Crossreactivity between Qa-1 region and H-2K antigens.

Antiserum (A.TL X A.SW)F1 anti-A.TH is specific for the products of the Qa-1a region. It reacts only weakly or, under certain circumstances, not at all with the immunizing cells, but it reacts strongly with 100% of H-2f and H-2p lymphocytes. The molecules that are the target of this strong heteroclitic reactivity are controlled by a gene in the K region, most likely the K locus itself. The results are interpreted in terms of crossreactivity of Qa-1-specific antibodies with Class I major histocompatibility complex molecules. This crossreactivity underscores the relatedness of Qa and Class I loci and strengthens the argument that Qa loci are members of the Class I family.