Enteric helminth coinfection enhances host susceptibility to neurotropic flaviviruses via a tuft cell-IL-4 receptor signaling axis.

Although enteric helminth infections modulate immunity to mucosal pathogens, their effects on systemic microbes remain less established. Here, we observe increased mortality in mice coinfected with the enteric helminth Heligmosomoides polygyrus bakeri (Hpb) and West Nile virus (WNV). This enhanced susceptibility is associated with altered gut morphology and transit, translocation of commensal bacteria, impaired WNV-specific T cell responses, and increased virus infection in the gastrointestinal tract and central nervous system. These outcomes were due to type 2 immune skewing, because coinfection in Stat6-/- mice rescues mortality, treatment of helminth-free WNV-infected mice with interleukin (IL)-4 mirrors coinfection, and IL-4 receptor signaling in intestinal epithelial cells mediates the susceptibility phenotypes. Moreover, tuft cell-deficient mice show improved outcomes with coinfection, whereas treatment of helminth-free mice with tuft cell-derived cytokine IL-25 or ligand succinate worsens WNV disease. Thus, helminth activation of tuft cell-IL-4-receptor circuits in the gut exacerbates infection and disease of a neurotropic flavivirus.

Interleukin-33 Induces the Enzyme Tryptophan Hydroxylase 1 to Promote Inflammatory Group 2 Innate Lymphoid Cell-Mediated Immunity.

Group 2 innate lymphoid cells (ILC2s) regulate immunity, inflammation, and tissue homeostasis. Two distinct subsets of ILC2s have been described: steady-state natural ILC2s and inflammatory ILC2s, which are elicited following helminth infection. However, how tissue-specific cues regulate these two subsets of ILC2s and their effector functions remains elusive. Here, we report that interleukin-33 (IL-33) promotes the generation of inflammatory ILC2s (ILC2INFLAM) via induction of the enzyme tryptophan hydroxylase 1 (Tph1). Tph1 expression was upregulated in ILC2s upon activation with IL-33 or following helminth infection in an IL-33-dependent manner. Conditional deletion of Tph1 in lymphocytes resulted in selective impairment of ILC2INFLAM responses and increased susceptibility to helminth infection. Further, RNA sequencing analysis revealed altered gene expression in Tph1 deficient ILC2s including inducible T cell co-stimulator (Icos). Collectively, these data reveal a previously unrecognized function for IL-33, Tph1, and ICOS in promoting inflammatory ILC2 responses and type 2 immunity at mucosal barriers.

Regulation of intestinal immunity and tissue repair by enteric glia.

Tissue maintenance and repair depend on the integrated activity of multiple cell types1. Whereas the contributions of epithelial2,3, immune4,5 and stromal cells6,7 in intestinal tissue integrity are well understood, the role of intrinsic neuroglia networks remains largely unknown. Here we uncover important roles of enteric glial cells (EGCs) in intestinal homeostasis, immunity and tissue repair. We demonstrate that infection of mice with Heligmosomoides polygyrus leads to enteric gliosis and the upregulation of an interferon gamma (IFNγ) gene signature. IFNγ-dependent gene modules were also induced in EGCs from patients with inflammatory bowel disease8. Single-cell transcriptomics analysis of the tunica muscularis showed that glia-specific abrogation of IFNγ signalling leads to tissue-wide activation of pro-inflammatory transcriptional programs. Furthermore, disruption of the IFNγ-EGC signalling axis enhanced the inflammatory and granulomatous response of the tunica muscularis to helminths. Mechanistically, we show that the upregulation of Cxcl10 is an early immediate response of EGCs to IFNγ signalling and provide evidence that this chemokine and the downstream amplification of IFNγ signalling in the tunica muscularis are required for a measured inflammatory response to helminths and resolution of the granulomatous pathology. Our study demonstrates that IFNγ signalling in enteric glia is central to intestinal homeostasis and reveals critical roles of the IFNγ-EGC-CXCL10 axis in immune response and tissue repair after infectious challenge.

TNF-α Triggers RIP1/FADD/Caspase-8-Mediated Apoptosis of Astrocytes and RIP3/MLKL-Mediated Necroptosis of Neurons Induced by Angiostrongylus cantonensis Infection.

Angiostrongylus cantonensis (AC) can cause severe eosinophilic meningitis or encephalitis in non-permissive hosts accompanied by apoptosis and necroptosis of brain cells. However, the explicit underlying molecular basis of apoptosis and necroptosis upon AC infection has not yet been elucidated. To determine the specific pathways of apoptosis and necroptosis upon AC infection, gene set enrichment analysis (GSEA) and protein-protein interaction (PPI) analysis for gene expression microarray (accession number: GSE159486) of mouse brain infected by AC revealed that TNF-α likely played a central role in the apoptosis and necroptosis in the context of AC infection, which was further confirmed via an in vivo rescue assay after treating with TNF-α inhibitor. The signalling axes involved in apoptosis and necroptosis were investigated via immunoprecipitation and immunoblotting. Immunofluorescence was used to identify the specific cells that underwent apoptosis or necroptosis. The results showed that TNF-α induced apoptosis of astrocytes through the RIP1/FADD/Caspase-8 axis and induced necroptosis of neurons by the RIP3/MLKL signalling pathway. In addition, in vitro assay revealed that TNF-α secretion by microglia increased upon LSA stimulation and caused necroptosis of neurons. The present study provided the first evidence that TNF-α was secreted by microglia stimulated by AC infection, which caused cell death via parallel pathways of astrocyte apoptosis (mediated by the RIP1/FADD/caspase-8 axis) and neuron necroptosis (driven by the RIP3/MLKL complex). Our research comprehensively elucidated the mechanism of cell death after AC infection and provided new insight into targeting TNF-α signalling as a therapeutic strategy for CNS injury.

Th9 Cells Drive Host Immunity against Gastrointestinal Worm Infection.

Type 2 inflammatory cytokines, including interleukin-4 (IL-4), IL-5, IL-9, and IL-13, drive the characteristic features of immunity against parasitic worms and allergens. Whether IL-9 serves an essential role in the initiation of host-protective responses is controversial, and the importance of IL-9- versus IL-4-producing CD4⁺ effector T cells in type 2 immunity is incompletely defined. Herein, we generated IL-9-deficient and IL-9-fluorescent reporter mice that demonstrated an essential role for this cytokine in the early type 2 immunity against Nippostrongylus brasiliensis. Whereas T helper 9 (Th9) cells and type 2 innate lymphoid cells (ILC2s) were major sources of infection-induced IL-9 production, the adoptive transfer of Th9 cells, but not Th2 cells, caused rapid worm expulsion, marked basophilia, and increased mast cell numbers in Rag2-deficient hosts. Taken together, our data show a critical and nonredundant role for Th9 cells and IL-9 in host-protective type 2 immunity against parasitic worm infection.

Control of T helper 2 responses by transcription factor IRF4-dependent dendritic cells.

CD4⁺ T cell differentiation is regulated by specialized antigen-presenting cells. Dendritic cells (DCs) produce cytokines that promote naive CD4⁺ T cell differentiation into T helper 1 (Th1), Th17, and inducible T regulatory (iTreg) cells. However, the initiation of Th2 cell responses remains poorly understood, although it is likely that more than one mechanism might be involved. Here we have defined a specific DC subset that is involved in Th2 cell differentiation in vivo in response to a protease allergen, as well as infection with Nippostrongylus brasiliensis. We have demonstrated that this subset is controlled by the transcription factor interferon regulatory factor 4 (IRF4), which is required for their differentiation and Th2 cell-inducing function. IRF4 is known to control Th2 cell differentiation and Th2 cell-associated suppressing function in Treg cells. Our finding suggests that IRF4 also plays a role in DCs where it controls the initiation of Th2 cell responses.

CD301b⁺ dermal dendritic cells drive T helper 2 cell-mediated immunity.

Unlike other types of T helper (Th) responses, whether the development of Th2 cells requires instruction from particular subset of dendritic cells (DCs) remains unclear. By using an in vivo depletion approach, we have shown that DCs expressing CD301b were required for the generation of Th2 cells after subcutaneous immunization with ovalbumin (OVA) along with papain or alum. CD301b⁺ DCs are distinct from epidermal or CD207⁺ dermal DCs (DDCs) and were responsible for transporting antigen injected subcutaneously with Th2-type adjuvants. Transient depletion of CD301b⁺ DCs resulted in less effective accumulation and decreased expression of CD69 by polyclonal CD4⁺ T cells in the lymph node. Moreover, despite intact cell division and interferon-γ production, CD301b⁺ DC depletion led to blunted interleukin-4 production by OVA-specific OT-II transgenic CD4⁺ T cells and significantly impaired Th2 cell development upon infection with Nippostrongylus brasiliensis. These results reveal CD301b⁺ DDCs as the key mediators of Th2 immunity.

The Prostaglandin D2 Receptor CRTH2 Promotes IL-33-Induced ILC2 Accumulation in the Lung.

Group 2 innate lymphoid cells (ILC2s) are rare innate immune cells that accumulate in tissues during allergy and helminth infection, performing critical effector functions that drive type 2 inflammation. ILC2s express ST2, the receptor for the cytokine IL-33, and chemoattractant receptor-homologous molecule expressed on Th2 cells (CRTH2), a receptor for the bioactive lipid prostaglandin D2 (PGD2). The IL-33-ST2 and the PGD2-CRTH2 pathways have both been implicated in promoting ILC2 accumulation during type 2 inflammation. However, whether these two pathways coordinate to regulate ILC2 population size in the tissue in vivo remains undefined. In this study, we show that ILC2 accumulation in the murine lung in response to systemic IL-33 treatment was partially dependent on CRTH2. This effect was not a result of reduced ILC2 proliferation, increased apoptosis or cell death, or differences in expression of the ST2 receptor in the absence of CRTH2. Rather, data from adoptive transfer studies suggested that defective accumulation of CRTH2-deficient ILC2s in response to IL-33 was due to altered ILC2 migration patterns. Whereas donor wild-type ILC2s preferentially accumulated in the lungs compared with CRTH2-deficient ILC2s following transfer into IL-33-treated recipients, wild-type and CRTH2-deficient ILC2s accumulated equally in the recipient mediastinal lymph node. These data suggest that CRTH2-dependent effects lie downstream of IL-33, directly affecting the migration of ILC2s into inflamed lung tissues. A better understanding of the complex interactions between the IL-33 and PGD2-CRTH2 pathways that regulate ILC2 population size will be useful in understanding how these pathways could be targeted to treat diseases associated with type 2 inflammation.

Heligmosomoides polygyrus bakeri Infection Decreases Smad7 Expression in Intestinal CD4+ T Cells, Which Allows TGF-ß to Induce IL-10-Producing Regulatory T Cells That Block Colitis.

Helminthic infections modulate host immunity and may protect their hosts from developing immunological diseases like inflammatory bowel disease. Induction of regulatory T cells (Tregs) may be an important part of this protective process. Heligmosomoides polygyrus bakeri infection also promotes the production of the regulatory cytokines TGF-ß and IL-10 in the gut. In the intestines, TGF-ß helps induce regulatory T cells. This study used Foxp3/IL-10 double reporter mice to investigate the effect of TGF-ß on the differentiation of colon and mesenteric lymph node-derived murine Foxp3- IL-10- CD4+ T cells into their regulatory phenotypes. Foxp3- IL-10- CD4+ T cells from H. polygyrus bakeri-infected mice, as opposed to T cells from uninfected animals, cultured in vitro with TGF-ß and anti-CD3/CD28 mAb differentiated into Foxp3+ and/or IL-10+ T cells. The IL-10-producing T cells nearly all displayed CD25. Smad7 is a natural inhibitor of TGF-ß signaling. In contrast to gut T cells from uninfected mice, Foxp3- IL10- CD4+ T cells from H. polygyrus bakeri-infected mice displayed reduced Smad7 expression and responded to TGF-ß with Smad2/3 phosphorylation. The TGF-ß-induced Tregs that express IL-10 blocked colitis when transferred into the Rag/CD25- CD4+ T cell transfer model of inflammatory bowel disease. TGF-ß had a greatly diminished capacity to induce Tregs in H. polygyrus bakeri-infected transgenic mice with constitutively high T cell-specific Smad7 expression. Thus, infection with H. polygyrus bakeri causes down-modulation in Smad7 expression in intestinal CD4+ T cells, which allows the TGF-ß produced in response to the infection to induce the Tregs that prevent colitis.

Inflammasome-Independent Role for NLRP3 in Controlling Innate Antihelminth Immunity and Tissue Repair in the Lung.

Alternatively activated macrophages are essential effector cells during type 2 immunity and tissue repair following helminth infections. We previously showed that Ym1, an alternative activation marker, can drive innate IL-1R-dependent neutrophil recruitment during infection with the lung-migrating nematode, Nippostrongylus brasiliensis, suggesting a potential role for the inflammasome in the IL-1-mediated innate response to infection. Although inflammasome proteins such as NLRP3 have important proinflammatory functions in macrophages, their role during type 2 responses and repair are less defined. We therefore infected Nlrp3 -/- mice with N. brasiliensis Unexpectedly, compared with wild-type (WT) mice, infected Nlrp3 -/- mice had increased neutrophilia and eosinophilia, correlating with enhanced worm killing but at the expense of increased tissue damage and delayed lung repair. Transcriptional profiling showed that infected Nlrp3 -/- mice exhibited elevated type 2 gene expression compared with WT mice. Notably, inflammasome activation was not evident early postinfection with N. brasiliensis, and in contrast to Nlrp3 -/- mice, antihelminth responses were unaffected in caspase-1/11-deficient or WT mice treated with the NLRP3-specific inhibitor MCC950. Together these data suggest that NLRP3 has a role in constraining lung neutrophilia, helminth killing, and type 2 immune responses in an inflammasome-independent manner.

Pathology of Angiostrongylus cantonensis infection in two model avian hosts.

Angiostrongylus cantonensis causes severe neurological disorders in a wide range of warm-blooded animals, including several avian species. A laboratory isolate of A. cantonensis originating from French Polynesia, genotyped as clade 2, was used to assess the effect of experimental infection in chicken and Japanese quail. Low dose groups of birds were infected orally by 100 L3 larvae, high dose groups by 1500 L3 larvae and the birds in the third group were fed three infected snails, mimicking a natural infection. Clinical signs during the first week after infection, haematology, biochemistry, gross lesions and histology findings were used to assess the pathology of the infection. Some of the infected birds showed peripheral eosinophilia, while mild neurological signs were seen in others. No larvae were observed in serial sections of the central nervous system of infected birds 1 week after infection and no major gross lesions were observed during necropsy; histopathology did not reveal lesions directly attributable to A. cantonensis infection. Our results suggest that galliform birds are not highly susceptible to A. cantonensis infection and open a question of the importance of Galliformes in endemic areas as natural pest control, lowering the number of hosts carrying the infective larvae.

Gross, microscopic, radiologic, echocardiographic and haematological findings in rats experimentally infected with Angiostrongylus cantonensis.

Although the gross and microscopic pathology in rats infected with Angiostrongylus cantonensis has been well described, corresponding changes detected using diagnostic imaging modalities have not been reported. This work describes the cardiopulmonary changes in mature Wistar rats chronically infected with moderate burdens of A. cantonensis using radiology, computed tomography (CT), CT angiography, echocardiography, necropsy and histological examinations. Haematology and coagulation studies were also performed. Thoracic radiography, CT and CT angiography showed moderately severe alveolar pulmonary patterns mainly affecting caudal portions of the caudal lung lobes and associated dilatation of the caudal lobar pulmonary arteries. Presumptive worm profiles could be detected using echocardiography, with worms seen in the right ventricular outflow tract or straddling either the pulmonary and/or the tricuspid valves. Extensive, multifocal, coalescing dark areas and multiple pale foci affecting the caudal lung lobes were observed at necropsy. Histologically, these were composed of numerous large, confluent granulomas and fibrotic nodules. Adult worms were found predominantly in the mid- to distal pulmonary arteries. An inflammatory leukogram, hyperproteinaemia and hyperfibrinogenaemia were found in most rats. These findings provide a comparative model for A. cantonensis in its accidental hosts, such as humans and dogs. In addition, the pathological and imaging changes are comparable to those seen in dogs infected with Angiostrongylus vasorum, suggesting rats infected with A. cantonensis could be a model for dogs with A. vasorum infection.

Chronic neuroangiostrongyliasis: case study of chronic presentations in Hawaii.

This paper describes chronic features of neuroangiostrongyliasis (NAS), a long-term outcome of the disease that has not been adequately described. Current and past literature is predominantly limited to acute manifestations of NAS, and mention of chronic, ongoing clinical symptoms is usually limited to brief notes in a discussion of severe cases. This study investigated the long-term outcomes in ten individuals who were diagnosed with acute neuroangiostrongyliasis in Hawaii between 2009 and 2017. The study demonstrates a significant number of persons in Hawaii sustain residual symptoms for many years, including troublesome sensory paresthesia (abnormal spontaneous sensations of skin experienced as 'burning, pricking, pins and needles'; also described as allodynia or hyperesthesia) and extremity muscle pains. As a consequence, employment and economic hardships, domestic relocations, and psychological impairments affecting personal relationships occurred. The study summarizes common features of chronic disease, sensory paresthesia and hyperesthesia, diffuse muscular pain, insomnia, and accompanying emotional distress; highlights the frequently unsuccessful endeavours of individuals struggling to find effective treatment; proposes pathogenic mechanisms responsible for prolonged illness including possible reasons for differences in disease presentation in Hawaii compared to Southeast Asia.

Angiostrongyliasis infection masquerading as granulomatosis with polyangiitis: a case-based review.

Pulmonary angiitis is a small vessel vasculitis commonly reported in granulomatosis with polyangiitis (GPA) but is rarely attributed to angiostrongyliasis. We report a case of a patient with well-controlled rheumatoid arthritis, who was treated for GPA based on lung biopsy results with glucocorticoids (GC). Upon re-review of the initial pathology, along with peripheral eosinophilia and history of recent travel, the patient was eventually diagnosed with angiostrongylus-like nematode infection. GCs were subsequently discontinued and instead, the patient was treated with anthelmintics with complete resolution of symptoms. Commonly associated with eosinophilic meningitis or abdominal angiostrongyliasis in humans, clinical pulmonary manifestations of this parasite species are rare. With parasitic infiltration of the pulmonary vessels mimicking clinical GPA, diagnosis and treatment can be difficult in these patients. We discuss the third-reported case and first-reported survivor of Angiostrongylus-induced pulmonary angiitis followed by a focused review of the literature.

Angiostrongylus cantonensis infection induces MMP-9 and causes tight junction protein disruption associated with Purkinje cell degeneration.

Angiostrongylus cantonensis causes a human central nervous system (CNS) infection characterized by eosinophilic meningitis or meningoencephalitis. Individuals infected with A. cantonensis exhibit unbalanced walking. The mechanism of extensive neurological impairments of hosts caused by A. cantonensis larvae remains unclear. Tight junction proteins (e.g., claudin-5 and zonula occludens-1) are the most important regulators of paracellular permeability and cellular adhesion. In a previous study, we found that increased matrix metalloproteinase-9 (MMP-9) activity may be associated with blood-CNS barrier disruption and/or the degeneration of Purkinje cells in eosinophilic meningitis caused by A. cantonensis. In the present study, the co-localization of MMP-9 and tight junction proteins on the degeneration of Purkinje cells was measured via confocal laser scanning immunofluorescence microscopy. The statistical evidence indicated that MMP-9 correlated between tight junction protein disruption and Purkinje cell degeneration at 20 days post-infection with A. cantonensis. In conclusion, Purkinje cell degeneration is highly correlated with tight junction protein disruption via the MMP-9 activation pathway.

Troglostrongylus brevior is the dominant lungworm infecting feral cats in Jerusalem.

Feline lungworms infect the respiratory tract of wild and domestic cats, causing infection often associated with clinical disease. Until recently, Aelurostrongylus abstrusus has been considered the most relevant species of lungworm, while Troglostrongylus brevior was considered of less significance. Fecal samples of feral cats from Jerusalem, Israel, collected over a year, were examined for first stage lungworm larvae (L1) using the Baermann method. Positive samples were morphologically identified, and their species identity was molecularly confirmed. Forty of 400 (10.0%) cats were lungworm-positive, of which 38/40 (95.0%) shed Troglostrongylus brevior and 6/40 (15.0%) shed Aelurostrongylus abstrusus. Four cats (10.0%) had mixed infections with both lungworm species. L1 shedding was associated with clinical respiratory signs in 11 (19.0%) T. brevior shedding cats of a total of 58 cats manifesting respiratory signs, while 23/342 (6.7%) cats without respiratory signs were L1-positive (p = 0.006). Non-respiratory clinical signs were also found to be more prevalent in L1 shedders (p = 0.012). A young kitten ≤ 4 weeks of age shed T. brevior L1 larvae. DNA sequences of both lungworm species using the ribosomal internal transcribed spacer 2 (ITS2) locus were > 99% similar to other sequences deposited in GenBank, suggesting that T. brevior and A. abstrusus ITS2 sequences are both highly conserved. In conclusion, L1 shedding in feral cats from Jerusalem were mostly caused by T. brevior with only a small proportion involving A. abstrusus, different from many studies from other geographical regions.

Trefoil Factor 2 Promotes Type 2 Immunity and Lung Repair through Intrinsic Roles in Hematopoietic and Nonhematopoietic Cells.

Trefoil factors (TFFs) are small secreted proteins that regulate tissue integrity and repair at mucosal surfaces, particularly in the gastrointestinal tract. However, their relative contribution(s) to controlling baseline lung function or the extent of infection-induced lung injury are unknown issues. With the use of irradiation bone marrow chimeras, we found that TFF2 produced from both hematopoietic- and nonhematopoietic-derived cells is essential for host protection, proliferation of alveolar type 2 cells, and restoration of pulmonary gas exchange after infection with the hookworm parasite Nippostrongylus brasiliensis. In the absence of TFF2, lung epithelia were unable to proliferate and expressed reduced lung mRNA transcript levels for type 2 response-inducing IL-25 and IL-33 after infectious injury. Strikingly, even in the absence of infection or irradiation, TFF2 deficiency compromised lung structure and function, as characterized by distended alveoli and reduced blood oxygen levels relative to wild-type control mice. Taken together, we show a previously unappreciated role for TFF2, produced by either hematopoietic or nonhematopoietic sources, as a pro-proliferative factor for lung epithelial cells under steady-state and infectious injury conditions.

Nippostrongylus brasiliensis infection inhibits hippocampal neurogenesis in mice.

The brain has long been considered a site of "immune privilege"; however, recent evidence indicates the presence of brain-immune interactions in physiological and pathological conditions. Neurogenesis, a process of generating functionally integrated neurons, occurs in the adult brain of mammals. The adult neurogenesis predominantly takes place in the subgranular zone (SGZ) of the hippocampal dentate gyrus and the subventricular zone (SVZ). Several studies have shown that an immune reaction or alteration could affect adult neurogenesis activity, suggesting a link between the immune system and adult neurogenesis. Helminth infection is one of the activators of Th2 immune response. However, the influence of this type of immune reaction on adult neurogenesis is not well studied. In this study, we evaluated adult neurogenesis in mice infected with the helminth Nippostrongylus brasiliensis (Nb). Immunohistochemically, the number of both doublecortin-positive cells and doublecortin/5-bromodeoxyuridine (BrdU)-double-positive cells was decreased in the SGZ of Nb-infected mice by day 9 after infection. However, the total number of BrdU-positive newborn cells in the SGZ did not change. In no significant alterations were detected in the SVZ of infected mice. In addition, using reverse transcription-quantitative polymerase chain reaction, we observed no significant changes in the expression levels of neurotropic factors important for neurogenesis in the hippocampus. In conclusion, our results indicate that adult neurogenesis in SGZ, but not in SVZ, is inhibited by Nb infection. Th2 immune response might have a suppressive effect on hippocampal neurogenesis.

IL-4 up-regulates cyclooxygenase-1 expression in macrophages.

Macrophages use various cell-surface receptors to sense their environment and undergo polarized responses. The cytokines, interleukin (IL)-4 and IL-13, released from T-helper type 2 (Th2) cells, drive macrophage polarization toward an alternatively activated phenotype (M2). This phenotype is associated with the expression of potent pro-resolving mediators, such as the prostaglandin (PG) D2-derived cyclopentenone metabolite, 15d-PGJ2, produced by the cyclooxygenase (Ptgs; Cox) pathway. Interestingly, IL-4 treatment of bone marrow-derived macrophages (BMDMs) significantly down-regulates Cox-2 protein expression, whereas Cox-1 levels are significantly increased. This phenomenon not only challenges the dogma that Cox-1 is only developmentally regulated, but also demonstrates a novel mechanism in which IL-4-dependent regulation of Cox-1 involves the activation of the mechanistic target of rapamycin complex (mTORC). Using specific chemical inhibitors, we demonstrate here that IL-4-dependent Cox-1 up-regulation occurs at the post-transcriptional level via the Fes-Akt-mTORC axis. Activation of AMP-activated protein kinase (AMPK) by metformin, inhibition of mTORC by torin 1, or CRISPR/Cas9-mediated genetic knock-out of tuberous sclerosis complex-2 (Tsc2) blocked the IL-4-dependent expression of Cox-1 and the ability of macrophages to polarize to M2. However, use of 15d-PGJ2 partially rescued the effects of AMPK activation, suggesting the importance of Cox-1 in macrophage polarization as also observed in a model of gastrointestinal helminth clearance. In summary, these findings suggest a new paradigm where IL-4-dependent up-regulation of Cox-1 expression may play a key role in tissue homeostasis and wound healing during Th2-mediated immune responses, such as parasitic infections.

Host- and Helminth-Derived Endocannabinoids That Have Effects on Host Immunity Are Generated during Infection.

Helminths have coevolved with their hosts, resulting in the development of specialized host immune mechanisms and parasite-specific regulatory products. Identification of new pathways that regulate helminth infection could provide a better understanding of host-helminth interaction and may identify new therapeutic targets for helminth infection. Here we identify the endocannabinoid system as a new mechanism that influences host immunity to helminths. Endocannabinoids are lipid-derived signaling molecules that control important physiologic processes, such as feeding behavior and metabolism. Following murine infection with Nippostrongylus brasiliensis, an intestinal nematode with a life cycle similar to that of hookworms, we observed increased levels of endocannabinoids (2-arachidonoylglycerol [2-AG] or anandamide [AEA]) and the endocannabinoid-like molecule oleoylethanolamine (OEA) in infected lung and intestine. To investigate endocannabinoid function in helminth infection, we employed pharmacological inhibitors of cannabinoid subtype receptors 1 and 2 (CB1R and CB2R). Compared to findings for vehicle-treated mice, inhibition of CB1R but not CB2R resulted in increased N. brasiliensis worm burden and egg output, associated with significantly decreased expression of the T helper type 2 cytokine interleukin 5 (IL-5) in intestinal tissue and splenocyte cultures. Strikingly, bioinformatic analysis of genomic and transcriptome sequencing (RNA-seq) data sets identified putative genes encoding endocannabinoid biosynthetic and degradative enzymes in many parasitic nematodes. To test the novel hypothesis that helminth parasites produce their own endocannabinoids, we measured endocannabinoid levels in N. brasiliensis by mass spectrometry and quantitative PCR and found that N. brasiliensis parasites produced endocannabinoids, especially at the infectious larval stage. To our knowledge, this is the first report of helminth- and host-derived endocannabinoids that promote host immune responses and reduce parasite burden.