Positive and negative regulation of the Fcγ receptor–stimulating activity of RNA-containing immune complexes by RNase

U1RNP complex, Ro/SSA and La/SSB are major RNA-containing autoantigens. Immune complexes (ICs) composed of RNA-containing autoantigens and autoantibodies are suspected to be involved in the pathogenesis of some systemic autoimmune diseases. Therefore, RNase treatment, which degrades RNA in ICs, has been tested in clinical trials as a potential therapeutic agent. However, no studies have specifically evaluated the effect of RNase treatment on the Fcγ receptor-stimulatory activity of RNA-containing ICs. In this study, using a reporter system that specifically detects Fcγ receptor-stimulatory capacity, we investigated the effect of RNase treatment on the Fcγ receptor-stimulatory activity of RNA-containing ICs composed of autoantigens and autoantibodies from patients with systemic autoimmune diseases such as systemic lupus erythematosus. We found that RNase enhanced the Fcγ receptor-stimulatory activity of Ro/SSA- and La/SSB-containing ICs, but attenuated that of the U1RNP complex-containing ICs. RNase decreased autoantibody binding to the U1RNP complex, but increased autoantibody binding to Ro/SSA and La/SSB. Our results suggest that RNase enhances Fcγ receptor activation by promoting the formation of ICs containing Ro/SSA or La/SSB. Our study provides new insights into the pathophysiology of autoimmune diseases involving anti-Ro/SSA and anti-La/SSB autoantibodies, and into the therapeutic application of RNase treatment for systemic autoimmune diseases.