Serological and Functional Evidence for Further Subdivision of the I Regions of the H-2 Gene Complex

The I-region-associated (Ia) lymphocyte antigens were initially detected as a result of efforts to serologically detect and define the products of the immune response (Ir) genes of the I region of the H-2 gene complex (see Shreffler and David 1975). Following their discovery, the serological definition of the Ia antigens proceeded rapidly. To date, 22 discrete la antigenic specificities have been defined. The distribution of these specificities by H-2 haplotype is summarized in Table 1.