Antibodies to histo‐blood group substances A and B: agglutination titers, Ig class, and IgG subclasses in healthy persons of different age categories

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Abstract
Isotypes and IgG subclasses of ABO antibodies from sera of 235 healthy blood donors were determined by an enzyme‐linked immunosorbent assay (ELISA). Synthetic A and B trisaccharide‐bovine serum albumin glycoconjugates were used for coating and monoclonal antibodies for the detection of heavy chain isotypes. Hemagglutination titers were determined in addition. Blood donors were between 20 and 67 years old, and at least 10 sera per 10‐year age category and ABO blood group were included in this study. Antibody concentrations were expressed as a percentage of an internal standard, and sera with subclass‐restricted anti‐A and/or anti‐B (anti‐A/B) responses were used to normalize the ELISA values of IgG subclasses. A good correlation between the sum of the four subclasses and the total anti‐A/B IgG values (rs = 0.81 for anti‐A and 0.84 for anti‐B) was obtained. IgG1 and IgG2 were the most predominant subclasses, but were found in various proportions in different individuals. Donor‐to‐donor variation exceeded age‐related changes for all measured parameters. The correlation of anti‐A IgM, IgG, IgA, and their sum with the agglutination titers was significant and revealed rs values of 0.70, 0.65, 0.65, and 0.80, respectively. For anti‐B as well, the correlation of ELISA values with the agglutination titer was best when all three isotypes were added. We conclude that anti‐A/B IgA, together with IgM and IgG, substantially contributes to the agglutination reaction. Potentially autoreactive antibodies were detected in sera of blood groups A, B, and AB.