Demonstration of rheumatoid factor in tissue by mixed agglutination with tissue sections

The mixed agglutination procedure was applied to sections of synovial tissue from patients with rheumatoid arthritis. The tissues were examined with three test systems: 1) Sheep erythrocytes sensitized by rabbit antiserum, 2) human O Rh‐positive (CD) erythrocytes sensitized by anti‐Rh serum “Ripley,” and 3) rabbit erythrocytes sensitized with mercaptoethanol‐treated pooled human serum. Adsorption of the sensitized cells to the tissue sections was obtained in most of the cases. This mixed agglutination was inhibited by denatured Γ‐globulin and by antibodies to γM, indicating that the reaction depended on RF bound in the synovial tissue. Of 31 patients with rheumatoid arthritis, tissue from 30 gave positive reactions. Tissue from many patients also gave a positive reaction with RF applied to the tissue, indicating that the reactant for RF is bound in the tissue.