Serum IgG binding to human mesangial cells in patients with lupus nephritis and its correlation with disease activity

Basic/Experimental Immunology 2 (Poster): SA-PO2191BACKGROUND: Mesangial immunoglobulin deposition is a hallmark in lupus nephritis. We previously demonstrated that human anti-dsDNA antibodies could bind to human mesangial cells (HMC). In this study we investigated the binding activity of serum IgG to HMC and its correlation with clinical parameters in lupus patients. METHODS: Serial serum samples were obtained from 23 patients with biopsy-proven diffuse proliferative lupus nephritis over a mean follow-up of 74 months. Binding activity (expressed as OD) of total serum IgG and its subclasses (IgG1, IgG2, IgG3, IgG4) to HMC was measured using a cellular ELISA and its correlation with clinical or laboratory parameters investigated. Sera from 23 healthy individuals were used as controls. RESULTS: A total of 189 samples were collected - 48 samples during active and 141 during inactive disease, defined according to clinical assessment. Binding of serum total IgG to HMC was 0.12±0.09, 0.59±0.37 and 0.74±0.43 OD for healthy controls, inactive lupus, and active lupus respectively (P=0.023 active vs inactive, P<0.001 controls vs active or inactive disease). Binding of serum IgG1 to HMC was 0.05±0.05, 0.41±0.38 and 0.55±0.40 OD for the three groups respectively (P=0.037 active vs inactive, P<0.001 controls vs active or inactive disease). Controls and lupus patients did not differ in the binding of serum IgG2, IgG3 or IgG4 to HMC. HMC-binding activity of total IgG and IgG1 correlated with anti-dsDNA antibody levels (r=0.26 and 0.39 respectively, P<0.001 for both), and inversely correlated with C3 levels (r=-0.17 and -0.45 respectively, P