Description
Rheumatoid arthritis (RA) is a chronic inflammatory disease of unknown etiology. Rheumatoid arthritis is a systemic disease characterized by chronic proliferation and inflammation of joint cartilage and supporting structures. RA is mainly defined by clinical criteria, in which systematic pathogenetic studies have been hampered by doubts about the presence of common pathogenetic mechanisms and the relative lack of unique laboratory findings. IgG rheumatoid factor has been reported to be present in sera of patients with rheumatoid arthritis both with and without IgM rheumatoid factor activity. Rheumatoid factors are IgA, IgG and IgM immunoglobulins with antibody activity directed against antigenic sites on the Fc portion of IgG molecules. Because of its pentavalent structure and ability to cross-link immunoglobulin G antigen, IgM Rheumatoid Factor is the main class identified by clinically available diagnostic assays for Rheumatoid Factor detection. Rheumatoid factors may exist as the mu, gamma, alpha, and epsilon isotypes. Rheumatoid factors are found in 1 to 4 % of the general population. They are present in 75% of adult patients with the highest incidence of rheumatoid factors occurring in persons over 65 years of age and nearly all patients with Felty and Sjogren syndrome. The clinical correlation of an elevated rheumatoid factor should be interpreted cautiously. Increased titers may accompany a variety of acute immune responses, particularly viral infections and a number of other diseases (e.g., infectious mononucleosis, tuberculosis, leprosy, various parasitic diseases, liver disease, sarcoidosis, and lymphoproliferative syndromes). The earliest tests and those still most widely used rely on the agglutinating properties of the IgM class of rheumatoid factors. Sensitized sheep red blood cell (Waaler-Rose) and latex agglutination tests have been developed and routinely employed. These assays are most sensitive for the detection of Rheumatoid factor that is of the IgM isotype because of its multivalent structure. These tests provide a dilution which is difficult to standardize and have laborious processing and poor reproducibility. In contrast to these assays modern ELISA tests are characterized by a higher sensitivity and by the possibility to differentiate between IgA, IgG and IgM Rheumatoid Factors