Immunological Identification of Blood Group PkAntigen on Normal Human Erythrocytes and Isolation of Anti-Pkwith Different Affinity

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Abstract
The P1 and Pk blood group glycolipid antigens have the common terminal disaccharide, Gal(a,1-4)Gal, but previous studies indicated that anti-P1 from P2 individuals does not cross-react with Pk antigen. In this study the specificities of anti-P1 and anti-Pk were analyzed carefully by complement fixation and hemagglutination techniques. 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 4 p individuals. Most of the anti-P1Pk antibodies were Ig[immunoglobulin]G, but the anti-P1 from the P2 individual was IgM. 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, to make anti-Pk reagents, p sera (anti-P1PPk) were absorbed with P1 cells which contain CTH. The anti-P1Pk antibodies in p sera were separated by partial absorption with P1 erythrocytes and elution from the absorbing cells, into 2 fractions that differ markedly in their affinity for .alpha.-methyl-D-galactoside and the oligosaccharides prepared from CTH.