TSP-4 (P387)–mediated H₂O₂ release from PMNs depends on activation of p38 MAPK downstream of engagement of α_Mβ₂. PMA-stimulated PMNs were preincubated with specific inhibitors of p38 MAPK (SB202190), ERK 1/2 (PD98059), and protein kinase A (PKA; KT5720) for 30 minutes at RT. Subsequently, the cells were seeded onto (P387) TSP-4–coated plates. Adherent cells were (A) lysed and analyzed on Western blots with Abs to phospho- and total p38 MAPK or (B) measured for H₂O₂ release as described. (C-D) PMA-stimulated PMNs were pretreated with the (Fab)₂ fragments of function-blocking mAbs to various integrins (20 μg/mL), the α_Mβ₂ ligand NIF (10 nM) or RGD peptide (50 μM) for 20 minutes at 37°C. The cells were allowed to adhere to (P387) TSP-4 and p38 MAPK phosphorylation (C), and H₂O₂ levels (D) were assayed as described. The results are means ± SEMs of quadruplet measurements from 3 blood donors.