Rheumatoid Factors

Rheumatoid factors (RFs) are autoantibodies reacting against the Fc region of immunoglobulin (Ig)G. RFs are the first autoantibodies described in rheumatoid arthritis (RA), although they are also present in several other autoimmune diseases, in infectious conditions, as well as in healthy subjects. They are currently detectable by standardized quantitative assays (enzyme-linked immunosorbant assay, nephelometry), which are more reliable than the original semiquantitative agglutination techniques. Whether RFs display a pathogenic role in RA is still unclear; however, in favor of such a hypothesis are: i) their ability to form immune complexes both locally - in the synovial space - and systemically; ii) their association with aggressive disease characterized by erosive arthritis and extra-articular manifestations; and iii) the decrease in RF titers after successful therapy with disease-modifying antirheumatic drugs and biologic agents. Although a strong effort has been made in the last decade to find new powerful biomarkers particularly for the early stage of RA, RFs are still one of the most reliable diagnostic/prognostic biomarkers for RA.