Inhibition of alveolar neutrophil immigration in endotoxemia is macrophageinflammatory protein 2 independent

Background. Altered transendothelial migration and delayed apoptosis of neu trophils (PMN) have been implicated as contributing to infection in patient s with gram-negative sepsis. Macrophage inflammatory protein 2 (MIP-2) sign als PMN immigration and may alter other PMN functions. We tested the hypoth esis that sequential endotoxin challenge in vivo alters PMN apoptosis and c hemotactic responses. Materials and methods. Endotoxemia was induced in male Wistar rats (250 g) via intraperitoneal (TP) administration of LPS (4 mg/kg). After 18 h, intra tracheal (IT) injection of LPS (400 mu g/kg) was performed. Control animals received saline injections. Four hours after IT-LPS, circulating and bronc hoalveolar lavage (BAL) PMN were isolated. PMN yields were calculated, and apoptosis was quantified after 18 h in culture by annexin V-fluorescein iso thiocyanate FACS analysis. BAL MIP-2 concentrations were determined by ELIS A. PMN chemotaxis to MIP-2 and IL-8 was determined using a fluorescent in v itro migration assay. Results. Endotoxemia (IP-LPS) significantly decreases BAL PMN yield in resp onse to an in vivo IT-LPS challenge. TT-LPS inhibits BAL PMN apoptosis to t he same extent as sequential IP/IT-LPS. Alveolar MIP-2 concentrations are s imilar in the two groups. In vitro migration to IL-8 and MIP-2 was inhibite d in PMN from endotoxemic versus control animals. Conclusions. These data demonstrate that endotoxemia inhibits PMN migration . despite similar MIP-2 concentrations in the alveolus. Sequential insults do not affect the inhibition of apoptosis. In vitro, PMN from endotoxemic a nimals display impaired chemotaxis to MIP-2 and interleukin-8. This may res ult in an inadequate host defense that contributes to increased ICU-acquire d pneumonia in septic patients. (C) 2000 Academic Press.