Immunochemical analysis of class II molecules expressed by a human B cell line with the unusual class II genotype,...

The human B lymphoblastoid cell line FPA was established from a consanguineous individual homozygous for the unusual serologically defined Class II genotype, DR5+, MB1+, (MB3-), MT2+. The MB1 allodeterminant is classically found only in association with DR1, 2, or w6 and DR5 is almost invariably associated with MB3. Class II molecules expressed by this unusual DR5 homozygous cell line have been characterized by immunochemical analysis using two-dimensional gel electrophoresis. These molecules were isolated from the FPA cell line by anti-DR5, anti-MT2, and anti-MB1 allosera, as well as a monoclonal antibody which defines an MB1-like determinant. However, an anti-MB3 alloserum and a monoclonal antibody which defines an MB3-like determinant did not immunoprecipitate Class II molecules from FPA. These studies document that the MB1 allodeterminant resides on DS molecules from this DR5 cell line and provide additional evidence that MB1 and MB3 are alleles of the same Class II antigen system.