed to respond to particular antigens to which other members of the species could respond. . . .