5-Oxo-eicosanoids are potent eosinophil chemotactic factors. Functional characterization and structural requirements

Biological Inactivation of 5-oxo-6,8,11,14-Eicosatetraenoic Acid by Human Platelets

Neutrophil-derived 5-oxo-6,8,11,14-eicosatetraenoic acid (5-oxo-ETE) is a potent activator of neutrophils and eosinophils. In the present study we examined the biosynthesis and metabolism of this substance by platelets. Although platelets contain an abundant amount of 5-hydroxyeicosanoid dehydrogenase, the enzyme responsible for the formation of 5-oxo-ETE, they synthesize only very small amounts of this substance from exogenous 5-hydroxyeicosatetraenoic acid (5-HETE) unless endogenous NADPH is converted to NADP+ by addition of phenazine methosulfate. Similarly, relatively small amounts of 5-oxo-ETE were formed by A23187-stimulated mixtures of platelets and neutrophils, which instead formed substantial amounts of two 12-hydroxy metabolites of this substance, 5-oxo-12-HETE and 8-trans-5-oxo-12-HETE, which were identified by comparison with authentic chemically synthesized compounds. These metabolites were also formed from 5-oxo-ETE by platelets stimulated with thrombin or A23187. In contrast, unstimulated platelets converted 5-oxo-ETE principally to 5-HETE. Neither 5-oxo-12-HETE nor 8-trans-5-oxo-12-HETE had appreciable effects on neutrophil calcium levels or platelet aggregation at concentrations as high as 10 μmol/L, but both blocked 5-oxo-ETE–induced calcium mobilization in neutrophils with IC50 values of 0.5 and 2.5 μmol/L, respectively. We conclude that platelets can biologically inactivate 5-oxo-ETE. Unstimulated platelets convert 5-oxo-ETE to 5-HETE, with a 99% loss of biological potency, whereas stimulated platelets convert this substance to 12-hydroxy metabolites, which possess antagonist properties.

5-oxo-6,8,11,14-eicosatetraenoic acid is a potent stimulator of L-selectin shedding, surface expression of CD11b, actin polymerization, and calcium mobilization in human eosinophils

5-oxo-6,8,11,14-eicosatetraenoic acid (5-oxo-ETE) is a metabolite of arachidonic acid formed by the oxidation of 5-hydroxy-6,8,11, 14-eicosatetraenoic acid by a highly specific dehydrogenase. 5-oxo-ETE is a chemoattractant for both neutrophils and eosinophils. Although it is not as effective as leukotriene B4 (LTB4) and platelet-activating factor (PAF) in stimulating neutrophil migration, we found that it is considerably more active than these and a variety of other lipid mediators as an eosinophil chemoattractant. Moreover, low concentrations of 5-oxo-ETE appear to enhance the responsiveness of these cells to PAF. The objectives of the current investigation were to identify rapid responses induced in eosinophils by 5-oxo-ETE that might be related to the infiltration of these cells into tissues. We found that 5-oxo-ETE is more effective than PAF and LTB4 in inducing both L-selectin shedding and actin polymerization in human eosinophils, whereas PAF is the most active of these mediators in stimulating calcium mobilization. The complementary effects of 5-oxo-ETE and PAF on actin polymerization and calcium mobilization may explain their synergistic effect on eosinophil migration. 5-oxo-ETE and PAF were equipotent in stimulating the surface expression of the beta2-integrin CD11b, but were slightly less potent than LTB4. 5-oxo-ETE- induced actin polymerization was subject to homologous but not heterologous desensitization. It was not prevented by incubation of eosinophils with inhibitors of protein kinase C (staurosporine), mitogen-activated protein kinase kinase (PD98059), or phosphatidylinositol-3-kinase (wortmannin). In conclusion, 5-oxo-ETE is a potent activator of human eosinophils and may be an important regulator of tissue infiltration of these cells.

5-oxo-ETE induces pulmonary eosinophilia in an integrin-dependent manner in Brown Norway rats

We have shown previously that the 5-lipoxygenase product 5-oxo-6,8, 11,14-eicosatetraenoic acid (5-oxo-ETE) is a highly potent eosinophil chemoattractant in vitro. To determine whether this substance can induce pulmonary eosinophil infiltration in vivo, it was administered to Brown Norway rats by tracheal insufflation. Eosinophils were then counted in lung sections that had been immunostained with an antibody to eosinophil major basic protein. 5-Oxo-ETE induced a dramatic increase in the numbers of eosinophils (ED50, 2.5 microg) around the walls of the airways, which reached maximal levels (five times control levels) between 15 and 24 h after administration, and then declined. LTB4 also induced pulmonary eosinophil infiltration with a similar ED50 but appeared to be somewhat less effective. In contrast, LTD4 and LTE4 were inactive. 5-Oxo-ETE-induced eosinophilia was unaffected by the LTB4 and PAF antagonists LY255283 and WEB 2170, respectively. However, it was inhibited by approximately 75% by monoclonal antibodies to CD49d (VLA-4) or CD11a (LFA-1) but was not significantly affected by an antibody to CD11b (Mac-1). In conclusion, 5-oxo-ETE induces pulmonary eosinophilia in Brown Norway rats, raising the possibility that it may be a physiological mediator of inflammation in asthma.

Receptors for the 5-oxo class of eicosanoids in neutrophils

5-Hydroxy- and 5-oxo-eicosatetraenoate (5-HETE and 5-oxoETE) activate polymorphonuclear neutrophils (PMNs) through a common, receptor-like recognition system. To define this system, we examined the interaction of these eicosanoids with human PMNs. PMNs esterified 5-[3H]HETE to glycerolipids at 37 and 4 degreesC. At 37 but not 4 degreesC, the cells also hydroxylated the label to 5, 20-[3H]diHETE. The acyl:CoA synthetase blocker, triacsin C, inhibited esterification but also led to an increase in the hydroxylation of the label. PMNs processed 5-[3H]oxoETE through the same pathways but only or principally after reducing it to 5-[3H]HETE (37 or 4 degreesC). In the presence of these varying metabolic reactions, PMNs (37 or 4 degreesC; +/- triacsin C) could not be shown to receptor bind either radiolabel. Plasma membranes isolated from PMNs esterified but unlike whole cells did not reduce or hydroxylate 5-[3H]oxoETE. Triacsin C blocked esterification, thereby rendering the membranes unable to metabolize this radiolabel. Indeed, triacsin C-treated membranes bound (Kd = 3.8 nM) 5-[3H]oxoETE specifically and reversibly to 86 pmol of sites per 25 micrograms of membrane protein. 5-OxoETE, 5-HETE, and 5,15-diHETE displaced this binding at concentrations correlating with their potency in eliciting PMN Ca2+ transients. GTP and GTPgammaS, but not ATP or ATPgammaS, also reduced 5-[3H]oxoETE binding, whereas 15-HETE, leukotriene B4, platelet-activating factor, IL-8, C5a, and N-formyl-Met-Leu-Phe lacked this effect. We conclude that PMNs and their plasma membranes use an acyl:CoA synthetase-dependent route to esterify 5-HETE and 5-oxoETE into lipids. Blockade of the synthetase uncovers cryptic plasmalemma sites that bind 5-oxoETE with exquisite specificity. These sites apparently mediate responses to the 5-oxo class of eicosanoids and are likely members of the serpentine superfamily of G protein-linked receptors.

Calcium/calmodulin-dependent conversion of 5-oxoeicosanoids to 6, 7-dihydro metabolites by a cytosolic olefin reductase in human neutrophils

We previously showed that 6-trans isomers of leukotriene B4 but not leukotriene B4 itself are converted to dihydro metabolites by human neutrophils. The first step in the formation of these metabolites is oxidation of the 5-hydroxyl group by 5-hydroxyeicosanoid dehydrogenase. The objective of the present investigation was to characterize the second step in the formation of the dihydro metabolites, reduction of an olefinic double bond. We found that the olefin reductase reduces the 6,7-double bond of 5-oxoeicosanoids, is localized in the cytosolic fraction of neutrophils, and requires NADPH as a cofactor. Neutrophil cytosol converts a variety of both 5-oxo- and 15-oxoeicosanoids to dihydro products. However, conversion of 5-oxoeicosanoids to their 6,7-dihydro metabolites is inhibited by EGTA and a calmodulin antagonist and stimulated by the addition of calcium and calmodulin, whereas the reduction of 15-oxoeicosanoids to their 13,14-dihydro metabolites is slightly inhibited by calcium. Furthermore, eicosanoid Delta6- and Delta13-reductases could be separated by chromatography on DEAE-Sepharose. 5-Oxo-6,8,11,14-eicosatetraenoic acid (5-oxo-ETE) is converted by the Delta6-reductase to 6,7-dihydro-5-oxo-ETE, which is 1000 times less potent than 5-oxo-ETE in mobilizing calcium in neutrophils. We conclude that neutrophils contain both 5-oxoeicosanoid Delta6-reductase and prostaglandin Delta13-reductase. Metabolism of 5-oxo-ETE by the Delta6-reductase results in loss of its biological activity.

Human ecalectin, a variant of human galectin-9, is a novel eosinophil chemoattractant produced by T lymphocytes

A 1.6-kilobase pair cDNA was isolated from a human T-cell-derived expression library that encodes a novel eosinophil chemoattractant (designated ecalectin) expressed during allergic and parasitic responses. Based on its deduced amino acid sequence, ecalectin is a 36-kDa protein consisting of 323 amino acids. Although ecalectin lacks a hydrophobic signal peptide, it is secreted from mammalian cells. Ecalectin is not related to any known cytokine or chemokine but rather is a variant of human galectin-9, a member of the large family of animal lectins that have affinity for beta-galactosides. Recombinant ecalectin, expressed in COS cells and insect cells, exhibited potent eosinophil chemoattractant activity and attracted eosinophils in vitro and in vivo in a dose-dependent manner but not neutrophils, lymphocytes, or monocytes. The finding that the ecalectin transcript is present in abundance in various lymphatic tissues and that its expression increases substantially in antigen-activated peripheral blood mononuclear cells suggests that ecalectin is an important T-cell-derived regulator of eosinophil recruitment in tissues during inflammatory reactions. We believe that this is the first report of the expression of an immunoregulatory galectin expressed by a T-cell line that is selective for eosinophils.

Eotaxin-2 activates chemotaxis-related events and release of reactive oxygen species via pertussis toxin-sensitive G proteins in human eosinophils

Eosinophils play an important role in allergic and autoimmune diseases. They are activated by distinct chemokines, leading to the immigration into the inflamed tissue, and mediate tissue damage by releasing reactive oxygen species. Recently, eotaxin was found to have the broadest spectrum of activities of all eosinophil-activating CC chemokines. In this study we investigated the effect of the novel CC chemokine, eotaxin-2, on eosinophil effector functions and compared its activity with eotaxin. Using nitrobenzoxadiazole-phallacidin staining and flow cytometry, we show that eotaxin-2 induced rapid and transient actin polymerization, a prerequisite for cell migration and modulation of the respiratory burst, in eosinophils in the same range of efficacy as observed for eotaxin. Eotaxin-2 induced the release of reactive oxygen species in a dose-dependent manner; half maximal and maximal release were found at 50 ng/ml and 500 ng/ml, respectively. Surprisingly, the efficacy of eotaxin-2 was comparable to that of eotaxin and C5a. Release of reactive oxygen species was inhibited by pertussis toxin, indicating the involvement of Gi proteins in the signaling of eotaxin-2. Moreover, the anti-CC chemokine receptor 3 (CCR3) monoclonal antibody, 7B11, was able to inhibit transient rise in the cytosolic Ca2+ concentration and the release of reactive oxygen species following stimulation with eotaxin-2. Therefore, eotaxin-2 represents a potent CC chemokine for human eosinophils activating chemotaxis-related events, such as actin polymerization, and the respiratory burst via the CCR3. Moreover, the efficacy of eotaxin-2 seems to be in the same range as that of eotaxin which might re-evaluate the recent profile of activity of CC chemokines in the activation of human eosinophils.

Electrospray mass spectrometric analysis of 5-hydroperoxy and 5-hydroxyeicosatetraenoic acids generated by lipid peroxidation of red blood cell ghost phospholipids

Recent evidence suggests that generation of hydroxyl radicals in the presence of lipid membranes can lead to oxidation of arachidonic acid esterified to glycerophospholipids and the production of compounds isomeric to prostaglandins, thromboxanes, and leukotrienes. Liquid chromatography tandem mass spectrometry and multiple reaction monitoring were employed to quantitate the production of 5-hydroxyeicosatetraenoic acid (5-HETE), 5-hydroperoxyeicosatetraenoic acid (5-HPETE), and 5-oxo-eicosatetraenoic acid (5-oxo-ETE) in red blood cells ghosts treated with t-butylhydroperoxide (tBuOOH). Untreated red blood cell ghosts were found to contain low, but measurable quantities of these three 5-oxygenated eicosanoids as phospholipid esters. Following treatment, there was approximately a 53- and 22.5-fold increase in 5-HETE and 5-HPETE, respectively, and an 8.5-fold increase in 5-oxo-ETE. The formation of these compounds was inhibited nearly 90% by the antioxidants butylated hydroxytoluene, ascorbic acid, and resveratrol providing further evidence for free radical mediated oxidation of arachidonic acid. This analytical protocol provided sufficient sensitivity for detection of these compounds in studies in which previous analysis by high-pressure liquid chromatography with UV detection failed to detect their presence. These results reveal that the biologically active eicosanoids 5-HPETE, 5-HPETE, and 5-oxo-ETE are formed esterified to phospholipids following exposure of cellular membranes to reactive oxygen species and free radicals in a model system where intracellular antioxidant mechanisms were depleted.

Secretoneurin, a Novel Neuropeptide, Is a Potent Chemoattractant for Human Eosinophils

Secretoneurin (SN), a 33-amino acid neuropeptide, is derived from secretogranin II that is released from sensory afferent C-fibers by capsaicin. Described functions of secretoneurin include chemotaxis of monocytes and endothelial cells, and inhibition of endothelial cell proliferation. Inhibition of monocyte chemotaxis by staurosporine indicated involvement of specific signaling pathways. We have tested effects of SN, substance P (SP), and interleukin-8 (IL-8) on eosinophil migration in modified Boyden chambers including signaling mechanisms of neuropeptide and cytokine stimulation of human eosinophils. Experiments showed SN as eosinophil chemoattractant comparable in its potency to IL-8. Checkerboard analysis, usage of a specific anti–SN-antibody, and receptor desensitization experiments confirmed the chemotactic activity. Preincubation of the cells with effective concentrations of staurosporine or tyrphostin-23 showed no effect, whereas treatment with wortmannin (WTN) or 3-isobutyl-1-methylxantin (IBMX) completely blocked SN-induced migration. Additionally, experiments ruled out tyrphostin-23- and WTN-sensitive signaling pathways for SP-induced chemotaxis of eosinophils. We conclude that SN-stimulated human eosinophil chemotaxis is mediated via a unique and specific signal transduction pathway that involves activation of phosphodiesterases and WTN-sensitive enzymes, ie, phospholipase D and phosphatidylinositol-3-kinase. In contrast, we report that activation of the latter and tyrosine kinases is required for SP-induced chemotaxis of eosinophils.

Secretoneurin, a Novel Neuropeptide, Is a Potent Chemoattractant for Human Eosinophils

Secretoneurin (SN), a 33-amino acid neuropeptide, is derived from secretogranin II that is released from sensory afferent C-fibers by capsaicin. Described functions of secretoneurin include chemotaxis of monocytes and endothelial cells, and inhibition of endothelial cell proliferation. Inhibition of monocyte chemotaxis by staurosporine indicated involvement of specific signaling pathways. We have tested effects of SN, substance P (SP), and interleukin-8 (IL-8) on eosinophil migration in modified Boyden chambers including signaling mechanisms of neuropeptide and cytokine stimulation of human eosinophils. Experiments showed SN as eosinophil chemoattractant comparable in its potency to IL-8. Checkerboard analysis, usage of a specific anti–SN-antibody, and receptor desensitization experiments confirmed the chemotactic activity. Preincubation of the cells with effective concentrations of staurosporine or tyrphostin-23 showed no effect, whereas treatment with wortmannin (WTN) or 3-isobutyl-1-methylxantin (IBMX) completely blocked SN-induced migration. Additionally, experiments ruled out tyrphostin-23- and WTN-sensitive signaling pathways for SP-induced chemotaxis of eosinophils. We conclude that SN-stimulated human eosinophil chemotaxis is mediated via a unique and specific signal transduction pathway that involves activation of phosphodiesterases and WTN-sensitive enzymes, ie, phospholipase D and phosphatidylinositol-3-kinase. In contrast, we report that activation of the latter and tyrosine kinases is required for SP-induced chemotaxis of eosinophils.

Cutting Edge: Detection of MCP-4 in Dermal Fibroblasts and Its Activation of the Respiratory Burst in Human Eosinophils

CC-chemokines are an important family of proinflammatory mediators that promote the recruitment and activation of human eosinophils in chronic inflammatory diseases. Recently, a novel human CC-chemokine, monocyte chemotactic protein 4 (MCP-4), has been reported that shows amino acid sequence similarities with eotaxin and RANTES, induces chemotaxis of eosinophils, and signals through specific chemokine receptors. In this study, we investigated the effect of MCP-4 on different eosinophil effector functions leading to the activation of the respiratory burst. In human eosinophils, MCP-4 dose dependently induced the production of reactive oxygen species and actin polymerization as a related event. Pretreatment of eosinophils with different enzyme inhibitors interacting with the signal transduction cascade revealed that Gi protein, protein kinase C, tyrosine kinase, and phosphatidylinositol-3-kinase are involved in the signaling following stimulation with MCP-4. In addition, cytokine-stimulated human dermal fibroblasts expressed high levels of MCP-4 mRNA, suggesting that fibroblasts are a physiologic source of MCP-4. Therefore, this study demonstrates that there is an important role of MCP-4 in the activation of eosinophils and that the interaction between dermal fibroblasts and human eosinophils may play an important role within the cytokine network.

The CC chemokine antagonist Met-RANTES inhibits eosinophil effector functions through the chemokine receptors CCR1 and CCR3

Eosinophils are predominant effector cells not only in allergic diseases but also in connective tissue diseases. The recruitment of eosinophils to the site of inflammation and release of reactive oxygen species leading to tissue damage and propagation of the inflammatory response are mediated by chemokines. Thus, agents that would be able to inhibit or antagonize chemokine-induced eosinophil activation are interesting as therapeutical agents. We describe the effect of a chemokine receptor antagonist, Met-RANTES, on human eosinophil effector functions in response to RANTES, monocyte chemoattractant protein (MCP)-3 and eotaxin. Met-RANTES was able to inhibit dose-dependently [Ca2+]i transients in eosinophils following stimulation with RANTES, MCP-3 and eotaxin. Whereas maximal and half-maximal inhibitory effect of Met-RANTES following stimulation with RANTES and MCP-3 were observed at 2 micrograms/ml and 1 microgram/ml, respectively, maximal and half-maximal inhibitory effects of Met-RANTES in response to eotaxin were detected at 10 micrograms/ml and 3 micrograms/ml. Moreover, eotaxin-induced [Ca2+]i transients were only half reduced at a Met-RANTES concentration at which RANTES and MCP-3 were completely blocked. Besides its effect on [Ca2+]i transients, Met-RANTES dose-dependently inhibited actin polymerization in eosinophils following chemokine stimulation. Whereas Met-RANTES totally inhibited RANTES- and MCP-3-induced actin polymerization at 5 micrograms/ml, the eotaxin-induced response was only reduced by 50%. However, Met-RANTES inhibited dose-dependently the release of reactive oxygen species in response to RANTES, MCP-3 and eotaxin. Again, eotaxin-induced release of reactive oxygen species, however, was only half reduced at a Met-RANTES concentration (10 micrograms/ml) at which RANTES and MCP-3 were completely blocked. The results of this study show that (1) Met-RANTES is an effective and powerful antagonist of effector functions of human eosinophils following stimulation with RANTES, MCP-3 and eotaxin; (2) Met-RANTES seems to be able to antagonize the response of eosinophils through chemokine receptor 1 (CCR1) preferentially to CCR3; (3) Met-RANTES antagonizes eosinophil but not neutrophil effector functions and might be therefore of interest for a new therapeutical approach to prevent the invasion and destructive power of eosinophils in diseases that are accompanied by eosinophil infiltration such as allergic asthma and connective tissue diseases.

High-pressure liquid chromatography of oxo-eicosanoids derived from arachidonic acid

Eicosanoids are a large group of biologically active metabolites of arachidonic acid and related C20 fatty acids. Many of these compounds contain hydroxyl groups which can be converted to oxo groups by a variety of substrate-specific dehydrogenases. In many cases, this results in a reduction in potency, but in others, such as the oxidation of 5-hydroxyeicosatetraenoic acid to its oxo metabolite 5-oxo-eicosatetraenoic acid, there is a dramatic increase in biological activity. Thus, it is often very important to analyze the relative amounts of oxo- and hydroxy-eicosanoids formed by various cells and tissues. The present study was designed to compare the chromatographic behavior of oxo-eicosanoids and their hydroxy counterparts in commonly used mobile phases for reversed-phase and normal-phase HPLC. We examined three groups of eicosanoids: prostaglandins, leukotriene B4 and some of its metabolites, and monohydroxy-eicosanoids and their oxo metabolites. We found that in reversed-phase HPLC, the retention times of oxo-eicosanoids were longer than those of the corresponding hydroxy-eicosanoids in mobile phases containing acetonitrile as the major organic component, whereas the reverse was true for mobile phases containing methanol. Normal-phase HPLC using mobile phases containing hexane, isopropanol, and acetic acid gave excellent separation of oxo- and hydroxy-eicosanoids. Increasing the concentration of acetic acid in the mobile phase selectively reduced the retention times of oxo-eicosatetraenoic acids compared to monohydroxy-eicosatetraenoic acids, whereas the reverse was true for isopropanol. Differences in the chromatographic behavior of oxo- and hydroxy-eicosanoids can be useful clues in the structural characterization of these compounds, as illustrated by the chromatographic properties of a complex series of LTB4 metabolites formed by rat neutrophils.

Chemotactic 5-oxo-eicosatetraenoic acids induce oxygen radical production, Ca2+-mobilization, and actin reorganization in human eosinophils via a pertussis toxin-sensitive G-protein

The arachidonic acid metabolites 5-oxo-[6E,8Z,11Z,14Z]-eicosatetraen oic acid (5oETE) and 5-oxo-15-hydroxy-[6E,8Z,11Z,13E]-eicosatetrae noi c acid (5oHETE) are potent eosinophil chemotaxins. Here, the activation profile of 5-oxo-eicosanoids in eosinophils was further characterized and compared to other eosinophil activators such as complement fragment C5a (C5a), platelet-activating factor (PAF), interleukin-5 (IL-5), and phorbol ester (PMA). Flow cytometric studies revealed a rapid and transient actin polymerization upon stimulation by both 5-oxo-eicosanoids. Desensitization studies using actin polymerization as the parameter indicated cross-desensitization between the two 5-oxo-eicosanoids but revealed no interference with the response to other chemotaxins. Fluorescence measurements with Fura-2-labeled eosinophils in the presence of EGTA indicated Ca2+-mobilization from intracellular stores by 5oETE and 5oHETE. Both 5-oxo-eicosanoids stimulated the production of reactive oxygen metabolites as demonstrated by lucigenin-dependent chemiluminescence, superoxide dismutase-inhibitable cytochrome C reduction, and flow cytometric dihydrorhodamine-123 analysis. At optimal concentrations the changes induced by 5-oxo-eicosanoids were comparable to those obtained by C5a and PAF, whereas IL-5 and PMA induced only a restricted pattern of cell responses. Cell responses elicited by 5-oxo-eicosanoids were inhibited by pertussis toxin, indicating coupling of the putative 5-oxo-eicosanoid-receptor to G-proteins. These results indicate that 5-oxo-eicosanoids are stong activators of eosinophils with comparable biologic activity to the eosinophil chemotaxins C5a and PAF. These findings point to a role of 5-oxo-eicosanoids in the pathogenesis of eosinophilic inflammation as chemotaxins as well as activators of pro-inflammatory activities.

Human eotaxin represents a potent activator of the respiratory burst of human eosinophils

Increased numbers of eosinophils are found in parasitic infections, autoimmune diseases and allergic diseases such as allergic asthma. They are activated by distinct cytokines and chemokines leading to the immigration in the inflamed tissue and mediate tissue damage by releasing reactive oxygen species. Here, the effect of the recently cloned CC chemokine human eotaxin was investigated for its ability to affect different eosinophil effector functions and compared to the CC chemokines MCP-3 and RANTES. Human eotaxin induced chemotaxis of human eosinophils in a dose-dependent manner. The range of efficacy of the CC chemokines compared to the well-known chemotaxin C5a was eotaxin = RANTES > MCP-3 = C5a. In addition, eotaxin induced rapid and transient actin polymerization, a prerequisite for cell migration, in eosinophils in the same range of efficacy as observed for chemotaxis. To investigate whether eotaxin was able to activate the respiratory burst of eosinophils, release of reactive oxygen species was measured by lucigenin-dependent chemiluminescence. Eotaxin induced production of significantly high amounts of reactive oxygen species at a concentration between 10 ng/ml and 500 ng/ml. Surprisingly, the effect of eotaxin was comparable to the well-known eosinophil activator C5a. The range of efficacy of the CC chemokines compared to C5a in the activation of the respiratory burst was eotaxin = C5a > MCP-3 > RANTES. Production of reactive oxygen species was inhibited by pertussis toxin, staurosporin, genestein and wortmannin. Furthermore, eotaxin induced transient increases in intracellular calcium concentration ([Ca2+]i) in human eosinophils. Therefore, pertussis toxin-sensitive Gi-proteins, protein kinase C, tyrosine kinase, phosphatidylinositol-3-kinase and transient increases in [Ca2+]i are involved in the signal transduction of eosinophils following stimulation with eotaxin. In summary, this study reveals the importance of the CC chemokine eotaxin as a potent activator of the respiratory burst, actin polymerization and chemotaxis. Eotaxin, therefore, plays an important role not only by attracting eosinophils to the site of inflammation but also by damaging tissue by its capacity to induce the release of reactive oxygen species.

Dermatophytes contain a novel lipid-like leukocyte activator

In the early phase of dermatophytosis, neutrophils are regularly detected microscopically in the infected skin. Although neutrophil recruitment may at least in part occur indirectly by complement activation, we asked whether dermatophytes might release chemoattractants for neutrophils. We cultivated various strains of different dermatophytes and tested fungal extracts for the presence of neutrophil chemotactic activity. As a result, we detected neutrophil chemotactic activity only in diethylether extracts, but not in aqueous extracts. We purified this lipid-like leukocyte activator (LILA) to apparent homogeneity by reversed-phase high performance liquid chromatography and found that purified LILA does not show ultraviolet absorption at wavelengths > 210 nm. Biologic studies revealed that LILA is as effective as formyl-methionyl-leucyl-phenylalanine in eliciting neutrophil chemotaxis, degranulation, and activation of the respiratory burst. Desensitization experiments in chemotaxis and degranulation with leukotriene B4, platelet-activating factor, or 5-oxo-eicosanoids revealed that LILA does not cross-desensitize with any of these other lipid-like attractants and thus possibly acts via a distinct as yet postulated neutrophil receptor. It is hypothesized that LILA, similarly to formylated methionyl peptides in bacteria, represents a dermatophyte- and possibly fungus-specific lipid compound that allows the host phagocytes to specifically recognize fungal infection. This system would be similar to the recognition of bacteria by phagocytes via N-formylated methionyl peptides, which represent a characteristic and unique system to identify bacteria.

Chemotactic 5-oxo-icosatetraenoic acids activate a unique pattern of neutrophil responses. Analysis of phospholipid metabolism, intracellular Ca2+ transients, actin reorganization, superoxide-anion production and receptor up-regulation

Neutrophil cell responses and signal pathways elicited by the chemotactic arachidonic acid metabolites (6E, 8Z, 11Z, 14Z)-5-oxo-icosatetraenoic acid and (6E, 8Z, 11Z, 13E)-5-oxo-15-hydroxy-icosatetraenoic acid were studied and compared with those of other chemotaxins. Polyphosphoinositol lipid analysis revealed activation of phosphatidylinositol-biphosphate 3-kinase by both agonists. Experiments with Fura-2 in the presence of EGTA indicated Ca2+ mobilization from intracellular stores by both 5-oxo-icosanoids. A transient actin response and production of small amounts of superoxide anions upon stimulation with both agents was detected. The changes induced by 5-oxo-icosanoids were more moderate and transient than those obtained by other chemotaxins. Desensitization studies indicated cross-desensitization between both 5-oxo-icosanoids, but no interference with the response of other chemotaxins. All cell responses elicited by 5-oxo-icosanoids at concentrations 500-fold higher than the ED50 of other functions did not induce up-regulation of CD11b and N-formyl-peptide receptors at the cell surface, and failed to potentiate N-formyl-peptide-induced superoxide anion production. These results indicate that 5-oxo-icosanoids trigger a unique pattern of neutrophil responses.