Idiotypic specificities of anti-Rh antibodies.

Idiotypic antibodies were produced in rabbits to Rh antibodies isolated from the serum of an individual with high Rh antibody titer. These antisera after absorption with blood IgG failed to react with immunoglobulins lacking anti-Rh activity. They agglutinated cells coated with the immunizing antibody to high titers. Two other anti-Rh coats out of 22 tested also were agglutinated but to considerably reduced titers indicating a degree of anti-Rh cross specificity. Four other antisera made to red cells coated with different anti-Rh antibodies showed definite but weaker idiotypic specificity. Both the idiotypic and cross-idiotypic antigens of the Rh antibodies were completely blocked when univalent fragments of the Rh antibodies were bound to antigen on the red cell.