Degenerate binding of immunogenic peptides to HLA-DR proteins on B cell surfaces.

Binding of linear fragments of protein antigens to class I or class II molecules of the MHC is necessary for the stimulation of a cellular immune response. This report describes the binding of a biotinylated T cell determinant from influenza hemagglutinin to class II proteins on the surface of Epstein-Barr virus-transformed B lymphocytes. The rapid, simple, and quantitative binding assay involves flow cytometric analysis of transformed B cells stained with fluoresceinated streptavidin following incubation with the biotinylated peptide. Binding of the biotinylated peptide required cell surface expression of human class II molecules, and was inhibited by an anti-HLA-DR monoclonal antibody as well as the unbiotinylated natural determinant. Rates of association and dissociation of the peptide were similar to those reported for purified MHC class II proteins, and the peptide bound only approximately 1% of the DR molecules expressed on the cell surface. When assayed on many different DR-homozygous B cell lines, the biotinylated hemagglutinin T cell determinant bound to HLA-DR on each cell line. The degeneracy of peptide binding to B cell lines was not unique to the hemagglutinin peptide because three other biotinylated T cell determinants failed to bind to class II deficient B-lymphoblastoid cells but bound to varying degrees to multiple DR-homozygous lines.