Circulating immune complexes in rheumatoid arthritis with extra-articular manifestations

Circulating immune complexes (CIC) and complement C4, C3 and CH50 levels in serum were monitored during 6-30 months in 10 patients with rheumatoid arthritis and extra-articular manifestations (EM). A total of 58 observations were made, 17 at times when new EM emerged, 41 at times when the patients were in a steady state. CIC were demonstrated by two methods, viz. a complement consumption test (CCT) and a polyethyleneglycol (PEG) precipitation assay. The precipitates were analysed for their content of IgG, IgM and IgA. The CCT titre decreased significantly at the time of a new EM, whereas PEG precipitates were found most often at this time. Two types of precipitate could be demonstrated. One consisted of IgG only, which was found most often when the patients were in a steady state. The other one was composed of IgG and other immunoglobulins, most often IgA. The latter type was found most often at the time when the patients developed new EM. Subnormal serum complement levels were demonstrated frequently. The level of C4 was significantly lower at the time of a new EM, compared with the level of patients with RA but without EM. The decrease in anticomplementary effect and the signs of complement activation suggest that the qualitative and quantitative changes in CIC observed at the time of new EM were the cause rather than the consequence of the clinical manifestations.