Expression of transforming growth factor-β isoforms in human glomerular diseases. Protein and mRNA expression of TGF-β isoforms, TGF-β1, -β2 and -β3, and deposition of fibronectin containing extra domain A (fibronectin EDA+) and plasminogen activator inhibitor-1 (PAI-1) were studied in human chronic glomerulonephritis and diabetic nephropathy. Normal kidneys showed similar, weak immunostaining for all three TGF-β isoforms. TGF-β mRNA expression was weak for all isoforms with TGF-β1 > TGF-β3>> TGF-β2. In thin basement membrane disease and minimal change disease, disorders where extracellular matrix accumulation is not a feature, immunoreactivity and mRNA expression did not differ from normal. In contrast, diseases characterized by extracellular matrix accumulation (IgA nephropathy, focal and segmental glomerulosclerosis, crescentic glomerulonephritis, lupus nephritis and diabetic nephropathy) all showed significantly increased expression of the three TGF-β isoforms in glomeruli and the tubulointerstitium. While glomerular and tubulointerstitial deposition of two matrix components induced by TGF-β, fibronectin EDA+ and PAI-1, was significantly elevated in all diseases with matrix accumulation, correlation analysis revealed a close relationship primarily with TGF-β1. We conclude that, for a spectrum of human glomerular disorders, increased protein expression of all three TGF-β isoforms and proteins induced by TGF-β is associated with pathological accumulation of extracellular matrix.