On naming H2 haplotypes: Functional significance of MHC class Ib alleles

George D. Snell began defining and naming the H2 haplotypes many years ago by histogenetic typing. Since then, a few haplotypes have been given an additional letter, such as be for strain 129, to show that they are minor variants from the prototype (b). But by and large, differences in nonclassical class I antigens have been known (only?) to those in the field without being acknowledged by a separate haplotype symbol. Thus, strains BALB/c and NZB/B1NJ are both considered H2(d) and strains C3H/HeJ and B1O.BR are both called H2(k), although each pair differs in the TL and Qa1 antigens. In parallel with the interest in nonclassical class I antigens, the need for an appropriate haplotype nomenclature is growing. The haplotypes that require splitting are b, d, k, q, and s; the symbol be should be retained and used, and, for the other haplotypes, the suffix 2 denotes a Qa1^a haplotype with highly TL-positive thymocytes.