B Lymphocytes Enhance Interferon- Production by Plasmacytoid Dendritic Cells

Objective. The type I interferon (IFN) system and B cells are activated in many autoimmune diseases, such as systemic lupus erythematosus (SLE). The IFN produced by plasmacytoid dendritic cells (PDCs) stimulates several B cell functions, including autoantibody production. However, not much is known about how B cells influence PDC function. The aim of this study was to investigate the regulatory effect of B cells on IFN production by PDCs. Methods. PDCs and B cells isolated from peripheral blood mononuclear cells from healthy blood donors were stimulated with RNA-containing immune complexes (ICs) consisting of U1 small nuclear RNP and SLE IgG, herpes simplex virus, or oligonucleotide (ODN) 2216, alone or in cocultures. IFN, several other cytokines, and PDC- or B cell–associated surface molecules were analyzed using immunoassays or flow cytometry. Results. B cells enhanced IFN production by PDCs up to 47-fold, and the effect was most pronounced for PDCs stimulated with RNA-containing ICs. AntiCD31 antibody reduced RNA-containing IC–induced IFN production by 80% but had no effect on IFN production when ODN 2216 was used as an inducer. Supernatants from ODN 2216–stimulated B cells promoted IFN production by PDCs, while supernatants from RNA-containing IC–stimulated B cells did not. Conclusion. Our results showed that a novel function of B cells is enhancement of type I IFN production by PDCs. Because B cells are activated by type I IFN, this PDC–B cell cross-talk might be of fundamental importance in the etiopathogenesis of SLE and contribute to long-term immune activation in SLE and other systemic rheumatic diseases.