Circulating Immune Complexes in Mixed Connective Tissue Disease

Abstract

Circulating immune complexes were measured by three assays (monoclonal rheumatoid factor radioimmunoassay, Clq‐binding assay, Raji cell radioassay) in sera from patients with mixed connective tissue disease. Evidence for circulating immune complexes was found by at least one method in 94% of sera. The highest frequency of positive results was noted by the Raji cell radioassay (88%). However, a significant number of patients also had immune complexes measured by the Clq‐binding assay (50%) and monoclonal rheumatoid factor radioimmunoassay (45%). Further, the levels of immune complexes as measured by the Raji cell radioassay, and to a lesser extent the Clq‐binding assay, correlated with disease activity and represent a potentially useful clinical tool. The pattern of reactivity in mixed connective tissue disease sera differed from rheumatoid arthritis, scleroderma, and polymyositis. This suggests that a spectrum of immune complexes is found in these rheumatic diseases and supports the concept that mixed connective tissue disease is distinct from these diseases.