Role of complement system in patients with biopsy-proven immunoglobulin G4–related kidney disease

Summary Hypocomplementemia has been frequently reported in immunoglobulin G4–related kidney disease (IgG4-RKD). However, studies on the role of complement system in IgG4-RKD are lacking. A total of 40 429 renal biopsies from January 2010 to January 2018 were reexamined in the present study, and 17 patients were confirmed to meet the criteria of IgG4-RKD. According to the serum C3 levels, they were divided into 2 groups: the low-C3 group (C3 P  = .025), higher serum IgG4 concentrations ( P  = .003), higher positive rates in rheumatoid factor ( P  = .033), more severe storiform fibrosis ( P  = .007) at diagnosis, and higher blood urea nitrogen levels at the latest test ( P  = .04). The serum levels of C3 were in negative correlation with the serum levels of IgG4 ( P  = .003), the levels of rheumatoid factor ( P  = .002), renal deposition of C1q ( P  = .028), storiform fibrosis ( P P  = .015), the amount of renal IgG4–positive (IgG4 + ) plasma cells ( P  = .020), the ratios of IgG4 + plasma cells/CD138 + cells ( P  = .018), and the blood urea nitrogen concentrations at the last test ( P  = .023). Our study shows that IgG4-RKD is a relatively rare entity. Complement system may participate in the development of IgG4-RKD.