Both eosinophil peroxidase (EPO) and neutrophil myeloperoxidase (MPO) preferentially oxidize SCN(-) to generate HOSCN, a weak, sulfhydryl-reactive oxidant, as a major physiologic product. We here show that HOSCN is a uniquely potent phagocyte oxidant inducer of E-selectin, ICAM-1, and VCAM-1 expression in HUVEC as detected by Western blot and flow cytometry. EMSA and inhibitor studies show that HOSCN up-regulation of these adhesion molecules is transcriptionally mediated through a mechanism that is dependent upon activation of the NF-kappaB p65/p50 transcription factor and constitutively suppressed by PI3K-Akt pathway activity. HUVEC monolayers exposed to HOSCN bind 8-fold more neutrophils and 3- to 4-fold more Aml14.3D10 cells (a differentiated cell line model of mature eosinophils) than control monolayers. Blocking Ab studies confirm the involvement of E-selectin and ICAM-1 but not VCAM-1 in neutrophil adhesion and of all three in Aml14.3D10 adhesion. Intraperitoneal injection of HOSCN evoked an 8-fold increase in neutrophil peritoneal extravasation. In addition to NF-kappaB, HOSCN also activates the potentially proinflammatory transcription factors Stat4, CDP, GRE, CBF, Ets-1/PEA3, and TFIID, a pattern easily distinguishable from that induced by LPS. These results suggest that phagocyte peroxidases function to amplify inflammation through a novel, HOSCN-specific oxidant mechanism.