The clinical and pathogenetic significance of rheumatoid factors.

Rheumatoid factors are immunoglobulins with antibody specificity for antigenic sites on the Fc part of the heavy chain of IgG. The heterogeneity of RF in terms of antigenic specificity and class of immunoglobulin is indicative of the complexity of the provoking immune response. There is little doubt that in many patients rheumatoid factors are autoantibodies which form part of immune complexes, and that complexes containing IgG rheumatoid factor appear to be of pathogenetic importance. Although IgM rheumatoid factors are not specific for RA, their detection aids in the diagnosis and categorisation of rheumatoid arthritis. On the other hand, IgG rheumatoid factors occur in a variety of rheumatic diseases and are of little diagnostic value.