Association of serum levels of fibrosis-related biomarkers with disease activity in patients with IgG4-related disease.

Background: The aim of this study was to identify fibrosis-related serological surrogate outcome measures in patients with immunoglobulin G4-related disease (IgG4-RD).
Methods: This was a clinical observational study of 72 patients with untreated IgG4-RD from four institutions in Japan. The serum concentrations of growth differentiation factor 15 (GDF-15), CCL2, hyaluronic acid (HA), amino-terminal propeptide of type III procollagen (PIIINP), and tissue inhibitor of metalloproteinases 1 (TIMP-1) were measured by enzyme-linked immunosorbent assays. The enhanced liver fibrosis (ELF) score was calculated from the TIMP-1, PIIINP, and HA values. We evaluated associations between the values of these biomarkers and laboratory data, the IgG4-RD responder index (IgG4-RD RI) score, and organ involvements.
Results: Compared with the 44 healthy controls, the patients with IgG4-RD showed significantly elevated serum concentrations of GDF-15, MCP-1, HA, PIIINP, and TIMP-1 and ELF scores. The patients' serum concentrations of GDF-15, CCL2, HA, and TIMP-1 (but not PIIINP) were positively correlated with each other. Among them, serum GDF-15 most efficiently distinguished patients with IgG4-RD from healthy controls. Serum GDF-15 was not associated with the IgG4-RD RI score or the number of organ involvements but was independently associated with the presence of retroperitoneal fibrosis and with parotid gland involvement.
Conclusions: We observed increased serological surrogate outcome measures of fibrosis in IgG4-RD. GDF-15 may precisely reflect the fibrotic degree in patients with IgG4-RD.