A public antigenic determinant in the HLA-B5 cross-reacting group--a basis for cross-reactivity and a possible link with Behcet's disease.

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 B5 cross-reactive group (i.e., HLA-B5, B15, B18, and Bw35), we initiated a study of the chemical basis of cross-reactivity among this group of antigens. Using classic serologic procedures, an 125I-Protein A binding assay, and chemical immunoprecipitation techniques, we have defined a new antigenic determinant, tentatively designated "Y," which is present on certain HLA-B molecules. By a series of sequential immuno-precipitation experiments, Y was shown to be a "public" antigenic determinant distinct from the "private" determinants B5, B15, B18, and Bw35, but present on the same 44,000 dalton glycoprotein molecules. Although B5 is most highly associated with Behcet's disease, other members of the B5 cross-reactive group have also been associated with Behcet's, albeit to a lesser extent. These associations suggest that determinant Y may play a role in predisposition to Behcet's disease.