One (H-2D2b) of the three Db region-controlled molecules (H-2D1b, H-2D2b, H-2Lb) is not detected in bm13 mutant.

Analysis of the antigenic heterogeneity of Db region products by the technique of antibody-induced redistribution of cell surface antigens (capping) revealed the existence of two types of H-2 molecules reactive with the monoclonal anti-Db antibody, B22-249R 1 (H-2.m2). The relationship of the two H-2.2-positive molecules described here is similar to that of H-2D and H-2M detected in the products of the Dd region; they differ in the repertoire of the H-2 public specificities, although they share the private specificity. We designate them, in accordance to recently proposed nomenclature, H-2D1b and H-2D2b. Both types of molecule have been detected on T lymphocytes of C57BL/6 (H-2b), C3H.B10(H-2b), and B10.A(2R) (H-2h2, KkDb) strains. In mutant strain B6.C-H-2bm13, however, only one type of H-2.2-positive molecule, H-2D1b, could be detected. This finding resembles the situation in the d haplotype, in which mutant strain B10.D2 (M504) (H-2dm1) had only one molecule (H-2Dd), of the two H-2.4-positive molecules H-2Dd and H-2Md that could be detected. A third Db region molecule, H-2Lb, does not carry the Db private specificity H-2.2, and it is detectable by some of the antibodies against the H-2.28 family of specificities; it is distinct from the Qa-2 molecule. The H-2Lb molecule was detected in all strains tested in this experiment, including the bm13 mutant.