High Serum Beta‐2‐Microglobulin Levels and Circulating Immune Complexes Containing βm AND Anti‐βm Antibodies in Felty's Syndrome

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Abstract
Serum beta‐2‐microglobulin (β2m) levels, incidence and levels of anti‐β2m autoantibodies, and quantity of circulating macromolecular complexes containing β2m were studied in patients with Felty's syndrome (FS), joint‐restricted rheumatoid arthritis (RA), and healthy controls. The serum β2m concentrations detected in the FS group (6.95 ± 2.9 mg/liter) greatly exceeded those of the RA group (3.4 ± 1.2 mg/liter) and the control group (1.42 ± 0.69 mg/liter). Autoantibodies to β2m were frequent in the FS group. Circulating complexes containing β2m, prepared by precipitation in 3% polyethylene glycol, were detected in 65% of FS and 35% of RA patients. In the majority of these cases the solid‐phase Clq purified immune complexes also contained βm. Detection of anti‐β2m antibodies in a significant part of complexes containing β2m suggests the presence of specific immune complexes in this fraction of FS and RA patients.