Circulating IgG4 Anti-IgG Antibodies in Patients with Idiopathic Membranous Nephropathy

Abstract

IgG4 is the predominant subclass of glomerular IgG in idiopathic membranous nephropathy (MN) . To investigate the role of IgG4 in MN we measured the levels of serum IgG4 anti-IgG antibodies in patients with various glomerular diseases.
The level of serum IgG4 anti-IgG antibodies (U / ml) was assessed by solid-phase enzyme-linked immunosorbent assay (ELISA) in serum samples from patients with various glomerular diseases; MN (n = 27), IgA nephropathy (IgAN) (n =15), lupus nephritis (LN) (n =15), and minimal change nephrotic syndrome (MCNS) (n =15) . Thirteen normal human serum (NHS) samples were obtained from healthy volunteers (HVs) . In addition, the serum IgG4 level (mg/ml) was determined by subclass specific ELISA in the same samples. IgG4 anti-IgG 1 antibodies were elevated in MN patients. However, there was no significant difference in this level between MN and the other disease groups. In all groups of patients, the levels of the serum IgG4 anti-IgG 1 antibodies increased with serum IgG4 concentration. Only the slope of the regression line for MN patients was higher than those for the other groups (MN, 42.241; IgAN, 11.148; LN, 19.795; MCNS, 18.326; HVs, 21.244) . When the serum IgG4 anti-IgG 1 index [IgG4 anti-IgG 1 antibodies (U / ml) / IgG4 (mg/ml) ] in patients with MN, IgAN, LN or MCNS was compared with NHS, the index increased significantly only in patients with MN (MN = 38.6 ± 20.5 (mean ± SD) (P<0.01 vs NHS) ; IgAN =17.1 ± 11.7; LN = 22.2 ± 14.1; MCNS = 23.7 ± 13.9, and NHS = 23.6 ± 10.6. Our results suggest that IgG4 anti-IgG antibodies (particularly IgG4 anti-IgG 1 antibodies) may be involved in immune-deposit formation in MN.