Inhibition of Neutrophil Migration by Hemopexin Leads to IncreasedMortality Due to Sepsis in Mice

RATIONALE: The reduction of neutrophil migration to the bacterial focus is associated with poor outcome in sepsis. OBJECTIVES: The objective of this study was to identify soluble substances in the blood of septic mice that inhibit neutrophil migration during the early phases of sepsis. Results and methods: A pool of serum obtained from mice two hours after the induction of severe sepsis by cecal ligation and puncture inhibited neutrophil migration. Hemopexin was identified by mass spectrometry as the serum component responsible for this effect. In sepsis, the pretreatment of wild type mice with hemopexin inhibited neutrophil migration to the focus of infection and decreased the survival rate from 87.5% to 50.0%. Hemopexin-null mice submitted to severe sepsis present normal neutrophil migration and, as a consequence, presented low bacteremia and an improvement of 40% in survival rate. Moreover, hemopexin inhibited the neutrophil chemotaxis response evoked by C5a or MIP-2 and induced a reduction of CXCR2 and L-selectin as well as the up-regulation of CD11b expression in neutrophil membranes. The inhibitory effect of hemopexin on neutrophil chemotaxis was prevented by serine protease inhibitors or adenosine-5'-triphosphate (ATP). In addition, serum levels of ATP were decreased at the early stages of severe sepsis. CONCLUSION: These data demonstrate for the first time the inhibitory role of hemopexin on neutrophil migration during sepsis and suggest that the therapeutic inhibition of hemopexin or its protease activity could improve neutrophil migration to the focus of infection and survival in sepsis.