The pathogenetic role of immunoglobulin G from patients with systemic lupus erythematosus in the development of lupus pleuritis.
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 1beta (IL-1beta), monocyte chemoattractant protein 1 (MCP-1) and transforming growth factor beta1 (TGF-beta1) 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-beta1 and IL-1beta 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 mesothelium plays a direct pathogenetic role in inducing inflammatory injury in the serositis of SLE.
Guo
H
H
Department of Medicine, University of Hong Kong, Queen Mary Hospital, 102 Pokfulam Road, Hong Kong.
Leung
J C K
JC
Chan
L Y Y
LY
Chan
T M
TM
Lai
K N
KN
D000208:Acute Disease; D000328:Adult; D000974:Antibodies, Antinuclear / Q000097:blood; D001323:Autoantibodies / Q000097:blood; D016022:Case-Control Studies; D002455:Cell Division; D002908:Chronic Disease; D016207:Cytokines / Q000096:biosynthesis / Q000235:genetics; D004847:Epithelial Cells / Q000276:immunology; D005260:Female; D005434:Flow Cytometry; D015870:Gene Expression; D006657:Histones / Q000276:immunology; D006801:Humans; D007074:Immunoglobulin G / Q000032:analysis / Q000276:immunology* / Q000494:pharmacology; D008180:Lupus Erythematosus, Systemic / Q000276:immunology*; D008297:Male; D010994:Pleura / Q000276:immunology; D010995:Pleural Diseases / Q000276:immunology*
D000974:Antibodies, Antinuclear; D001323:Autoantibodies; D016207:Cytokines; D006657:Histones; D007074:Immunoglobulin G