IMMUNOLOGICAL IDENTIFICATION OF BLOOD-GROUP PK ANTIGEN ON NORMAL HUMAN-ERYTHROCYTES AND ISOLATION OF ANTI-PK WITH DIFFERENT AFFINITY

Abstract. The P1 and Pk blood group glycolipid antigens have the common terminal disaccharide, Gal(α, 1–4)Gal, but previous studies indicated that anti‐P1 from P2 individuals does not cross‐react with Pk antigen. In this paper, the specificities of anti‐P1 and anti‐Pkwere analyzed carefully by complement fixation and hemagglutination techniques and the following results were obtained: (1) Anti‐P1 from P2 serum was not absorbed with the Pk glycolipid (CTH), but this antigen absorbed all anti‐P1 and anti‐Pk (anti‐P1Pk) antibodies from the sera of four p individuals. Most of the anti‐P1Pk antibodies were IgG, but the anti‐P1 from the P2 individual was IgM. (2) The Pk antigen on normal P2 erythrocytes was not ‘cryptic’. It was reactive with p serum from which the anti‐P antibodies were removed by absorption with the P glycolipid (globoside). This was not appreciated previously because, in order to make anti‐Pk reagents, p sera (anti‐P1PPk) were absorbed with P1 cells which contain CTH. (3) The anti‐P1Pk antibodies in p sera were separated by partial absorption with P1 erythrocytes and elution from the absorbing cells, into two fractions that differ markedly in their affinity for α‐methyl‐D‐galactoside and the oligosaccharides prepared from CTH. © 1979 Blackwell Publishing Ltd