The pathogenetic role of immunoglobulin G from patients with systemic lupus erythematosus in the development of lupus pleuritis

Abstract

Objective. To investigate the pathophysiological effect of immunoglobulin G (IgG) from systemic lupus erythematosus (SLE) patients on pleural mesothelial cells and related mechanisms. Methods. Serum IgG from 28 lupus patients and 13 healthy controls was purified by protein-G affinity chromatography. The concentrations of anti-dsDNA-, anti-histone- and/or anti-nucleohistone-containing IgGs were determined by enzyme-linked immunosorbent assay (ELISA). Lupus patients were divided into an active (n=12) and an inactive group (n=16) on the basis of the SLE Disease Activity Index (SLEDAI). The binding of IgG to a human pleural mesothelial cell line (MeT-5A) under different conditions, including pretreatment with DNase and preincubation with exogenous histone, DNA or nucleohistone, was examined using flow cytometry and cellular ELISA. The effect of IgG on MeT-5A cell proliferation was studied using an MTT assay. Gene expression and protein synthesis for interleukin 1β (IL-1β), monocyte chemoattractant protein 1 (MCP-1) and transforming growth factor β1 (TGF-β1) in MeT-5A cells were determined using reverse transcription-polymerase chain reaction and ELISA. Results. The binding of IgG to MeT-5A cells was higher in the active lupus group than the inactive lupus group (P=0.047) and controls (P=0.003). The binding decreased in both lupus groups following pretreatment of MeT-5A cells with DNase. The binding of IgG to MeT-5A cells was greater by 112% in the active lupus group after preincubation with histone (P < 0.001), but not with DNA or nucleohistone. Exposure of MeT-5A cells to IgG from either lupus group induced cell proliferation when compared with IgG from healthy controls (P=0.04). Gene expression and protein synthesis of MCP-1, TGF-β1 and IL-1β in MeT-5A cells were significantly increased after incubation with IgG from patients with active lupus when compared with IgG from the inactive lupus and control groups (P<0.01). The concentration of anti-dsDNA antibodies correlated with the binding of IgG to MeT-5A cells and the synthesis of cytokines by MeT-5A cells. The serum level of anti-histone antibodies in the active lupus group was higher than that in the inactive group (P=0.015) and the serum concentration correlated with cell binding and MCP-1 production. Conclusions. IgG from lupus patients can bind to MeT-5A cells and the binding is modulated by DNA or histone. Binding of anti-dsDNA-containing IgG to MeT-5A cells induces the synthesis of proinflammatory cytokines. Our findings suggest that the binding of anti-dsDNA antibodies, particularly the IgG isotype, to pleural mesothetium plays a direct pathogenetic role in inducing inflammatory injury in the serositis of SLE. © British Society for Rheumatology 2003; all rights reserved.