Polyclonal human antibodies to IgG (rheumatoid factors) which cross-react with cell nuclei

Antibodies to human IgG (rheumatoid factors (RF) from serum Han resembled the 'intermediate' complexes of sera from some patients with rheumatoid arthritis. These RF were isolated from heat-inactivated serum by affinity chromatography on agarose-coupled human IgG. Indirect immunofluorescence revealed that the isolated RF cross-reacted with cell nuclei from many species. Virtually all the antinuclear factor (ANF) activity of this serum was extracted by IgG-agarose. Alternative explanations of this phenomenon, such as nonspecific binding of a separate population of ANF, binding of ANF to the immunosorbent via an IgG RF-IgG ANF immune complex, or presence of nuclear antigens on the immunosorbent, were ruled out. The cross-reacting antibodies possessed both kappa and lambda light chains and predominantly gamma and some mu heavy chains, indicating that they were of polyclonal origin. The antinuclear activity was present in the F(ab')2 fragments. The interpretation of this strange cross-reaction is briefly discussed.