Neutrophils (polymorphonuclear neutrophils; PMN) and a redundant system of chemotactic cytokines (chemokines) have been implicated in the pathogenesis of the acute respiratory distress syndrome in patients with sepsis. PMN express two cell surface receptors for the CXC chemokines, CXCR1 and CXCR2. We investigated the expression and function of these receptors in patients with severe sepsis. Compared with normal donors, CXCR2 surface expression was down-regulated by 50% on PMN from septic patients (p< 0.005), while CXCR1 expression persisted. In vitro migratory responses to the CXCR1 ligand, IL-8, were similar in PMN from septic patients and normal donors. By contrast, the migratory response to the CXCR2 ligands, epithelial cell-derived neutrophil activator (ENA-78) and the growth-related oncogene proteins, was markedly suppressed in PMN from septic patients (p< 0.05). Ab specific for CXCR1 blocked in vitro migration of PMN from septic patients to IL-8 (p< 0.05), but not to FMLP. Thus, functionally significant down-regulation of CXCR2 occurs on PMN in septic patients. We conclude that in a complex milieu of multiple CXC chemokines, CXCR1 functions as the single dominant CXC chemokine receptor in patients with sepsis. These observations offer a potential strategy for attenuating adverse inflammation in sepsis while preserving host defenses mediated by bacteria-derived peptides such as FMLP.