The relationship betweeen the h-2 loss mutations of h-2da and h-2db in the mouse.

The mouse strain BIO.D2-H-2 aa carries the mutant H-2 aa allele, derived after chemical induction, and this has been shown to be a gain and loss mutation involving the H-2D a locus. BALB/c-H-2 ab, derived spontaneously, is a loss mutation only, and appears not to involve the H-2D a, but rather the H-2L a locus. The two mutations effect both graft rejection and serologically detected H- 2 specificities (Type II mutation). In the experiments described in this study, the loss mutations in the H-2 aa and H-2 ab mutants have been compared by skin grafting, and by direct and absorption serological techniques: (1) By skin grafting, using the well established complementation method, it has been shown that H-2 aa and H-2 ab do not complement each other, i.e., the mutation in both occurred at the same 'locus.' However, by appropriate selection of donor and recipient, it has become clear that 1)-2 aa had a greater loss than did H-2 ab, although H-2 da includes the loss found in H-2 ab. (2) Serological studies have demonstrated that H-2D.4 was altered in H-2 da, but not in H-2db; 'H-2.28' (detected by D-28b and D-29) was decreased or lost in both mutants; H-2 db anti- BALB/c failed to react with H-2da; both mutants reacted similarly with D-28 sera. In addition, sera made using H-2 d~ as donor did not contain an anti-H-2.28 antibody. The loss mutation involving H-2 da therefore appears to have led also to the loss of H-2.28 as found in H-2 d~. We conclude that the H-2 a" strain arose after a complex mutation or recombination event which involved both the H-2D a locus and the closely linked H-2L d locus, whereas H-2 db affects only the H-2L locus.