Serine protease inhibitor-6 inhibits granzyme B-mediated injury of renal tubular cells and promotes renal allograft survival.

Background: Protease inhibitor 9 (PI-9) is an intracellular serpin that specifically inhibits granzyme B, a cytotoxic serine protease found in the cytosolic granules of cytotoxic T lymphocytes and natural killer cells. Enhanced cortical expression of PI-9 has been observed in kidney allografts with subclinical rejection, suggesting that the tubular epithelial cell (TEC) expression of this protein may have a protective role and attenuate overt allograft rejection.

Methods And Results: We demonstrate that TEC express SPI-6 protein, the murine homolog of PI-9, basally with a modest increase after cytokine exposure.