[A solid-phase ELISA with specificity for rheumatoid factors of classes IgA, IgG and IgM]

A solid phase ELISA was developed for the simple and rapid determination of rheumatoid factors (RF) of all major immunoglobulin classes. Micro-ELISA-plates were coated with human Fc-fragments and incubated with various dilutions of serum samples as well as with an international RF reference serum. Rheumatoid factors were quantitatively detected by rabbit antibodies (RaHIgA(alpha), RaHIgM(mu), RaHIgG(Fab] conjugated with alkaline phosphatase. The specificity of the ELISA was proved by means of binding inhibition of all rheumatoid factor classes by heat aggregated human IgG. A comparison of the IgM-RF titres of the latex fixation test with the IgM-RF concentration values of the ELISA yielded high correlation (r = .81).