Evaluation and comparison of three human monoclonal anti-S, two human polyclonal anti-S, and one murine anti-GPB

Polyclonal anti-S react with Met29 of red blood cell (RBC)-bound glycophorin B (GPB) but may also require adjacent amino acids. Treatment of RBCs with certain enzymes and sodium hypochlorite-based bleach (NaClO) affect the interaction of GPB with anti-S. Some, but not all, anti-S react with hybrid glycophorin molecules associated with the TSEN antigen. The purpose of this study was to characterize monoclonal anti-S and to compare their reactivity to polyclonal anti-S in order to determine their potential as blood group reagents and research tools. Furthermore, through inhibition experiments, we attempted to define the epitope recognized by the antibodies. Three monoclonal (MS-93; MS-94; MS-95) and two polyclonal (A1958; X1960) anti-S and a monoclonal anti-GPB (Mab 148) were tested by standard hemagglutination with RBCs of known common and rare phenotype, with S+ RBCs treated with enzymes, with different concentrations of NaClO, and after incubation with synthetic peptides. The anti-S gave different patterns of reactivity. Reactivity with sialidase-treated RBCs showed that MS-93, MS-95, Mab 148, and X1960 recognize sialic acid independent epitopes, whereas MS-94 and A1958 require sialic acid for optimal reactivity. MS-95 and X1960 were strongly reactive with TSEN+ RBCs and only Mab 148 agglutinated S- Dantu+ and S- St(a+) RBCs. MS-94 and Mab-148 agglutinated S+ RBCs treated with NaClO. MS-93 was inhibited only by the 14-mer S-specific synthetic peptide whereas MS-95 was inhibited by all three synthetic peptides containing S-relevant residues. This study clearly demonstrates that different anti-S have different characteristics that should be analyzed before selecting monoclonal antibodies for the basis of reagents for use in the clinical laboratory. These anti-S, because of their varied characteristics, will be useful research tools.