T cell determinant mapping between K and I-A with I-region properties.

We investigated genes in the chromosomal segment between K and I-A. Recombination in strains AQR and A.TL previously established the right-hand K region and left-hand I-A subregion boundaries. This report provides evidence that strains AQR and A.TL differ in their intra-I-region crossover points; AQR has k haplotype genes between K and I-A which A.TL lacks. Using three different strain combinations, we produced antibodies specific for a T lymphocyte determinant, Iat.W41, encoded by genes in the Kk to I-Ak interval. Like A.TL, B10.MBR (an intra-I-region recombinant) lacks the Iat.W41-controlling gene. Immunofluorescence analysis and a cytotoxicity assay detected Iat.W41 determinants on mature T lymphocyte subset; thymocytes, bone marrow cells, B cells and macrophages do not express this specificity. Iat.W41-bearing lymphocytes display the Thy-1.2 antigen, but not Ly-1 or Ly-2 determinants. Iat.W41 expression is independent of non-H-2 genes. In addition to a strong mixed leukocyte reaction, genes between K and I-A contribute to a graft-versus-host reaction. The Iat.W41-controlling locus appears distinct from previously identified I-A loci.