Detection and partial characterization of immune complexes in patients with rheumatoid arthritis plus Sjogren's syndrome and with Sjogren's syndrome alone

In order to characterize the immune complexes detected in patients with Sjogren's syndrome (SS) and with rheumatoid arthritis (RA), the sera of 19 patients with SS alone and 11 with SS plus RA were examined. Elevated quantities of circulating immune complexes (CIC) were detected in 67% by the C1q-binding assay (C1q-BA), 73% by the C1q-solid phase (C1q-SP) assay, 43% by the monoclonal rheumatoid factor solid phase assay (mRF-SP) and 33% by the mRF-inhibition assay (MRF-Inh). Elevated concentrations of IgM RF were detected in 83% and of IgG RF in 73% of the sera by radioimmunoassay. Strong correlations existed between RF of the IgM and IgG classes and both the C1q-BA and the C1q-SP. Three lines of evidence indicated that RF were important components of the immune complexes detected by these radioimmunoassays. These results indicated that in those patients with RA plus SS, as well as those with SS alone, both IgM and IgG RF made substantial contributions to immune complexes detected both by the C1q-BA and the C1q-SP.