Female mice of the H-2b haplotype possess a dominant Ir gene controlling H-2 restricted cytotoxic T cell responses to H-Y. This gene maps in the IA subregion, but requires appropriate associative antigens coded by K or D end genes in order for the response to be initiated and effected. Separable from the Ir gene controlling anti-H-Y cytotoxic responses in H-2b mice is a dominant Ir gene in the IB subregion and this controls the ability of female mice to reject syngeneic male skin grafts. It does not apparently require associative K/D antigens for its operation.
Mouse strains of independent haplotypes other than H-2b are nonresponders to H-Y, both with respect to the generation of H-2 restricted cytotoxic responses and to skin graft rejection. However, certain F1 hybrids (e.g. k/d, k/s, k/a, k/q, d/s) are responders in that they make cytotoxic responses to H-Y, although none of them reject skin grafts.