Rheumatoid factors bind beta 2 microglobulin. Detection of beta 2 microglobulin-complexes in rheumatoid arthritis

beta 2 Microglobulin binding rheumatoid factors and occurrence of complexed form of beta 2 microglobulin were found in rheumatoid arthritis (RA) by radioimmunological methods. 1. As related to the appropriate values of control sera and osteoarthritic synovial fluids, one of the six sera and five of the six synovial fluids of RA patients exhibited increased binding activity for 125I-beta 2 microglobulin, 2. Rheumatoid factors (RF) purified by means of immunoadsorbent bound beta 2 microglobulin; 3. Both 19S and 7S components of sera, synovial fluids and purified RF samples had beta 2 microglobulin binding activity, which was inhibited by an excess of unlabeled beta 2 microglobulin; 4. Complexed (3% PEG 6000 insoluble) beta 2 microglobulin was found in three of fourteen sera and in twelve of fourteen synovial fluids of RA patients. Level of complexed beta 2 microglobulin was independent of its total concentration in the original samples; 5. In the fraction of synovial fluids enriched immune complex the amount of beta 2 microglobulin was in positive correlation with quantity of RF. Presumable immunological and pathological significance of "anti-beta 2 microglobulin"-like cross-reactive RF antibodies is discussed.