HYBRID RESISTANCE TO PARENTAL MARROW GRAFTS: ASSOCIATION WITH THE K REGION OF H-2.

Bone marrow of homozygous C57BL/10 donors was tested for growth in x-irradiated isogenic recipient mice, in (C57BL/10 X 129) F(1) mice, and in F(1) hybrids from congenic parents differing respectively, for an allelic substitution at one of the histocompatibility loci H-1, H-2, H-3, and H-4. All the tested H-2 heterozygotes resisted the transplantation of 10(4) parental marrow cells, whereas H-2 homozygotes were nonresistant, in spite of heterozygosity, at one or several other H loci. Findings in F(1) hybrids between C57BL/10 mice and mice carrying alleles resulting from crossing-over within the H-2 locus demonstrated that the hybrid resistance was associated with heterozygosity in the K region, but not in the D region of the H-2 locus.