Immune response of mice to Thy 1.1 antigen: genetic control by alleles at the Ir 5 locus loosely linked to the H 2 complex

The primary response of mice to Thy 1.1 antigen was measured by means of a plaque assay detecting cells which produce antibodies lytic for AKR thymocytes. It was found that F₁ hybrids between the low responder strains C57BL/6J, C57BL/10J, or B10.T and the DBA/2J strain produced significantly more plaque forming cells per spleen than either parental strain. In backcross populations of these three F₁ hybrids to C57BL/6J, C57BL/10J, or B10.T parents, 16.1 to 21% of H 2 heterozygotes were low responders as was the H 2 homozygous parent. These low responder H 2 heterozygotes, when mated to the C57BL/6J parent, produced 70.2% low responder H 2 heterozygotes, whereas when mated to the DBA/2J parent they produced only 5.7% low responder H 2 heterozygotes. The data obtained were interpreted as evidence for the existence of the locus designated Ir 5, which participates in the control of the immune response to the Thy 1.1 antigen together with loci belonging to the I region of the H 2 complex designated Ir Thy 1. From the recombination frequency between the Ir 5 locus, the H 2 complex, and the T locus in the (B10.T x DBA²/J)F₁ x B10.T backcross population, the relative position of the Ir 5 locus has been estimated. This locus falls about 19 map units to the right of the H 2 complex.