Platelets support pulmonary recruitment of neutrophils in abdominal sepsis.

OBJECTIVE: Recent findings indicate that platelets not only regulate thrombosis and hemostasis but may also be involved in proinflammatory activities. Herein, we hypothesized that platelets may play a role in sepsis by activating and priming circulating neutrophils for subsequent recruitment into the lung.
DESIGN: Prospective experimental study.
SETTING: University Hospital Research Unit. SUBJECT: Male C57BL/6 mice.
INTERVENTIONS: Lung edema, bronchoalveolar infiltration of neutrophils, levels of myeloperoxidase, expression and function of membrane-activated complex-1 (Mac-1) on neutrophils and the CXC chemokines, macrophage inflammatory protein-2, and cytokine-induced neutrophil chemoattractant were determined after cecal ligation and puncture (CLP). Mice received a platelet-depleting antibody as well as antibodies directed against P-selectin glycoprotein-ligand-1 and Mac-1 before CLP induction.
MEASUREMENTS AND MAIN RESULTS: CLP caused significant pulmonary damage characterized by neutrophil infiltration, increased levels of CXC chemokines, and edema formation in the lung. Furthermore, CLP up-regulated Mac-1 expression on neutrophils and increased the number of neutrophils binding platelets in the circulation. Interestingly, depletion of platelets reduced CLP-induced edema and neutrophil recruitment in the bronchoalveolar space by >60%. Furthermore, depletion of platelets reduced Mac-1 expression on neutrophils. On the other hand, inhibition of P-selectin glycoprotein-ligand-1 abolished CLP-induced neutrophil-platelet aggregation but had no effect on neutrophil expression of Mac-1.
CONCLUSIONS: These data demonstrate that platelets play a key role in regulating infiltration of neutrophils and edema formation in the lung via upregulation of Mac-1 in abdominal sepsis.