The Journal of immunology : official journal of the American Association of Immunologists
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Activated neutrophils contribute to the development and severity of acute lung injury (ALI). Phosphoinositide 3-kinases (PI3-K) and the downstream serine/threonine kinase Akt/protein kinase B have a central role in modulating neutrophil function, including respiratory burst, chemotaxis, and apoptosis. In the present study, we found that exposure of neutrophils to endotoxin resulted in phosphorylation of Akt, activation of NF-kappaB, and expression of the proinflammatory cytokines IL-1beta and TNF-alpha through PI3-K-dependent pathways. ⋯ In PI3-Kgamma(-/-) mice, lung edema, neutrophil recruitment, nuclear translocation of NF-kappaB, and pulmonary levels of IL-1beta and TNF-alpha were significantly lower after endotoxemia as compared with PI3-Kgamma(+/+) controls. Among neutrophils that did accumulate in the lungs of the PI3-Kgamma(-/-) mice after endotoxin administration, activation of NF-kappaB and expression of proinflammatory cytokines was diminished compared with levels present in lung neutrophils from PI3-Kgamma(+/+) mice. These results show that PI3-K, and particularly PI3-Kgamma, occupies a central position in regulating endotoxin-induced neutrophil activation, including that involved in ALI.
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We investigated activation of mitogen-activated protein kinase (MAPK) subtype cascades in human neutrophils stimulated by IL-1beta. IL-1beta induced phosphorylation and activation of p38 MAPK and phosphorylation of MAPK kinase-3/6 (MKK3/6). Maximal activation of p38 MAPK was obtained by stimulation of cells with 300 U/ml IL-1beta for 10 min. ⋯ Combined stimulation of neutrophils with IL-1beta and G-CSF, a selective activator of the ERK cascade, resulted in the additive effects when the priming effect and phosphorylation of p38 MAPK and ERK were assessed. IL-1beta induced phosphorylation of ERK and JNK as well as p38 MAPK in human endothelial cells. These findings suggest that 1) in human neutrophils the MKK3/6-p38 MAPK cascade is selectively activated by IL-1beta and activation of this cascade mediates IL-1beta-induced O(2)(-) release and up-regulation of CD11b and CD15, and 2) the IL-1R-p38 MAPK pathway and the G-CSF receptor-ERK pathway work independently for activation of neutrophils.
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The effects of rabbit-derived polyclonal Ab against PcrV, a protein involved in the translocation of type III secreted toxins of Pseudomonas aeruginosa, was investigated in two animal models of P. aeruginosa sepsis. In a mouse survival study, the i.v. administration of anti-PcrV IgG after the airspace instillation of a lethal dose of P. aeruginosa resulted in the complete survival of the animals. ⋯ These results document that the therapeutic administration of anti-PcrV IgG blocks the type III secretion system-mediated virulence of P. aeruginosa and prevents septic shock and death, and that these protective effects are largely Fc independent. We conclude that Ab therapy neutralizing the type III secretion system has significant potential against lethal P. aeruginosa infections.
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Proliferative signaling by the IL-2R can occur through two distinct pathways, one mediated by Stat5 and one by the adaptor protein Shc. Although Stat5 induces T cell proliferation by serving as a transcription factor, the mechanism of proliferative signaling by Shc is poorly defined. We examined the roles of two major signaling pathways downstream of Shc, the p44/p42 mitogen-activated protein kinase (extracellular signal-related kinase (Erk)) and phosphatidylinositol 3-kinase (PI3K) pathways, in promitogenic gene induction and proliferation in the IL-2-dependent T cell line CTLL-2. ⋯ Moreover, mp110*ER induced modest levels of thymidine incorporation without subsequent cell division. Although insufficient for mitogenesis, mp110*ER enhanced Stat5-mediated proliferative signaling through a mechanism independent of Stat5 transcriptional activity. Thus, in addition to serving a necessary, but insufficient role in Shc-mediated promitogenic gene expression, the PI3K pathway contributes to T cell proliferation by potentiating mitogenic signaling by Stat5.
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The potent spasmogenic properties of IL-13 have identified this molecule as a potential regulator of airways hyperreactivity (AHR) in asthma. Although IL-13 is thought to primarily signal through the IL-13Ralpha1-IL-4Ralpha complex, the cellular and molecular components employed by this cytokine to induce AHR in the allergic lung have not been identified. By transferring OVA-specific CD4(+) T cells that were wild type (IL-13(+/+) T cells) or deficient in IL-13 (IL-13(-/-) T cells) to nonsensitized mice that were then challenged with OVA aerosol, we show that T cell-derived IL-13 plays a key role in regulating AHR, mucus hypersecretion, eotaxin production, and eosinophilia in the allergic lung. ⋯ By contrast, IL-13(+/+) T cells did not induce disease in STAT6-deficient mice. This shows that IL-13 employs a novel component of the IL-13 receptor signaling system that involves STAT6, independently of the IL-4Ralpha chain, to modulate pathogenesis. We show that this novel pathway for IL-13 signaling is dependent on T cell activation in the lung and is critically linked to downstream effector pathways regulated by eotaxin and STAT6.