Anti-immunoglobulin antibodies IV. Cross-reaction of anti-idiotypic antibodies specific for rabbit and murine anti-a1 allotype antibodies with Fc fragment of human immunoglobulins

Anti-idiotype (Id) antibodies against anti-a₁ rabbit allotype antibodies were produced in rabbits and mice by immunization with polyclonal rabbit anti-a₁ allotype or with a monoclonal murine anti-a₁ allotype antibody, respectively. These antibodies recognize an interspecies cross-reactive idiotope on anti-a₁ allotype antibodies. However, these anti-Id antibodies also react with various subclasses of human IgG. In multiple systems, it was shown that these anti-Id antibodies interact with the Fc fragment of human IgG and, therefore, exhibit a rheumatoid factor-like activity. These results support the hypothesis that γ-globulin may not be the only stimulus to clones producing rheumatoid factors and that perhaps other antibodies, especially anti-Id antibodies, also bind γ-globulin secondarily.