Estimation of the number of binding sites for a murine monoclonal anti-Lub on human erythrocytes.

The number of Lub antigen sites on the human erythrocyte membrane, as recognised by the murine monoclonal antibody BRIC-108, has been determined. The number of antibody molecules bound per cell on one example of cells of the phenotype Lu(a-b-) with recessive inheritance was an average of around 200 in replicate determinations, which probably represents non-specific antibody binding. A similar number of antibody molecules to this bound to trypsin- or pronase-treated normal cells or cells of the Lu(a-b-) phenotype associated with the inheritance of the X-borne gene, XS2. The number of binding sites on three examples of cells of the phenotype Lu(a-b-) with dominant inheritance was from 440 to 690. A variation in the number of binding sites per cell from 1,640 to 4,070 was found in five individuals with the phenotype Lu(a-b+) and from 850 to 1,820 in four individuals with the phenotype Lu(a+b+). Four individuals with the Lu(a+b-) phenotype had an average of 480 binding sites per cell. The Lub antigen therefore appears to a have low-site density and a variable level of expression on the erythrocyte surface.