A role for P selectin in complement-independent neutrophil-mediated glomerular injury. Neutrophil recruitment and lung injury following complement activation have been demonstrated to be dependent on endothelial expression of P selectin. In anti-glomerular basement membrane antibody-induced glomerulonephritis (anti-GBM GN) in mice, acute glomerular injury results from complement-independent neutrophil accumulation. The signals for neutrophil recruitment in this model are unknown. Expression of P selectin on glomerular endothelium was demonstrated within 30 minutes of administration of anti-GBM antibody to C57/BL10 mice. This was associated with rapid accumulation of neutrophils in glomeruli which peaked at one hour (6.2 ± 0.5 neutrophils per glomerular cross section [neut/gcs], normal 0.34 ± 0.06 neut/gcs, P < 0.01) and significant proteinuria after 16 hours (3.6 ± 0.5 mg/16 hr, control 0.62 ± 0.13 mg/16 hr, P < 0.01). Complement depletion with cobra venom factor, which reduced serum C3 levels to less than 5% of normal, did not alter expression of P selectin, reduce glomerular neutrophil accumulation (6.7 ± 0.8 neut/gcs) or proteinuria (3.7 ± 0.5 mg/16 hr). Platelet depletion also failed to alter glomerular expression of P selectin, neutrophil accumulation or the development of proteinuria. Mice were treated with an affinity purified anti-human P selectin antibody, which cross reacted with mouse P selectin and blocked P selectin-dependent binding of thrombin-activated mouse platelets to HL60 cells and did not bind to mouse neutrophils. Treatment, one hour prior to the administration of anti-GBM antibody, markedly inhibited glomerular neutrophil accumulation (0.94 ± 0.12 neut/gcs) and prevented proteinuria (1.0 ± 0.2 mg/16 hr), and did not alter binding of anti-GBM globulin in the kidney. These data strongly suggest that the rapid up-regulation of P selectin expression in glomeruli following binding of anti-GBM antibody is an essential signal for neutrophil recruitment in this complement independent model of glomerular injury.