Epitope clusters of Qa-2 antigens defined by a panel of new monoclonal antibodies

A recently derived intra-MHC recombinant mouse strain, the C3H.KBR was found to produce a surprisingly high titer of anti-Qa antibodies when immunized with C3H.SW lymphocytes. By using this immunization combination, a panel of 10 mAb with specificity for determinants encoded by the Q region was produced. These reagents were analyzed for strain distribution by microcytotoxicity, immunofluorescence, and flow cytometry assays. Competitive inhibition analyses, performed by using fluorescein-labeled antibodies and normal spleen cells, defined at least three epitope clusters, or groups of spatially related determinants, detected by this panel. One epitope cluster was unique to this new series of antibodies in that it was not detected with seven previously described anti-Qa mAb. These antibodies also have been analyzed for reactivity with products of isolated Q-region genes by using transfected cell lines. The data indicate that the Q6d, Q7d, and Q10d genes encode determinants reactive with one or more mAb and that two of the three epitope clusters defined with normal cells map to the N and/or C2 domains of these molecules. The third epitope cluster is presumed to map to the C2 domain. These reagents should be useful in determining the number of Q-region genes expressed and in analyses of Q gene expression in subpopulations of normal cells, in transfected cell lines, and during differentiation and ontogeny.