[Studies on properties of cross-reacting anti-A,B antibodies in group O sera]

It is widely accepted that the sera of group O individuals contain three antibodies: anti-A, anti-B, and an antibody capable of reacting with both A and B red cells, generally called anti-A,B. The exact nature of the anti-A,B antibody, however, has been controversial for a long time. This paper attempts to answer the question of the anti-A,B antibody. The anti-A,B antibody was separated and purified from pooled group O sera by six consecutive runs of affinity chromatography on alternating columns of group A-specific and group B-specific immunoadsorbents. The final eluate, the anti-A,B preparation, was found to be homogeneous in the polyacrylamide gel disc electrophoresis and immunoelectrophoresis. Immunodiffusion studies, together with treatment with 2-mercaptoethanol, showed the anti-A,B antibody to be IgG. The anti-A activity of the anti-A, B antibody was inhibited with group A secretor saliva and group A-specific substances, but not with group B secretor saliva and group B-specific substances, and the anti-B activity of the antibody was inhibited with group B secretor saliva and group B-specific substances, but not with group A secretor saliva and group A-specific substances. Then, Fab fragments of the anti-A,B antibody were prepared by papain digestion. Indirect hemagglutination tests for the Fab fragments by use of an anti-Fab antiserum demonstrated that the Fab fragments possess both of anti-A and anti-B activity. Then, rosetting tests for the anti-A,B antibody were carried out using A- and B-specific trisaccharides covalently attached to silica particles. The results showed that the anti-A,B antibody linked A- and B-specific trisaccharides to A and B red cells. These results strongly indicate that the anti-A,B antibody is an antibody with significant affinity for both group A and group B antigens rather than an antibody directed against a structure common to group A and group B antigens. The conclusions based on the above experiments are that the anti-A,B antibody in group O sera is IgG and presumably possesses dual specificity regarding to anti-A and anti-B activity.