Immunochemical Studies on Blood Groups

Abstract

Summary The nondialyzable residue of mild acid treated blood group A or B substance (P1 fractions) can give rise in human beings to precipitins specific for the A P1 and B P1 fractions respectively. A P1 fractions differ from untreated A substance in that they are able to stimulate the formation of A P1 specific precipitins in group A as well as group O individuals. Similarly B P1 fractions differ from untreated B substance since they may give rise to B P1 specific precipitins in group AB as well as group O subjects. Anti-B P1 precipitins are specific for groupings present in B substance which are exposed by mild acid hydrolysis since untreated B preparations show little or no reactivity with anti-B P1 sera but acquire this capacity following mild acid treatment. Hog A substances likewise show no capacity to remove anti-A P1 precipitins unless subjected to mild acid treatment. A single human A substance tested, however, was found to possess A P1 specificity prior to treatment. Quantitative oligosaccharide inhibition studies indicate that B P1 specificity is partially determined by terminal nonreducing α-galactosyl residues. These α-galactosyl determinants of B P1 specificity appear to be involved in a linkage different from that of α-galactosyl determinants of blood group B specificity since melibiose which is very effective in inhibiting B-anti-B precipitation, is a poor inhibitor of B P1 anti-B P1, being even less effective in this system than galactose. Thus the galactosyl residues of B P1 determinant groupings are probably not in 1 → 6 linkage. Limited inhibition studies show anti-A P1 to differ in specificity from anti-A since N-acetyl-glucosamine is able to inhibit A P1-anti-A P1 precipitation but shows no inhibitory effect on A-anti-A precipitation. The ability of B and B P1 fractions to precipitate anti-B is independent of the capacity of the same preparation to remove anti-B P1 precipitins. In agreement with inhibition studies this suggests that groupings determining B P1 specificity are distinct from those groupings conferring blood group B activity. In addition, time-hydrolysis studies of human B substance at pH 1.62, 1.32 and 1.10 show that reactivity with type XIV horse antipneumococcal sera as well as reactivity with human anti-B and anti-B P1 sera are affected in a different way for each specific antiserum further indicating distinct structural groupings to be associated with B, B P1 and type XIV cross reactivity.