Immunochemistry of the Lewis blood-group system. III. Studies on the molecular basis of the Lex property.

The antigen specificities of different anti-Lex sera were examined by immunoadsorption studies using adsorbents with well-defined carbohydrate units covalently bound to an inorganic matrix (Synsorb, Chembiomed). In contrast to those of normal anti-Lea and anti-Leb sera, the antibody binding site of Lex antibodies was found to be considerably smaller, comprising merely the structure Fuc alpha leads to 4GlcNAc--R. Based on this property, homogeneously recting Lex antibodies could be isolated from heterogeneous anti-Lea + b + x sera by means of affinity chromatography of Fuc alpha leads to 4GlcNAc-Synsorb. When the serological reactivity of the purified Lex antibodies against a Lea-active glycolipid isolated from human plasma was compared with that of normal anti-Lea serum using haemagglutination inhibition and quantitative passive haemagglutination tests, evidence was obtained that the Lex character of cord blood erythrocytes is not based on the existence of a separate Lex antigen, but rather on the ability of the anti-Lex antibodies to react already with traces of Lea substance present on fetal erythrocytes, not detectable by normal anti-Lea agglutinins.