Intraglomerular distribution of fibronectin in primary glomerular diseases

The intraglomerular distribution of fibronectin was examined in 152 renal biopsy specimens with the direct immunofluorescence technique. Fibronectin was detected only in the mesangial area in normal glomeruli, while in proliferative glomerulonephritis, it extended from the mesangium to the pericapillary regions proportionately with the proliferative changes. In membranoproliferative glomerulonephritis, fibronectin globally extended in the glomeruli. Also in membranous nephropathy, fibronectin was observed in the capillary walls despite an absence of proliferation. Electron microscopic examinations revealed that the glomeruli with the pericapillary distribution of fibronectin were mostly found in stage II or III, as determined by WHO criteria. The double immunofluorescence technique demonstrated that in membranous nephropathy fibronectin was on the inner side of the glomerular basement membrane, and that in membranoproliferative glomerulonephritis fibronectin extended concomitantly with the expansion of mesangial matrix. These findings suggest that intraglomerular fibronectin is localized only in the mesangial area in normal glomeruli, and that the pericapillary distribution of fibronectin occurs not only by mesangial proliferation but also by additional unknown mechanisms.