In Vitro Cytotoxicity of Human Lymphocytes for Sensitized Chicken Erythrocytes Is Inhibited by Sera from Rheumatoid Arthritis Patients

Sera containing rheumatoid factors inhibited the in vitro cytotoxicity of human peripheral lymphocytes for sensitized chicken erythrocytes. In contrast, sera from healthy blood donors did not inhibit the reaction. The inhibitory activity of rheumatoid factor sera was enhanced in the presence of heataggregated human gamma globulin (HGG). Aggregated HGG per se or added to blood donor sera was only slightly inhibitory in this system. Lymphocyte cytotoxicity induced by phytohaemagglutinin was not inhibited by any of these sera, not even in the presence of aggregated HGG. It is concluded that a majority of sera containing rheumatoid factors also contain factors inhibitory to the in vitro cytotoxicity of human lymphocytes for sensitized target cells. The strong inhibitory activity of mixtures of rheumatoid factor sera and aggregated HGG in the sensitized target cell system may be due to complex formation between anti‐immunoglobulin factors and gamma globulin. Such complexes might inhibit the reaction by binding to the surface of lymphocytes cytotoxic for target cells carrying antigen‐antibody complexes.