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The deregulation of inflammatory response during sepsis seems to reflect the overproduction of mediators, which suppress leukocyte functions. We investigated the intracellular mechanisms underlying the inability of neutrophils from severe septic patients to migrate toward chemoattractants. Patients with sepsis (52) and 15 volunteers were prospectively enrolled. Patients presented increased circulating levels of tumor necrosis factor-alpha, interferon-gamma, interleukin (IL)-8, and IL-10. Patients showed reduced neutrophil chemotaxis to formyl-methionyl-leucyl-phenylalanine (FMLP), leukotriene B4 (LTB4) or IL-8. No difference in the transcription or expression of the IL-8 receptor, CXCR1, was detected in neutrophils from controls and patients. However, septic neutrophils failed to increase tyrosine phosphorylation and actin polymerization in response to IL-8 or LTB4. In contrast, septic neutrophils, similar to controls, showed phagocytic activity that induced actin polymerization and augmented phosphotyrosine content. Treatment of control neutrophils with cytokines and lipopolysaccharide (LPS) to mimic endogenous septic environment inhibited actin polymerization and tyrosine phosphorylation in response to IL-8 or LTB4. High expression of G protein-coupled receptor kinase 2 (GRK2) and GRK5 was detected in septic neutrophils and control cells treated with cytokines plus LPS. Data suggest that endogenous mediators produced during sepsis might continually activate circulating neutrophils, leading to GRK activation, which may induce neutrophil desensitization to chemoattractants.

Sepsis and septic shock continue to be a major cause of morbidity and mortality in critically ill patients. During the onset of sepsis, several inflammatory mediators, including cytokines, chemokines and nitric oxide are released systemically and mediate most of the pathophysiological events present in sepsis and septic shock, such as cardiovascular dysfunction and target-organ lesions. Polymorphonuclear leukocytes are critical effector cells during the inflammatory process and their migration to the infection focus is extremely important for the local control of bacterial growth and consequently for the prevention of bacterial dissemination. In experimental models and in human sepsis a profound failure of neutrophil migration to the infection focus is observed. It seems that the failure of neutrophil migration is dependent on toll-like receptor 4 (TLR4) and mediated by cytokines and chemokines, which induce the production of nitric oxide that inhibits neutrophil adhesion to venular endothelium and also the neutrophil chemotactic ability.