Inhibition of Fc-rosette formation by synovial fluids from patients with rheumatoid arthritis.

Human red cells sensitized with one of the Rh antisera (Ripley) form rosettes (Fc-rosette) with human B lymphocytes and the rosettes are well inhibited by aggregated human IgG. As synovial fluids from patients with rheumatoid arthritis are usually hypocomplementaemic and frequently contain immune complexes, they were used for the inhibition of Fc-rosette formations in this study. The Fc-rosette inhibitory rates were inversely correlated with the levels of CH50 and C4 in the synovial fluids. Fractionation studies of the synovial fluids by ultracentrifugation and Sephadex G200 gel filtration indicated that main inhibitory activities were present in macromolecular fractions. Reduction and alkylation of the synovial fluids resulted in marked reductions of inhibitory activities. The tested synovial fluids did not contain anti-HLA activity as assessed by the microcytotoxicity test. The Fc-rosette inhibitory rates were not correlated with the levels of C3 and immunoglobulins, nor with the activity of rheumatoid factors in the synovial fluids. These results indicate that the Fc-rosette formations are inhibited by the immune complexes contained in the synovial fluids and it was confirmed that the Fc-rosette inhibition test is a simple and sensitive method for the detection of circulating immune complexes.