[Clinical Significance of IgG4 Level in Predicting the Activity and Outcome of Phospholipase A2 Receptor-associated Membranous Nephropathy]

Objective To investigate the feasibility of IgG4 as a biomarker of the activity and outcome of phospholipase A2 receptor (PLA2R)-associated membranous nephropathy (PLA2R-MN). Methods Serum and urine samples were collected from 56 patients with PLA2R-MN,13 patients with secondary membranous nephropathy (SMN),and 10 patients with primary IgA nephropathy (IgAN) when kidney biopsy was performed in the Department of Nephrology,Hangzhou Hospital of Traditional Chinese Medicine from April 2017 to January 2018.Sandwich enzyme-linked immunosorbent assay was employed to measure the serum and urinary IgG4 levels. Results The PLA2R-MN group had higher median serum IgG4/IgG ratio than the SMN group (P=0.009) and the IgAN group (P<0.001) and higher median urinary IgG4/creatinine ratio than the SMN group (P=0.008).In the patients with PLA2R-MN,the median serum IgG4/IgG ratio and urinary IgG4/creatinine ratio were significantly higher in the renal insufficiency group than in the normal renal function group (P=0.049,P=0.015).Moreover,the median serum IgG4/IgG ratio was higher in those with a serum albumin level<30 g/L than in those with a serum albumin level ≥30 g/L (P=0.005).Fifty-three patients with PLA2R-MN were followed up for at least 1 year,and the serum IgG4/IgG ratios of the patients in remission were lower than those of the patients without remission (P=0.005).The median serum IgG4/IgG ratio of 23 patients in remission decreased from 5.82% (4.54%,10.20%)(at initial enrollment) to 2.91% (2.11%,5.37%)(after 1-year follow up) in remission patients (P<0.001).The receiver operating characteristic curve showed that the patients with a serum IgG4/IgG ratio<10.24% had a higher possibility of remission (P=0.005). Conclusion Serum and urinary IgG4 levels may be an indicator of the activity in PLA2R-MN patients and thus may be a predictive biomarker of the outcomes.