Immunochemical studies on blood groups. XLVII. The I antigen complex--precursors in the A, B, H, Lea, and leb blood group system--hemagglutination-inhibition studies.

A partially purified blood group-like substance obtained from milk showed I activity with 2 of 21 anti-I sera. With these antisera, certain human ovarian cyst substances considered to be precursors of the A, B, H, Le(a), and Le(b) substances also showed I activity comparable to the milk material. Strong I activity could be produced by one-stage periodate oxidation and Smith degradation of human ovarian cyst A and B substances, or of hog mucin A + H substance, or by mild acid hydrolysis of human saliva or ovarian cyst blood group B substance. The two sera indicate that I specificity appears at intermediate stages in the biosynthesis of the A, B, H, Le(a), and Le(a) substances. Anti-I sera differ strikingly in their specificities, indicating substantial heterogeneity of the I determinants.