By sensitizing human red blood cells with antisera specific for corresponding blood group antigens and subsequent rosette formation, we were able to distinguish homozygosity of the antigens from heterozygosity. Three types of rosette assays were utilized: a protein A rosette, an immunoglobulin-coated bead rosette, and an erythrocyte-antibody rosette with human lymphocytes. In the Rh blood group system, we were able to demonstrate the dosage effect of the Rho(D) antigen by rosette assay in addition to determining that the deletion of the C and/or E alleles increased the rosette forming cell count when red blood cells with different genotypes were sensitized with Rh immune globulin (anti-D). The assay proved to be reproducible in distinguishing between homozygous and heterozygous Rh red blood cell antigens, and may be adaptable to study many antigenic markers on cell surfaces.

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