The H-2 Major Histocompatibility Complex and the/Immune Response Region: Genetic Variation, Function, and Organization

One of the most rapidly developing areas of immunologic research deals with the H-2 gene complex, a tightly linked series of genes controlling a variety of immunologic traits, including histocompatibility and immune responsiveness. This chapter summarizes the varieties of phenotypic traits associated with differences in the H-2 complex. The mapping of the H-2 complex into four major regions marked by H-2K, Ir-1, Ss-Slp, and H-2D genes plus the associated Tla gene is discussed in the chapter, along with the phenotypic traits associated with these regions. The chapter discusses the immune response region, the genes of which appear to control a variety of immune phenomena—including antibody response to many antigens, susceptibility to tumor viruses, and graft-versus-host (GVH), and mixed lymphocyte culture (MLC) reactions. The H-2 complex consists of many genes with diverse functions, most of which control cell membrane structures and/or processes. The fact that lymphocytes are particularly affected by H-2 genes has important implications for immunology. However, some of the genes also affect other cell types, implying a still larger role for the H-2 complex, perhaps in development or in cell regulation. Because the H-2 complex is the most thoroughly characterized segment of a mammalian chromosome, it is also an important model for the studies of gene action, organization, and evolution in mammals.