Monoclonal antibodies against glycophorins

Glycophorins of human erythrocytes have been extensively studied and the structure of three of them is fully (glycophorins A and C) or almost fully (glycophorin B) known [1, 2]. Glycophorins span the erythrocyte membrane and their NH₂-terminal domains exposed at the cell surface are heavily glycosylated. Glycophorin A occurs in two genetically determined forms carrying at NH₂-terminal end blood group M and N antigenic determinants. Glycophorin B (blood group Ss glycoprotein) has the structure of NH₂-terminal region (a.a. residues 1–26) identical to glycophorin A of blood type N, and also shows a high degree of homology with glycophorin A in the internal portion of the molecule, whereas glycophorin C has a different amino acid sequence. The knowledge of structure and orientation in the membrane and genetic differentiation of glycophorins facilitate elucidation of the fine specificity of anti-glycophorin antibodies.

The 30 anti-glycophorin-antibodies obtained were tested by agglutination of untreated and modified erythrocytes, immunoblotting, and binding to glycophorin A in microtiter plate ELISA. Moreover, inhibition of antibodies by untreated and modified glycophorin A preparations was studied. The methods used were described in detail in our recent publications [3, 5].

The antibodies could be divided into groups (Table I), depending on specificity. The 19 antibodies recognized epitopes located at the NH₂-terminal end of glycophorin A that could be easily shown by specific or distinctly preferable reactivity with blood group M (8 MoAbs) or N (11 MoAbs) antigen. The antibodies with anti-N specificity also reacted with glycophorin B. Among the remaining blood group MN-unrelated antibodies, 4 were specific for glycophorin A, 3 recognized epitopes common for glycophorins A and B, 2 reacted to glycophorin C, and the specificity of 2 antibodies could not be clearly established. The antibodies in each group differed in sub-specificity and antigen-binding properties.