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.