New complexities at the Qa-1 locus.

Mouse strain and tissue distribution analyses indicate that the new antiserum A anti-A-Tlab recognizes the cell-surface product governed by the previously serologically undetectable Qa-1b allele. This cell-surface product has therefore been called Qa-1.2. Three levels of anti-Qa-1.2 cytotoxicity in the presence of complement have been observed: high, intermediate, and zero lysis. In general, high levels of lysis correlate with the presence of the Qa-1b allele, while zero levels of lysis correlate with the presence of the Qa-1a allele. The A.CA strain reacts with both anti-Qa-1.1 and anti-Qa-1.2 and may possess a third allele, Qa-Id. Several strains including B6-H-2k react in an intermediate fashion. Recombinant strain analyses indicate that this intermediate reaction may be due to modifying genes within the H-2D region.