Immune complexes from SLE sera induce IL10 production from normal peripheral blood mononuclear cells by an FcγRII dependent mechanism: implications for a possible vicious cycle maintaining B cell hyperactivity in SLE

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Abstract
Background: Raised interleukin (IL)6 and IL10 levels are thought to contribute to the pathogenesis of systemic lupus erythematosus (SLE) by enhancing autoantibody production and immune complex (IC) formation. These immune complexes can then stimulate cellular reactions through Fc and complement receptors. Objective: To investigate whether circulating SLE ICs stimulate type 2 cytokine production. Methods: Twenty serum samples from patients with active SLE were compared with sera from 18 healthy controls. Sera and polyethylene glycol (PEG) precipitates from sera were added to peripheral blood mononuclear cell (PBMC) cultures, and the production of IL10 and IL6 was investigated by enzyme linked immunospot assay (ELISPOT) and enzyme linked immunosorbent assay (ELISA). Fc gamma receptor (FcγR) antibodies were used in blocking experiments, and flow cytometry was used to assess the correlation between monocyte FcγR expression and IC-induced cytokine production. Results: Ten per cent dilutions of the SLE sera induced a significantly increased number of IL10-producing cells in comparison with control sera (median, 11.75 v 1.25 spot forming cells/50 000 PBMC; pConclusions: SLE sera stimulate IL10 and IL6 production from PBMC, and this effect is at least partly explained by precipitable ICs acting through FcγRII. This effect provides a possible mechanism for the enhanced production of IL10 in SLE, whereby B cell activation, antibody production, IC stimulated monocytes/macrophages, and type 2 cytokines create a vicious cycle that may help to maintain B cell hyperactivity in SLE.

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