Signal transduction and activation of the NADPH oxidase in eosinophils

Leukotriene B4, an endogenous stimulator of the innate immune response against pathogens

Leukotriene B4 (LTB4) is an endogenous lipid mediator of inflammation derived from arachidonic acid by the sequential action of cytosolic phospholipase A2 and 5-lipoxygenase. This mediator was initially recognized for its involvement in the recruitment of neutrophils. However, in the last decade, LTB4 has been clearly demonstrated to play a significant role in the control of microbial infections through its ability to activate host innate defenses. In this review, we will focus on the modulator effects of LTB4 on the innate defenses and discuss its therapeutic potential against viral pathogens.

Eosinophil recruitment and activation: the role of lipid mediators

Eosinophils are effector cells that migrate toward several mediators released at inflammatory sites to perform their multiple functions. The mechanisms driving eosinophil selective accumulation in sites of allergic inflammation are well-established and involve several steps controlled by adhesion molecules, priming agents, chemotactic, and surviving factors. Even though the majority of studies focused on role of protein mediators like IL-5 and eotaxins, lipid mediators also participate in eosinophil recruitment and activation. Among the lipid mediators with distinguish eosinophil recruitment and activation capabilities are platelet activating factor and the eicosanoids, including leukotriene B₄, cysteinyl leukotrienes, and prostaglandin D₂. In this review, we focused on the role of these four lipid mediators in eosinophil recruitment and activation, since they are recognized as key mediators of eosinophilic inflammatory responses.

Free radicals and antioxidants in inflammatory processes and ischemia-reperfusion injury

This article discusses the current understanding of the role of free radicals and antioxidants in inflammatory processes and in ischemia reperfusion injury. It begins by describing the manifestations of acute inflammation and outlining the cellular events that occur during inflammation. It then describes the biochemical mediators of inflammation with special attention to nitric oxide. It details the process of hypoxia reperfusion injury, the enzymes involved, its treatment, and studies involving specific hypoxia reperfusion injuries in various animal species.

Leukotrienes enhance the bactericidal activity of alveolar macrophages against Klebsiella pneumoniae through the activation of NADPH oxidase

Leukotrienes (LTs) are lipid mediators that participate in inflammatory diseases and innate immune function. We sought to investigate the importance of LTs in regulating the microbicidal activity of alveolar macrophages (AMs) and the molecular mechanisms by which this occurs. The role of LTs in enhancing AM microbicidal activity was evaluated pharmacologically and genetically using in vitro challenge with Klebsiella pneumoniae. Exogenous LTs increased AM microbicidal activity in a dose- and receptor-dependent manner, and endogenous production of LTs was necessary for optimal killing. Leukotriene B4 (LTB4) was more potent than cysteinyl LTs. An important role for nicotinamide adenine dinucleotide (NADPH) oxidase in LT-induced microbicidal activity was indicated by the fact that bacterial killing was abrogated by the NADPH oxidase inhibitor diphenyleneiodonium (DPI; 10 microM) and in AMs derived from gp91phox-deficient mice. By contrast, LT-induced microbicidal activity was independent of the generation of nitric oxide. LTs increased H2O2 production, and LTB4 was again the more potent agonist. Both classes of LTs elicited translocation of p47phox to the cell membrane, and LTB4 induced phosphorylation of p47phox in a manner dependent on protein kinase C-delta (PKC-delta) activity. In addition, the enhancement of microbicidal activity by LTs was also dependent on PKC-delta activity. Our results demonstrate that LTs, especially LTB4, enhanceAM microbicidal activity through the PKC-delta-dependent activation of NADPH oxidase.

Pharmacological comparison of LTB(4)-induced NADPH oxidase activation in adherent and non-adherent guinea-pig eosinophils

1. Leukotriene B(4) (LTB(4)) stimulation of guinea-pig peritoneal eosinophils, induced a biphasic activation of the NADPH oxidase composed of a rapid (<3 min) phase mediated by non-adherent cells and a sustained (3 - 120 min) phase mediated by CD11b/CD18 adherent eosinophils. Studies were undertaken to compare the intracellular mechanism that mediate these responses. 2. SB 203580 and PP1, inhibitors of p38 mitogen-activated protein (MAP) kinase and the src-family protein tyrosine kinases, respectively caused concentration-dependent attenuation of both the rapid (SB203580: pD(2)=-6.31; PP1: pD(2)=-5.50) and sustained (SB203580: pD(2)=-6.50; PP1: pD(2)=-5.73) phases. Similarly, the MAP kinase kinase-1 inhibitor, PD098059 produced partial inhibition of the both phases of superoxide generation. 3. The protein kinase C (PKC) inhibitors Ro-31 8220, GF 109203X and Gö 6976 attenuated the rapid NADPH oxidase response (pD(2)s=-6.10, -6.72, -6.15 respectively) and, to a lesser extent, (pD(2)s=-5.54, -6.02, -6.51 respectively) the sustained phase. 4. An inhibitor of phosphatidylinositol 3-kinase (PtdIns 3-kinase), wortmannin caused concentration dependent attenuation of the sustained (pD(2)=-8.68) but not rapid phase of superoxide generation. In contrast, the syk kinase inhibitor, piceatannol abolished the rapid (pD(2)=-6.43) but not sustained respiratory responses. 5. This study demonstrates that LTB(4)-induced superoxide generation from adherent and non-adherent eosinophils is mediated via both common (p38 MAP kinase, MEK-1, PKC and the src kinases) and divergent intracellular pathways (syk kinases and PtdIns 3-kinase). This suggests the possibility of therapeutic intervention to selective attenuate activation of adherent tissue eosinophils.

Pleiotropic role of lyn kinase in leukotriene B4–induced eosinophil activation

The authors have examined the role of the src-family of protein tyrosine kinases in leukotriene B4(LTB4)–induced activation of guinea-pig eosinophils. Western blot analysis identified the src-like protein tyrosine kinases p53lyn, p56lyn, p56/59hck, p55fgr, and p56lck whereas p60src, p62yes, p55blk, and p59fyn were not detected. LTB4 promoted a rapid increase in p53/56lyn activity in eosinophils, which peaked at 5 seconds and remained elevated at 60 seconds; hck, fgr, and lck were not activated. A role for p53/56lyn in eosinophil activation was investigated with the use of the src-selective inhibitor PP1 (1 μmol/L to 10 μmol/L), which attenuated LTB4-stimulated p53/56lyn activity and the phosphorylation of extracellular signal-regulated kinase–2 in intact cells. At comparable concentrations, PP1 was also shown to attenuate LTB4-induced nicotinamide adenine dinucleotide phosphate (reduced form) (NADPH) oxidase activation, chemotaxis, and Ca++-dependent [3H]arachidonic acid (AA) release. Moreover, an inhibitor of mitogen-activated protein kinase kinase-1, PD 098059, significantly inhibited LTB4-induced chemotaxis but had no effect on oxidant production or [3H]AA release. Collectively, these results implicate lyn kinase in LTB4-induced eosinophil activation through the recruitment of divergent cell-signaling pathways.

Pleiotropic role of lyn kinase in leukotriene B4–induced eosinophil activation

The authors have examined the role of the src-family of protein tyrosine kinases in leukotriene B4(LTB4)–induced activation of guinea-pig eosinophils. Western blot analysis identified the src-like protein tyrosine kinases p53lyn, p56lyn, p56/59hck, p55fgr, and p56lck whereas p60src, p62yes, p55blk, and p59fyn were not detected. LTB4 promoted a rapid increase in p53/56lyn activity in eosinophils, which peaked at 5 seconds and remained elevated at 60 seconds; hck, fgr, and lck were not activated. A role for p53/56lyn in eosinophil activation was investigated with the use of the src-selective inhibitor PP1 (1 μmol/L to 10 μmol/L), which attenuated LTB4-stimulated p53/56lyn activity and the phosphorylation of extracellular signal-regulated kinase–2 in intact cells. At comparable concentrations, PP1 was also shown to attenuate LTB4-induced nicotinamide adenine dinucleotide phosphate (reduced form) (NADPH) oxidase activation, chemotaxis, and Ca++-dependent [3H]arachidonic acid (AA) release. Moreover, an inhibitor of mitogen-activated protein kinase kinase-1, PD 098059, significantly inhibited LTB4-induced chemotaxis but had no effect on oxidant production or [3H]AA release. Collectively, these results implicate lyn kinase in LTB4-induced eosinophil activation through the recruitment of divergent cell-signaling pathways.