Objective: To investigate the possibility of IgG4/IgG as one of biomarkers to reflect disease activity and the relapse of idiopathic membranous nephropathy (IMN).
Methods: Plasma and urine samples were obtained from patients with IMN (Twenty-four patients had follow-up data), minimal change disease (MCD) and focal segmental glomerulosclerosis (FSGS) before immunosuppressive therapy. Concentrations of plasma and urine IgG4 and total IgG were detected by sandwich ELISA. The ratio of IgG4/IgG was calculated as the concentration of IgG4 divided by total IgG.
Results: Both plasma and urine IgG4/IgG ratios were significantly higher in IMN group compared with MCD or FSGS group (both P<0.05). In IMN, both plasma and urine IgG4/IgG ratios in patients with nephritic syndrome were significantly higher versus those with subnephrotic proteinuria (P=0.063; P<0.05). Both plasma and urine IgG4/IgG ratios were significantly decreased with remission (P<0.05) and maintained or even increased with resistance to therapy. Patients who relapsed within 2 years had higher urine IgG4/IgG-ratios than those who had no relapse (P<0.05), and patients with urine IgG4/IgG-ratios≥9% upon renal biopsy had higher relapse tendency (P=0.071).
Conclusion: Both plasma and urine IgG4/IgG ratios might be a promising biomarker to reflect disease activity of IMN, and higher urine IgG4/IgG ratios might suggest higher relapse tendency.