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Rheumatoid arthritis (RA) is a joint disease characterized by inflammation of the joints, stiffness, swelling, overgrowth of cartilage tissue, and pain. It is associated with the production of abnormal immune system factors such as rheumatoid factor, antinuclear antibodies, and circulating immune complexes, as well as altered levels of immunoglobulins (Ig; immune proteins) and complement (proteins that destroy bacteria and other foreign cells). RA may be associated with complications of the kidney, including mesangial nephropathy, disease of the tissue supporting the glomeruli, which filter blood through the kidney; membranous glomerulonephritis, the inflammation of the kidney with the development of membranes; and amyloidosis, the deposition of amyloid, a protein-carbohydrate substance, in the tissue and organs. The levels of various types of Ig, the complement proteins C3 and C4, circulating immune complexes, and antinuclear antibodies, were measured in 56 RA patients with mesangial nephropathy, 13 RA patients with membranous glomerulonephritis, 20 RA patients with amyloidosis, and 35 RA patients without kidney disease. IgA and IgM levels were higher in patients with mesangial nephropathy and amyloidosis than in RA patients without kidney disease. IgA levels were higher in patients with IgA deposits than those without IgA deposits, and highest in patients with IgA glomerulonephritis, which occurred in five percent of RA patients. The results show that circulating immune complexes do not have a major role in kidney disorders associated with RA. (Consumer Summary produced by Reliance Medical Information, Inc.)