Immunofluorescence staining profiles of glomerular diseases: a single-center retrospective study

Immunofluorescence (IF) staining is essential for diagnosing glomerular diseases, yet comprehensive characterization of immune deposition patterns remains limited. We retrospectively analyzed 10,489 consecutive native kidney biopsies (2011–2022) from a tertiary center. IF staining for IgA, IgG, IgM, C1q, C3, C4d, and fibronectin was semi-quantitatively graded (0–4+) and deposits classified as mesangial area only (MAO), glomerular capillary loop only (GCLO), or combined mesangial–capillary loop (MA–GCL). IgA nephropathy (IgAN) was the most frequent diagnosis (38.4 %), followed by membranous nephropathy (16.8 %) and focal segmental glomerulosclerosis (13.7 %). IgA deposition was universal in IgAN and IgA vasculitis nephritis (IgAVN), predominantly mesangial (84 % and 78 %, respectively), with MA–GCL co-deposition in 16–21 % of cases. Co-deposition with IgM (58 %), C3 (67 %), and C4d (15 %) was frequent in IgAN. Correlation analysis revealed significant associations between mesangial IgA intensity and mesangial IgM (ρ = 0.26), C3 (ρ = 0.61), C4d (ρ = 0.31), and glomerular C4d (ρ = 0.35) (all P < 0.05), while IgAVN showed additional correlation with fibronectin (ρ = 0.35). C4d positivity was also observed in hypertensive nephropathy (54.7 %). These findings define disease-specific IF profiles and highlight complement activation and fibronectin deposition as potential contributors to IgA-mediated glomerular injury. Integration of quantitative IF data with clinical outcomes may improve risk stratification and inform complement-targeted therapeutic strategies.