The cross-reacting antibodies of group O sera: immunological studies and possible explanation of the observed facts.

Eluates were prepared from fifteen group O sera using A and B red cells. The sera originated from group O women who had either A or B children. In eight of the chosen sera, anti-A was the immune antibody and in seven, the anti-B. Antibody cross-reacting with both A and B red cells was found in all the eluates. The results of titrations of cross-reacting antibody eluted from the red cells, both before and after absorption with A or B red cells and group specific substances, all indicate that the cross-reacting antibody produced by stimulation with antigen A is different from that produced by B. The work also includes experiments using A, A and A red cells in conjunction with an immune group O serum chosen because of its good reactivity with A and A cells. It is particular interest that potent eluates from this serum prepared from A cells failed to agglutinate cells of A slightly less potent eluates from group B agglutinated A to a titre of 128. Two types of cross-reacting antibodies are postulated depending upon whether they are produced in response to stimulation by A or B. It is thought that most of the cross-reactive antibodies are directed against common portions of the blood group active oligosaccharide side chains, including the substituent at carbon atom 2 of the terminal non-reducing sugar (A (NH.CO.CH) or B(OH) specificity). Denaturation or alteration of the spatial configuration of the antibody molecules after dissociation from the antigen may account for some of the observed phenomena.