The relationship between theH-2 loss mutations ofH-2(da) andH-2 (db) in the mouse.

The mouse strain B10.D2-H-2(da) carries the mutantH-2(da) allele, derived after chemical induction, and this has been shown to be a gain and loss mutation involving theH-2D(d) locus.BALB/c- H-2(db), derived spontaneously, is a loss mutation only, and appears not to involve theH-2D(d), but rather theH-2L(d) locus. The two mutations effectboth graft rejection and serologically detected H-2 specificities (Type II mutation). In the experiments described in this study, theloss mutations in theH-2(da) andH-2(db) 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 thatH-2(da) andH-2(db) 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 thatH-2(da) had a greater loss than didH-2(db), althoughH-2(da) includes the loss found inH-2(db). (2) Serological studies have demonstrated that H-2D.4 was altered inH-2(da), but not inH-2(db); '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 withH-2(da); both mutants reacted similarly with D-28 sera. In addition, sera made usingH-2(da) as donor did not contain an anti-H 2.28 antibody. The loss mutation involvingH-2(da) therefore appears to have led also to the loss of H-2.28 as found inH-2(db). We conclude that theH-2(da) strain arose after a complex mutation or recombination event which involvedboth theH-2D(d) locus and the closely linkedH-2L(d) locus, whereasH-2(db) affects only theH-2L locus.