Abstract
Serologic cross-reactivity among allelic gene products commonly occurs in the HLA complex, but the molecular basis of these serologic phenomena is incompletely characterized. Because of strong cross-reactivity among antigens comprising the B7 cross-reactive group (i.e., HLA-B7, Bw22, B27, B40, and Bw42) and because of the association of several antigens of this group with spondyloarthropathies, we initiated a study of the chemical basis of cross-reactivity among this group of antigens. Using classic serologic procedures, 125I-Protein A binding assay, and chemical immunoprecipitation techniques, we have defined a new antigenic determinant, tentatively designated "X", which is present on certain HLA-B molecules. By a series of sequential immunoprecipitation experiments, X was shown to be a "public" antigenic determinant distinct from the "private" determinants B7, Bw22, B27, and B40, but present on the same 44,000-dalton glycoprotein molecules. The implications of this finding regarding disease predisposition and HLA typing as a diagnostic aid are discussed.