Charge differences between human IgG isoantibodies associated with specificity.

Human sera containing various blood group antibodies were fractionated on carboxymethylcellulose, using stepwise elution, and fractions were assayed for total IgG concentration and for antibody titre. Whereas the highest concentration of total IgG was regularly found in the 0.06 M phosphate fraction, the highest titres of anti-D, anti-E and anti-Fy were found in the 0.1 and 0.15 M fractions indicating that these antibodies are less negatively charged than the bulk of the IgG. In two cases in which the concentration of anti-D was estimated with radioiodine-labelled antiglobulin, the amount in the 0.15 M fraction, as a percentage of total IgG present, was respectively eight and seventeen times higher than in whole serum. With the Rh antibodies anti-c and anti-e, the difference from total IgG in elution pattern was less striking, the antibodies being found mainly in the 0.06–0.1 M fractions. Finally, the distribution of anti-K, anti-A and anti-B in the different fractions did not differ from that of total IgG.