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Defining the Specificity of Anti‐A/B IgM/G Antibodies with Different Antigens and Lectins 1

Abstract. The specificity of anti‐histo blood group A/B antibodies is defined by the antigen used for their production and selection (in the case of mouse monoclonal antibodies, mAbs) or by the antigens present on various intestinal bacteria (for polyclonal human IgM and/or IgG, phAbs). Absorption experiments with red blood cells and free antigen have been used earlier to define specificity; here we use A/B substances of human, animal and synthetic origin as well as known reactivities of mAbs or lectins as tools to further characterize epitope properties of the A/B antigens. The signal response patterns obtained with identical phAbs anti‐A/B IgM/G on three different antigens are superposable. In contrast, commercially available mAb anti‐A/B IgM, when tested on the same antigens, revealed different response curves. The chemical specificity of lectins for distinct monosaccharides in terminal position was exploited to delineate the specificity of mouse ascites anti‐A IgG1 and of phAbs anti‐A/B IgM/G. Helix pomatia lectin inhibited the access of MB9 to porcine A almost completely whereas binding capacities of human anti‐A IgM/G were inhibited by 50 and 62%, respectively. In similar experiments Bandeiraea simplicifolia lectin was seen to inhibit access of anti‐B IgM/G to horse B by 34 and 58%, respectively. No inhibition was seen with lectin from Ulex europaeus or concanavalin A on plates coated with the three different A or B substances. Thin‐layer chromatography (TLC) of antigens revealed one spot for the synthetic trisaccharides, whereas the human and animal blood group substances showed 2 and 3 spots, respectively. Immunostaining experiments of TLC with mAbs revealed 1 spot only per lane, suggesting a high degree of epitope homogeneity.