Evidence for a third,Ir-associated histocompatibility region in theH-2 complex of the mouse

Abstract

Skin grafts transplanted from B10.HTT donors onto (A.TL × B10)F1 recipients are rapidly rejected despite the fact that the B10.HTT and A.TL strains should be carrying the sameH-2 chromosomes and that both the donor and the recipient contain the B10 genome. The rejection is accompanied by a production of cytotoxic antibodies against antigens controlled by theIr region of theH-2 complex. These unexpected findings are interpreted as evidence for a third histocompatibility locus in theH-2 complex,H-2I, located in theIr region close toH-2K. The B10.HTT and A.TL strains are postulated to differ at this hypothetical locus, and the difference between the two strains is explained as resulting from a crossing over between theH-2 t1 andH-2 s chromosomes in the early history of the B10.HTT strain. TheH-2 genotypes of the B10.HTT and A.TL strains are assumed to beH-2K s Ir s / k Ss k H-2D d andH-2K s Ir k Ss k H-2D d , respectively. Thus, theH-2 chromosomes of the two strains differ only in a portion of theIr region, including theH-2I locus. The B10.HTT(H-2 tt) and B10.S(7R)(H-2 th) strains differ in a relatively minor histocompatibility locus, possibly residing in theTla region outside of theH-2 complex.