Leukotriene B4-induced neutrophil extracellular traps impede the clearance of Pneumocystis.

Pneumocystis pneumonia (PCP) is a fungal pulmonary disease with high mortality in immunocompromised patients. Neutrophils are essential in defending against fungal infections; however, their role in PCP is controversial. Here we aim to investigate the effects of neutrophil extracellular traps (NETs) on Pneumocystis clearance and lung injury using a mouse model of PCP. Intriguingly, although neutrophils play a fundamental role in defending against fungal infections, NETs failed to eliminate Pneumocystis, but instead impaired the killing of Pneumocystis. Mechanically, Pneumocystis triggered Leukotriene B4 (LTB4)-dependent neutrophil swarming, leading to agglutinative NET formation. Blocking Leukotriene B4 with its receptor antagonist Etalocib significantly reduced the accumulation and NET release of neutrophils in vitro and in vivo, enhanced the killing ability of neutrophils against Pneumocystis, and alleviated lung injury in PCP mice. This study identifies the deleterious role of agglutinative NETs in Pneumocystis infection and reveals a new way to prevent NET formation, which provides new insights into the pathogenesis of PCP.

Purinergic signaling: A new front-line determinant of resistance and susceptibility in leishmaniasis.

Leishmaniasis is a neglected tropical disease that causes several clinical manifestations. Parasites of the genus Leishmania cause this disease. Spread across five continents, leishmaniasis is a particular public health problem in developing countries. Leishmania infects phagocytic cells such as macrophages, where it induces adenosine triphosphate (ATP) release at the time of infection. ATP activates purinergic receptors in the cell membranes of infected cells and promotes parasite control by inducing leukotriene B4 release and NLRP3 inflammasome activation. Moreover, uridine triphosphate induces ATP release, exacerbating the immune response. However, ATP may also undergo catalysis by ectonucleotidases present in the parasite membrane, generating adenosine, which activates P1 receptors and induces the production of anti-inflammatory molecules such as prostaglandin E2 and IL-10. These mechanisms culminate in Leishmania's survival. Thus, how Leishmania handles extracellular nucleotides and the activation of purinergic receptors determines the control or the dissemination of the disease.

Effect of lysed and non-lysed sickle red cells on the activation of NLRP3 inflammasome and LTB4 production by mononuclear cells.

OBJECTIVE AND DESIGN: This study tested the hypothesis that sickle red blood cell (SS-RBC) can induce inflammasome NLRP3 components gene expression in peripheral blood mononuclear cells (PBMCs) as well as interleukin-1ß (IL-1ß) and leukotriene B4 (LTB4) production. Additionally, we investigated the effect of hydroxyurea (HU) treatment in these inflammatory markers. METHODS: PBMCs from healthy donors (AA-PBMC) were challenged with intact and lysed RBCs from SCA patients (SS-RBC) and from healthy volunteers (AA-RBC). NLRP3, IL-1ß, IL-18 and Caspase-1 gene expression levels were assessed by quantitative PCR (qPCR). IL-1ß protein levels and LTB4 were measured by ELISA. RESULTS: We observed that lysed SS-RBC induced the expression of inflammasome NLRP3 components, but this increase was more prominent for CASP1 and IL18 expression levels. Moreover, we observed that intact SS-RBC induced higher production of IL-1ß and LTB4 than lysed SS-RBC. Although SCA patients treated with HU have a reduction in NLRP3 gene expression and LTB4 production, this treatment did not modulate the expression of other inflammasome components or IL-1ß production. CONCLUSIONS: Thus, our data suggest that caspase-1, IL-1ß and IL-18 may contribute to the inflammatory status observed in SCA and that HU treatment may not interfere in this inflammatory pathway.

Eicosanoid production varies by sex in mesenteric ischemia reperfusion injury.

Intestinal ischemia/reperfusion (I/R)-induced injury is an inflammatory response with significant morbidity and mortality. The early inflammatory response includes neutrophil infiltration. However, the majority of rodent studies utilize male mice despite a sexual dimorphism in intestinal I/R-related diseases. We hypothesized that sex may alter inflammation by changing neutrophil infiltration and eicosanoid production. To test this hypothesis, male and female C57Bl/6 mice were subjected to sham treatment or 30 min intestinal ischemia followed by a time course of reperfusion. We demonstrate that compared to male mice, females sustain significantly less intestinal I/R-induced tissue damage and produced significant LTB4 concentrations. Male mice release PGE2. Finally, treatment with a COX-2 specific inhibitor, NS-398, attenuated I/R-induced injury, total peroxidase level, and PGE2 production in males, but not in similarly treated female mice. Thus, I/R-induced eicosanoid production and neutrophil infiltration varies between sexes suggesting that distinct therapeutic intervention may be needed in clinical ischemic diseases.

Microglia-released leukotriene B4 promotes neutrophil infiltration and microglial activation following intracerebral hemorrhage.

Intracerebral hemorrhage (ICH) from blood vessel rupture results in parenchymal hematoma formation and neuroinflammation, ultimately leading to neurodegeneration. Several lines of evidence suggest that the severity of ICH-induced neural damage is exacerbated by infiltration of T-cells, monocytes, and especially neutrophils into the hematoma. Neutrophil migration is regulated by chemokines, formyl peptides, and leukotriene B4 (LTB4), a metabolite of arachidonic acid. In this study, we demonstrate that LTB4 is a key signaling factor promoting microglial activity and leukocyte infiltration into hematoma and thus a potentially critical determinant of ICH pathogenesis and clinical outcome. Lipidomic analysis revealed markedly increased LTB4 concentration in the hematoma-containing brain tissues 6-24 h after experimental ICH in mice. Expression of 5-lipoxygenase, a rate-limiting enzyme for LTB4 production, was upregulated in activated microglia and neutrophils within the hematoma following ICH. Treatment of cultured BV-2 microglia with thrombin, which is abundant in hematoma, promoted activation, proinflammatory cytokine expression, and LTB4 secretion. Further, conditioned medium from thrombin-stimulated BV-2 cells potentiated the transwell migration of neutrophil-like cells, a response blocked by a LTB4 receptor antagonist. These results suggest that arachidonic acid conversion to LTB4 following ICH contributes to neuroinflammation and ensuing neural tissue damage by inducing microglial activation and neutrophil recruitment.

Lipidomics Profiling of Hidradenitis Suppurativa Skin Lesions Reveals Lipoxygenase Pathway Dysregulation and Accumulation of Proinflammatory Leukotriene B4.

Hidradenitis suppurativa (HS) is a chronic, recurring inflammatory dermatosis characterized by abscesses, deep-seated nodules, sinus tracts, and fibrosis in skin lesions around hair follicles of the axillary, inguinal, and anogenital regions. Whereas the exact pathogenesis remains poorly defined, clear evidence suggests that HS is a multifactorial inflammatory disease characterized by innate and adaptive immune components. Bioactive lipids are important regulators of cutaneous homeostasis, inflammation, and resolution of inflammation. Alterations in the lipid mediator profile can lead to malfunction and cutaneous inflammation. We used targeted lipidomics to analyze selected omega-3 and omega-6 polyunsaturated fatty acids in skin of patients with HS and of healthy volunteers. Lesional HS skin displayed enrichment of 5-lipoxygenase (LO)‒derived metabolites, especially leukotriene B4. In addition, 15-LO‒derived metabolites were underrepresented in HS lesions. Changes in the lipid mediator profile were accompanied by transcriptomic dysregulation of the 5-LO and 15-LO pathways. Hyperactivation of the 5-LO pathway in lesional macrophages identified these cells as potential sources of leukotriene B4, which may cause neutrophil influx and activation. Furthermore, leukotriene B4-induced mediators and pathways were elevated in HS lesions, suggesting a contribution of this proinflammatory lipid meditator to the pathophysiology of HS.

LTB4-induced anti-apoptosis and infiltration of neutrophils in rheumatoid arthritis.

Rheumatoid arthritis (RA) is the most common autoimmune disease, resulting in synovitis, joint pain and stiffness, even deformity and disability. The interactions between leukotriene B4 (LTB4) and neutrophils in RA progression have not been elucidated in detail. Our review focuses on the correlation of LTB4 and neutrophils in the development of RA especially in terms of infiltration and delayed life span of neutrophils. In this article, the roles of LTB4 in the anti-apoptosis of neutrophils will be detailed, which is achieved by suppressed pro-apoptotic Bax and up-regulated anti-apoptotic Mcl-1, and several key molecules, as well as signalling pathways and factors relevant to the enhancement of LTB4 production and functions. The mechanisms of LTB4-induced anti-apoptosis and infiltration of neutrophils provide more potential targets in the treatment of RA and recent therapeutic strategies are also discussed.

Anti-chemotactic activity in the secretory/excretory products of Lepeophtheirus salmonis.

The ectoparasite, Lepeophtheirus salmonis (Kroyer 1837), is effective at avoiding elimination from its host, Atlantic salmon, Salmo salar L., by inhibiting the recruitment of immune cells to the site of attachment. In other ectoparasitic arthropods, numerous factors have been identified that bind or neutralize chemokines preventing their interaction with receptors on the surfaces of immune cells. To determine if L. salmonis is utilizing a similar mechanism of immune modulation, the chemotactic activity of peripheral blood leukocytes (PBL) to leukotriene B4 (LTB4) and the secreted/excreted products (SEPs) of the sea louse were investigated in vitro. The results showed that incubation of LTB4 with SEPs reduced leukocyte migration compared to LTB4 immune stimulation alone. Data suggests that one of the mechanisms L. salmonis may be using to regulate immune cell recruitment in Atlantic salmon is by inhibiting or neutralizing the activity of chemokines.

Leukotriene B4 induces proliferation of rat pulmonary arterial smooth muscle cells via modulating GSK-3ß/ß-catenin pathway.

Leukotriene B4 (LTB4) has been found to contribute to pulmonary arterial smooth muscle cells (PASMCs) proliferation and pulmonary arterial remodeling therefore the development of pulmonary arterial hypertension (PAH). Yet, the underlying molecular mechanisms remain poorly understood. The present study aims to address this issue. Our results demonstrate that LTB4 dose- and time-dependently induced proliferation of primary cultured rat PASMCs, this was accompanied with the activation of phosphatidylinositol-3-kinase/Akt (PI3K/Akt) and extracellular signal-regulated kinase 1/2 (ERK1/2) signaling pathways, and consequent inactivation of glycogen synthase kinase-3ß (GSK-3ß), up-regulation of ß-catenin and induction of cyclin D1 expression. The presence of PI3K inhibitor (LY294002) or MEK inhibitor (U0126) or prior silencing of ß-catenin with siRNA suppressed LTB4-induced cyclin D1 up-regulation and PASMCs proliferation. In addition, inactivation or lack of GSK-3ß up-regulated ß-catenin and cyclin D1 in PASMCs. Taken together, our study indicates that activation of PI3K/Akt and ERK1/2 pathways mediates LTB4-induced PASMCs proliferation by modulating GSK-3ß/ß-catenin/cyclin D1 axis and suggests that targeting this pathway might have potential value in alleviating vascular remodeling and benefit PAH.

Mesenchymal Stem Cell-Derived Extracellular Vesicles Decrease Lung Injury in Mice.

Human mesenchymal stem cell (MSC) extracellular vesicles (EV) can reduce the severity of bacterial pneumonia, but little is known about the mechanisms underlying their antimicrobial activity. In the current study, we found that bacterial clearance induced by MSC EV in Escherichia coli pneumonia in C57BL/6 mice was associated with high levels of leukotriene (LT) B4 in the injured alveolus. More importantly, the antimicrobial effect of MSC EV was abrogated by cotreatment with a LTB4 BLT1 antagonist. To determine the role of MSC EV on LT metabolism, we measured the effect of MSC EV on a known ATP-binding cassette transporter, multidrug resistance-associated protein 1 (MRP1), and found that MSC EV suppressed MRP1 mRNA, protein, and pump function in LPS-stimulated Raw264.7 cells in vitro. The synthesis of LTB4 and LTC4 from LTA4 are competitive, and MRP1 is the efflux pump for LTC4 Inhibition of MRP1 will increase LTB4 production. In addition, administration of a nonspecific MRP1 inhibitor (MK-571) reduced LTC4 and subsequently increased LTB4 levels in C57BL/6 mice with acute lung injury, increasing overall antimicrobial activity. We previously found that the biological effects of MSC EV were through the transfer of its content, such as mRNA, microRNA, and proteins, to target cells. In the current study, miR-145 knockdown abolished the effect of MSC EV on the inhibition of MRP1 in vitro and the antimicrobial effect in vivo. In summary, MSC EV suppressed MRP1 activity through transfer of miR-145, thereby resulting in enhanced LTB4 production and antimicrobial activity through LTB4/BLT1 signaling.

Dual inhibition of complement factor 5 and leukotriene B4 synergistically suppresses murine pemphigoid disease.

The treatment of most autoimmune diseases still relies on systemic immunosuppression and is associated with severe side effects. The development of drugs that more specifically abrogate pathogenic pathways is therefore most desirable. In nature, such specificity is exemplified, e.g., by the soft tick-derived biotherapeutic Coversin, which locally suppresses immune responses by inhibiting complement factor 5 (C5) and leukotriene B4 (LTB4). C5a, a proteolytic fragment of C5, and LTB4 are critical drivers of skin inflammation in pemphigoid diseases (PDs), a group of autoimmune blistering skin diseases. Here, we demonstrate that both Coversin and its mutated form L-Coversin, which inhibits LTB4 only, dose dependently attenuate disease in a model of bullous pemphigoid-like epidermolysis bullosa acquisita (BP-like EBA). Coversin, however, reduces disease more effectively than L-Coversin, indicating that inhibition of C5 and LTB4 synergize in their suppressing effects in this model. Further supporting the therapeutic potential of Coversin in humans, we found that C5a and LTB4 are both present in the blister fluid of patients with BP in quantities inducing the recruitment of granulocytes and that the number of cells expressing their receptors, C5aR1 and BLT1, respectively, is increased in perilesional skin. Collectively, our results highlight Coversin and possibly L-Coversin as potential therapeutics for PDs.

Resolvin E3 attenuates allergic airway inflammation via the interleukin-23-interleukin-17A pathway.

We investigated the effects of resolvin E (RvE) 1, RvE2, and RvE3 on IL-4- and IL-33-stimulated bone marrow-derived dendritic cells (BMDCs) from house dust mite (HDM)-sensitized mice. We also investigated the role of RvE3 in a murine model of HDM-induced airway inflammation. In vitro, BMDCs from HDM-sensitized mice were stimulated with IL-4 and IL-33 and then treated with RvE1, RvE2, RvE3, or vehicle. RvE1, RvE2, and RvE3 suppressed IL-23 release from BMDCs. In vivo, RvE3 administrated to HDM-sensitized and challenged mice in the resolution phase promoted a decline in total numbers of inflammatory cells and eosinophils, reduced levels of IL-23 and IL-17 in lavage fluid, and suppressed IL-23 and IL-17A mRNA expression in lung and peribronchial lymph nodes. RvE3 also reduced resistance in the lungs of HDM-sensitized mice. A NanoBiT ß-arrestin recruitment assay using human embryonic kidney 293 cells revealed that pretreatment with RvE3 suppressed the leukotriene B4 (LTB4)-induced ß-arrestin 2 binding to LTB4 receptor 1 (BLT1R), indicating that RvE3 antagonistically interacts with BLT1R. Collectively, these findings indicate that RvE3 facilitates the resolution of allergic airway inflammation, partly by regulating BLT1R activity and selective cytokine release by dendritic cells. Our results accordingly identify RvE3 as a potential therapeutic target for the management of asthma.-Sato, M., Aoki-Saito, H., Fukuda, H., Ikeda, H., Koga, Y., Yatomi, M., Tsurumaki, H., Maeno, T., Saito, T., Nakakura, T., Mori, T., Yanagawa, M., Abe, M., Sako, Y., Dobashi, K., Ishizuka, T., Yamada, M., Shuto, S., Hisada, T. Resolvin E3 attenuates allergic airway inflammation via the interleukin-23-interleukin-17A pathway.

Non-canonical NLRP3 inflammasome activation and IL-1ß signaling are necessary to L. amazonensis control mediated by P2X7 receptor and leukotriene B4.

Leishmaniasis is a neglected tropical disease affecting millions of individuals worldwide. P2X7 receptor has been linked to the elimination of Leishmania amazonensis. Biological responses evoked by P2X7 receptor activation have been well-documented, including apoptosis, phagocytosis, cytokine release, such as IL-1ß. It was demonstrated that NLRP3 inflammasome activation and IL-1ß signaling participated in resistance against L. amazonensis. Furthermore, our group has shown that L. amazonensis elimination through P2X7 receptor activation depended on leukotriene B4 (LTB4) production and release. Therefore, we investigated whether L. amazonensis elimination by P2X7 receptor and LTB4 involved NLRP3 inflammasome activation and IL-1ß signaling. We showed that macrophages from NLRP3-/-, ASC-/-, Casp-1/11-/-, gp91phox-/- , and IL-1R-/- mice treated with ATP or LTB4 did not decrease parasitic load as was observed in WT mice. When ASC-/- macrophages were treated with exogenous IL-1ß, parasite killing was noted, however, we did not see parasitic load reduction in IL-1R-/- macrophages. Similarly, macrophages from P2X7 receptor-deficient mice treated with IL-1ß also showed decreased parasitic load. In addition, when we infected Casp-11-/- macrophages, neither ATP nor LTB4 were able to reduce parasitic load, and Casp-11-/- mice were more susceptible to L. amazonensis infection than were WT mice. Furthermore, P2X7-/- L. amazonensis-infected mice locally treated with exogenous LTB4 showed resistance to infection, characterized by lower parasite load and smaller lesions compared to untreated P2X7-/- mice. A similar observation was noted when infected P2X7-/- mice were treated with IL-1ß, i.e., lower parasite load and smaller lesions compared to P2X7-/- mice. These data suggested that L. amazonensis elimination mediated by P2X7 receptor and LTB4 was dependent on non-canonical NLRP3 inflammasome activation, ROS production, and IL-1ß signaling.

Gliotoxin from Aspergillus fumigatus Abrogates Leukotriene B4 Formation through Inhibition of Leukotriene A4 Hydrolase.

The epidithiodioxopiperazine gliotoxin is a virulence factor of Aspergillus fumigatus, the most important airborne fungal pathogen of humans. Gliotoxin suppresses innate immunity in invasive aspergillosis, particularly by compromising neutrophils, but the underlying molecular mechanisms remain elusive. Neutrophils are the first responders among innate immune cells recruited to sites of infection by the chemoattractant leukotriene (LT)B4 that is biosynthesized by 5-lipoxygenase and LTA4 hydrolase (LTA4H). Here, we identified gliotoxin as inhibitor of LTA4H that selectively abrogates LTB4 formation in human leukocytes and in distinct animal models. Gliotoxin failed to inhibit the formation of other eicosanoids and the aminopeptidase activity of the bifunctional LTA4H. Suppression of LTB4 formation by gliotoxin required the cellular environment and/or reducing conditions, and only the reduced form of gliotoxin inhibited LTA4H activity. Conclusively, gliotoxin suppresses the biosynthesis of the potent neutrophil chemoattractant LTB4 by direct interference with LTA4H thereby impairing neutrophil functions in invasive aspergillosis.

20-Hydroxy- and 20-carboxy-leukotriene (LT) B4 downregulate LTB4 -mediated responses of human neutrophils and eosinophils.

Leukotriene B4 (LTB4 ) plays a prominent role in innate immunity as it induces phagocyte recruitment, the release of antimicrobial effectors, and as it potentiates the ingestion and killing of pathogens. In humans, LTB4 has a short half-life and is rapidly metabolized by leukocytes, notably into 20-OH- and 20-COOH-LTB4 by neutrophils. Although these LTB4 metabolites bind to the BLT1 receptor with high affinity, they activate neutrophils to a much lower extent than LTB4 . We thus postulated that LTB4 metabolites could dampen BLT1 -mediated responses, therefore limiting the impact of LTB4 on human neutrophil functions. We found that 20-OH-LTB4 and 20-COOH-LTB4 inhibited all of the LTB4 -mediated neutrophil responses we tested (migration, degranulation, leukotriene biosynthesis). The potencies of the different compounds at inhibiting LTB4 -mediated responses were 20-OH-LTB4  = CP 105,696 (BLT1 antagonist) > > 20-COOH-LTB4 ≥ resolvin E1 (RVE1 ). In contrast, the fMLP- and IL-8-mediated responses we tested were not affected by the LTB4 metabolites or RVE1 . 20-OH-LTB4 and 20-COOH-LTB4 also inhibited the LTB4 -mediated migration of human eosinophils but not that induced by 5-KETE. Moreover, using 20-COOH-LTB4 , LTB4 , and LTB4 -alkyne, we show that LTB4 is a chemotactic, rather than a chemokinetic factor for both human neutrophils and eosinophils. In conclusion, our data indicate that LTB4 metabolites and RVE1 act as natural inhibitors of LTB4 -mediated responses. Thus, preventing LTB4 ω-oxidation might result in increased innate immunity and granulocyte functions.

A noncanonical role for the engulfment gene ELMO1 in neutrophils that promotes inflammatory arthritis.

Rheumatoid arthritis is characterized by progressive joint inflammation and affects ~1% of the human population. We noted single-nucleotide polymorphisms (SNPs) in the apoptotic cell-engulfment genes ELMO1, DOCK2, and RAC1 linked to rheumatoid arthritis. As ELMO1 promotes cytoskeletal reorganization during engulfment, we hypothesized that ELMO1 loss would worsen inflammatory arthritis. Surprisingly, Elmo1-deficient mice showed reduced joint inflammation in acute and chronic arthritis models. Genetic and cell-biology studies revealed that ELMO1 associates with receptors linked to neutrophil function in arthritis and regulates activation and early neutrophil recruitment to the joints, without general inhibition of inflammatory responses. Further, neutrophils from the peripheral blood of human donors that carry the SNP in ELMO1 associated with arthritis display increased migratory capacity, whereas ELMO1 knockdown reduces human neutrophil migration to chemokines linked to arthritis. These data identify 'noncanonical' roles for ELMO1 as an important cytoplasmic regulator of specific neutrophil receptors and promoter of arthritis.

Excessive localized leukotriene B4 levels dictate poor skin host defense in diabetic mice.

Poorly controlled diabetes leads to comorbidities and enhanced susceptibility to infections. While the immune components involved in wound healing in diabetes have been studied, the components involved in susceptibility to skin infections remain unclear. Here, we examined the effects of the inflammatory lipid mediator leukotriene B4 (LTB4) signaling through its receptor B leukotriene receptor 1 (BLT1) in the progression of methicillin-resistant Staphylococcus aureus (MRSA) skin infection in 2 models of diabetes. Diabetic mice produced higher levels of LTB4 in the skin, which correlated with larger nonhealing lesion areas and increased bacterial loads compared with nondiabetic mice. High LTB4 levels were also associated with dysregulated cytokine and chemokine production, excessive neutrophil migration but impaired abscess formation, and uncontrolled collagen deposition. Both genetic deletion and topical pharmacological BLT1 antagonism restored inflammatory response and abscess formation, followed by a reduction in the bacterial load and lesion area in the diabetic mice. Macrophage depletion in diabetic mice limited LTB4 production and improved abscess architecture and skin host defense. These data demonstrate that exaggerated LTB4/BLT1 responses mediate a derailed inflammatory milieu that underlies poor host defense in diabetes. Prevention of LTB4 production/actions could provide a new therapeutic strategy to restore host defense in diabetes.

EMPIRE-CF: A phase II randomized placebo-controlled trial of once-daily, oral acebilustat in adult patients with cystic fibrosis - Study design and patient demographics.

Inflammation causes irreparable damage in the cystic fibrosis (CF) lung. Despite high standards of care and the advent of new therapies, inflammation continues to cause significant loss of lung function and morbidity. Acebilustat is a once-daily, oral molecule with anti-inflammatory activity through the inhibition of LTA4 hydrolase and modulation of LTB4. It has potential to reduce lung function decline and pulmonary exacerbations in patients with CF and is currently being tested in a Phase II multicenter, randomized, double-blind, placebo-controlled, parallel-group study (EMPIRE-CF). Strict inclusion criteria based on modeling of the Cystic Fibrosis Foundation Patient Registry data were selected to enrich the trial with patients most likely to benefit from chronic anti-inflammatory therapy that reduces lung function decline. 200 patients between 18 and 30 years of age, with an FEV1 percent predicted (pp) ≥50%, and ≥1 exacerbation in the past year have been enrolled. Patients are randomized 1:1:1 to placebo, acebilustat 50 mg or 100 mg for 48 weeks, taken concomitantly with their current standard of care, and stratified based on concomitant CFTR modulator use, baseline FEV1pp (50% to 75% and >75%), and number of exacerbations in the past year (1 or >1). The primary endpoints are absolute change from baseline in FEV1pp and safety outcomes. Secondary endpoints include rate of pulmonary exacerbations and time to first pulmonary exacerbation. Biomarkers of inflammation will also be assessed. EMPIRE-CF is expected to identify the optimal patient population, dose, duration and endpoints for future acebilustat trials, and widen understanding of the drug's efficacy in patients with CF.

Mast Cell-Dependent CD8+ T-cell Recruitment Mediates Immune Surveillance of Intestinal Tumors in ApcMin/+ Mice.

The presence of mast cells in some human colorectal cancers is a positive prognostic factor, but the basis for this association is incompletely understood. Here, we found that mice with a heterozygous mutation in the adenomatous polyposis coli gene (ApcMin/+) displayed reduced intestinal tumor burdens and increased survival in a chemokine decoy receptor, ACKR2-null background, which led to discovery of a critical role for mast cells in tumor defense. ACKR2-/-ApcMin/+ tumors showed increased infiltration of mast cells, their survival advantage was lost in mast cell-deficient ACKR2-/-SA-/-ApcMin/+ mice as the tumors grew rapidly, and adoptive transfer of mast cells restored control of tumor growth. Mast cells from ACKR2-/- mice showed elevated CCR2 and CCR5 expression and were also efficient in antigen presentation and activation of CD8+ T cells. Mast cell-derived leukotriene B4 (LTB4) was found to be required for CD8+ T lymphocyte recruitment, as mice lacking the LTB4 receptor (ACKR2-/-BLT1-/-ApcMin/+) were highly susceptible to intestinal tumor-induced mortality. Taken together, these data demonstrate that chemokine-mediated recruitment of mast cells is essential for initiating LTB4/BLT1-regulated CD8+ T-cell homing and generation of effective antitumor immunity against intestinal tumors. We speculate that the pathway reported here underlies the positive prognostic significance of mast cells in selected human tumors. Cancer Immunol Res; 6(3); 332-47. ©2018 AACR.

Leukotriene B4-Mediated Neutrophil Recruitment Causes Pulmonary Capillaritis during Lethal Fungal Sepsis.

Candida albicans bloodstream infection causes fungal septicaemia and death in over half of afflicted patients. Polymorphonuclear leukocytes (PMN) mediate defense against invasive candidiasis, but their role in protection versus tissue injury and sepsis is unclear. We observe PMN intravascular swarming and subsequent clustering in response to C. albicans yeast in a lethal septic mouse and human pulmonary circulation model. Live C. albicans sequester to the endothelium and are immediately captured by complement-dependent PMN chemotaxis, which is required for host survival. However, complement activation also leads to Leukotriene B4 (LTB4)-mediated intravascular PMN clustering and occlusion, resulting in capillaritis with pulmonary hemorrhage and hypoxemia. This clustering is unique to fungi and triggered by fungal cell wall components. PMN clustering is absent in mice lacking LTB4-receptor, and capillaritis is attenuated upon pharmacological LTB4 blockade without affecting phagocytosis. Therefore, therapeutically disrupting infection-induced capillaritis may limit organ injury without impairing host defense during fungal sepsis.