Toll-like receptor 9 activation in neutrophils impairs chemotaxis and reduces sepsis outcome.

OBJECTIVES: To investigate the role of toll-like receptor 9 on sepsis-induced failure of neutrophil recruitment to the site of infection.
DESIGN: Prospective experimental study.
SETTING: University research laboratory.
INTERVENTIONS: Model of polymicrobial sepsis induced by cecal ligation and puncture in wild-type and toll-like receptor 9-deficient mice.
MEASUREMENTS AND MAIN RESULTS: Toll-like receptor 9-deficient mice with cecal ligation and puncture-induced severe sepsis did not demonstrate failure of neutrophil migration and consequently had a low systemic inflammatory response and a high survival rate. Upon investigating the mechanism by which toll-like receptor 9 deficiency prevents the failure of neutrophil migration, it was found that neutrophils derived from toll-like receptor 9--deficient mice with cecal ligation and puncture-induced severe sepsis expressed high levels of chemokine C-X-C motif receptor 2 (CXCR2) and had reduced induction of G-protein-coupled receptor kinase 2.
CONCLUSIONS: These findings suggest that the poor outcome of severe sepsis is associated with toll-like receptor 9 activation in neutrophils, which triggers G-protein-coupled receptor kinase 2 expression and CXCR2 downregulation. These events account for the reduction of neutrophil migration to the site of infection, with consequent spreading of the infection, onset of the systemic inflammatory response, and a decrease in survival.