Specificity of human antibodies against gal?1-3gal carbohydrate epitope and distinction from natural antibodies reacting with gal?1-2gal or gal?1-4 gal

Abstract

Antibodies against galactosyl-α1-3-galactose epitopes were characterized in normal and patient sera by radioimmunoassay binding to mouse laminin and oligosaccharide inhibition. Binding was strictly dependent on α-linked galactose in a terminal position. Reduced affinities were observed for digalactoses with α(1-2)-, α(1-6)- and α(1-4)-linkages and for the blood group B epitope, Galα1-3(Fucα1-2)Gal. Conformational models of various active and inactive oligosaccharides provided a clearer picture of the epitope requirements for the observed antibody specificity. Some antibody heterogeneity was detected by comparing individual sera and by hapten elution from a laminin adsorbent. New assays were developed with synthetic Galα1-3Gal-albumin conjugates and these were shown to be more sensitive than assays with mouse laminin. Two more ubiquitous human antibodies could be detected with Galα1-2Gal and Galα1-4Gal conjugates. They were distinct from Galα1-3Gal-specific antibodies as shown by carbohydrate inhibition. This demonstrates a considerable diversity in the recognition of α-linked galactose epitopes by natural antibodies.