The monoclonal xenoantibody Q6/64 recognizes a determinant expressed by certain gene products of the A and B loci of the HLA region.

A combination of serological (cytotoxicity, binding assay, lysostrip) and immunochemical (indirect immunoprecipitation, sequential immunoprecipitation, two-dimensional gel electrophoresis) assays have shown that the monoclonal antibodies Q6/64 recognizes an antigenic determinant which is expressed by certain gene products of the A and b loci of the HLA region. The determinant identified by Q6/64 is spatially close to those which define the serological polymorphism of the HLA-A, B, C antigenic system. The results presented in this study in conjunction which those recently published by other investigators indicate that sharing of determinants among HLA-A and -B allospecificities is more frequent than originally assumed on the basis of the cross-reactivity pattern obtained with alloantisera. This conclusion is in agreement with the high degree of homology in the primary amino-acid sequence of A and B allospecificities.