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New roles for rheumatoid factor.

In the 1940s, anti-IgG autoantibodies were discovered in the sera of patients with rheumatoid arthritis and given the term rheumatoid factors (RF).' The measurement of agglutinating IgM-RF is still the most useful serological test for the diagnosis ofrheumatoid arthritis. High titers ofIgM-RF are also present in primary Sjogren's syndrome, mixed cryoglobulinemia, and in several different chronic infections (1). Recent advances in molecular and cellularimmunology are gradually revealing the genetic and environmental factors that control RF production. Two sets of results were largely unexpected. First, genes encoding RF are present in most normal people, and their expression is carefully regulated during the development of the immune system. Second, lymphocytes with RF receptors on their plasma membranes are remarkably abundant in normal people, who have only low levels ofcirculating autoantibody. These data have suggested a new role for RF in the capture, processing, and presentation to T cells of antigens trapped in immune complexes. They may explain why RF production is vestained in patients with both rheumatoid arthritis and lymphoproliferative diseases.