Autoantibodies, immunoglobulins and Gm allotypes in nodal generalized osteoarthritis.

The frequencies of autoantibodies, including class specific rheumatoid factors, Gm allotypes, and levels of immunoglobulins were determined in 86 patients with nodal generalized osteoarthritis (NGOA), 79 patients with non-nodal large joint osteoarthritis (LJOA), and 90 non-osteoarthritic controls. NGOA patients had a higher frequency of IgG rheumatoid factor (P less than 0.0001) compared to LJOA and normal subjects. Both osteoarthritic groups had lower mean levels of IgA than normals (P less than 0.05), and NGOA patients had a higher frequency of subnormal IgA levels than normals. No differences in other rheumatoid factors nor in frequencies of Gm allotypes were seen. These data support characterization of NGOA as a distinct subset of osteoarthritis, and suggest involvement of immune processes in its pathogenesis.