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This study describes a novel MHC class I mouse mutant that was discovered because of loss of reactivity of its cells to monoclonal antibodies. The mutation occurred in the H-2Ks molecule and is the first in vivo mutation described that has a single altered amino acid residue (amino acid 107) distant from the regions considered to be peptide or TCR contacts. Nevertheless, skin grafts from the mutant to the parent are rejected by CD8+ T-cells. In the reciprocal direction, the mutant shows partial tolerance to parental skin grafts, suggesting that the mutant is inefficient in selecting alloreactive T-cells specific for the wild-type Ks molecule.

The immunization of selected congenic strains and hybrids with the Ea-2.1 cellular alloantigen of the mouse shows that the anti-Ea-2.1 immune response is regulated by a gene or genes associated with the H-2 gene complex. It was earlier demonstrated that H-2r and H-2b were, respectively, responder and nonresponder haplotypes. In this report it is shown that the haplotypes H-2d and H-2g2 are also responder haplotypes, while H-2a, H-2k, H-2m, H-2p, H-2q, H-2awl and H-2u are nonresponder haplotypes. The responder H-2g2 and nonresponder H-2awl haplotypes are recombinant configurations that map the Ea-2.1 regulator gene, or genes, within or adjacent to the I-A subregion of the H-2 gene complex.