Tubular osteopontin expression in patients with ANCA-associated glomerulonephritis

To elucidate the role of osteopontin (OPN) in monocyte recruitment in crescentic glomerulonephritis, we investigated immunohistochemical localization of OPN in the kidney and its correlation with clinical and histopathologic parameters in biopsy specimens of patients with myeloperoxidase antineutrophil cytoplasmic autoantibody- (MPO-ANCA) associated glomerulonephritis.

Twelve patients with MPO-ANCA-associated glomerulonephritis were enrolled in this study. Clinical parameters such as creatinine clearance and urinary protein excretion of each patient were obtained at the time of biopsy. Paraffin-embedded sections were used for immunohistochemical staining using the LSAB method. Five cortical interstitial fields randomly selected at original magnification x 200 were assessed using a computer-assisted color image analyzer. Tubular OPN expression was assessed as the percentage of positive area in the tubulointerstitium. Double immunofluorescent staining using antibodies against OPN and alpha(v)beta3 was performed.

In all of the cases studied, OPN was occasionally localized within the glomeruli, and expressed slightly in proximal tubular epithelium and significantly in distal tubular epithelium. Tubular OPN expression tended to be promoted in the interstitium infiltrating by numerous monocytes/macrophages. The extent of tubular OPN expression was positively correlated with serum ANCA titers and urinary OPN concentrations. Enhanced alpha(v)beta3 expression appeared in the distal tubular epithelium expressing OPN.

These results suggest that inducible expression of OPN and alpha(v)beta3 in the tubular epithelium seems to be associated with interstitial moncyte infiltration and subsequent tubulointerstitial changes in human MPO-ANCA-associated glomerulonephritis.