Innate immune responses to lung-stage helminth infection induce alternatively activated alveolar macrophages

Hookworms dynamically respond to loss of Type 2 immune pressure

The impact of the host immune environment on parasite transcription and fitness is currently unknown. It is widely held that hookworm infections have an immunomodulatory impact on the host, but whether the converse is true remains unclear. Immunity against adult-stage hookworms is largely mediated by Type 2 immune responses driven by the transcription factor Signal Transducer and Activator of Transcription 6 (STAT6). This study investigated whether serial passage of the rodent hookworm Nippostrongylus brasiliensis in STAT6-deficient mice (STAT6 KO) caused changes in parasites over time. After adaptation to STAT6 KO hosts, N. brasiliensis increased their reproductive output, feeding capacity, energy content, and body size. Using an improved N. brasiliensis genome, we found that these physiological changes corresponded with a dramatic shift in the transcriptional landscape, including increased expression of gene pathways associated with egg production, but a decrease in genes encoding neuropeptides, proteases, SCP/TAPS proteins, and transthyretin-like proteins; the latter three categories have been repeatedly observed in hookworm excreted/secreted proteins (ESPs) implicated in immunosuppression. Although transcriptional changes started to appear in the first generation of passage in STAT6 KO hosts for both immature and mature adult stages, downregulation of the genes putatively involved in immunosuppression was only observed after multiple generations in this immunodeficient environment. When STAT6 KO-adapted N. brasiliensis were reintroduced to a naive WT host after up to 26 generations, this progressive change in host-adaptation corresponded to increased production of inflammatory cytokines by the WT host. Surprisingly, however, this single exposure of STAT6 KO-adapted N. brasiliensis to WT hosts resulted in worms that were morphologically and transcriptionally indistinguishable from WT-adapted parasites. This work uncovers remarkable plasticity in the ability of hookworms to adapt to their hosts, which may present a general feature of parasitic nematodes.

Myeloid- and epithelial-derived RELMα contribute to tissue repair following lung helminth infection

Soil-transmitted helminth (STH) infections impact billions of individuals globally; however, there is a need to clarify the long-term impacts of these infections on pulmonary health owing to their transient migration and subsequent damage to the lungs. In mouse models of these infections using Nippostrongylus brasiliensis, lung pathology persists at later time points post single infection. These studies also indicate the persistent transcriptional expression of resistin-like molecule α (RELMα), an immunomodulatory protein induced in type 2 immunity and alternatively activated macrophages. Using constitutive and tamoxifen-inducible cell-specific RELMα knockout mouse strains, we identified that epithelial- and myeloid-derived RELMα protein remained elevated at 30 days post infection and altered the immune cell signature and gene expression in lung compartments. Histopathological assessment of alveolar damage revealed a role for RELMα in tissue repair, suggesting the importance of sustained RELMα expression for lung recovery from helminth infection. Acellular three-dimensional (3D) lung scaffolds were prepared from the lungs of wild-type (WT), RELMα KO-naive, or 30 days post N. brasiliensis-infected mice to assess their ability to support epithelial cell growth. N. brasiliensis infection significantly altered the scaffold and impaired epithelial cell growth and metabolic activity, especially in the RELMα KO scaffolds. These findings underscore a need to identify the long-term impacts of helminth infection on human pulmonary disease, particularly as alveolar destruction can develop into chronic obstructive pulmonary disease (COPD), which remains among the top global causes of death. Translation of these findings to human protein resistin, with sequence homology to RELMα therapeutic opportunities in lung repair.

A succinate/SUCNR1-brush cell defense program in the tracheal epithelium

Host-derived succinate accumulates in the airways during bacterial infection. Here, we show that luminal succinate activates murine tracheal brush (tuft) cells through a signaling cascade involving the succinate receptor 1 (SUCNR1), phospholipase Cβ2, and the cation channel transient receptor potential channel subfamily M member 5 (TRPM5). Stimulated brush cells then trigger a long-range Ca2+ wave spreading radially over the tracheal epithelium through a sequential signaling process. First, brush cells release acetylcholine, which excites nearby cells via muscarinic acetylcholine receptors. From there, the Ca2+ wave propagates through gap junction signaling, reaching also distant ciliated and secretory cells. These effector cells translate activation into enhanced ciliary activity and Cl- secretion, which are synergistic in boosting mucociliary clearance, the major innate defense mechanism of the airways. Our data establish tracheal brush cells as a central hub in triggering a global epithelial defense program in response to a danger-associated metabolite.

Single-Walled vs. Multi-Walled Carbon Nanotubes: Influence of Physico-Chemical Properties on Toxicogenomics Responses in Mouse Lungs

Single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) are nanomaterials with one or multiple layers of carbon sheets. While it is suggested that various properties influence their toxicity, the specific mechanisms are not completely known. This study was aimed to determine if single or multi-walled structures and surface functionalization influence pulmonary toxicity and to identify the underlying mechanisms of toxicity. Female C57BL/6J BomTac mice were exposed to a single dose of 6, 18, or 54 μg/mouse of twelve SWCNTs or MWCNTs of different properties. Neutrophil influx and DNA damage were assessed on days 1 and 28 post-exposure. Genome microarrays and various bioinformatics and statistical methods were used to identify the biological processes, pathways and functions altered post-exposure to CNTs. All CNTs were ranked for their potency to induce transcriptional perturbation using benchmark dose modelling. All CNTs induced tissue inflammation. MWCNTs were more genotoxic than SWCNTs. Transcriptomics analysis showed similar responses across CNTs at the pathway level at the high dose, which included the perturbation of inflammatory, cellular stress, metabolism, and DNA damage responses. Of all CNTs, one pristine SWCNT was found to be the most potent and potentially fibrogenic, so it should be prioritized for further toxicity testing.

Trickle infection with Heligmosomoides polygyrus results in decreased worm burdens but increased intestinal inflammation and scarring

Introduction

Intestinal roundworms cause chronic debilitating disease in animals, including humans. Traditional experimental models of these types of infection use a large single-dose infection. However, in natural settings, hosts are exposed to parasites on a regular basis and when mice are exposed to frequent, smaller doses of Heligmosomoides polygyrus, the parasites are cleared more quickly. Whether this more effective host response has any negative consequences for the host is not known.

Results

Using a trickle model of infection, we found that worm clearance was associated with known resistance-related host responses: increased granuloma and tuft cell numbers, increased levels of granuloma IgG and decreased intestinal transit time, as well as higher serum IgE levels. However, we found that the improved worm clearance was also associated with an inflammatory phenotype in and around the granuloma, increased smooth muscle hypertrophy/hyperplasia, and elevated levels of Adamts gene expression.

Discussion

To our knowledge, we are the first to identify the involvement of this protein family of matrix metalloproteinases (MMPs) in host responses to helminth infections. Our results highlight the delicate balance between parasite clearance and host tissue damage, which both contribute to host pathology. When continually exposed to parasitic worms, improved clearance comes at a cost.

Nitric oxide in parasitic infections: a friend or foe?

The complex interaction between the host and the parasite remains a puzzling question. Control of parasitic infections requires an efficient immune response that must be balanced against destructive pathological consequences. Nitric oxide is a nitrogenous free radical which has many molecular targets and serves diverse functions. Apart from being a signaling messenger, nitric oxide is critical for controlling numerous infections. There is still controversy surrounding the exact role of nitric oxide in the immune response against different parasitic species. It proved protective against intracellular protozoa, as well as extracellular helminths. At the same time, it plays a pivotal role in stimulating detrimental pathological changes in the infected hosts. Several reports have discussed the anti-parasitic and immunoregulatory functions of nitric oxide, which could directly influence the control of the infection. Nevertheless, there is scarce literature addressing the harmful cytotoxic impacts of this mediator. Thus, this review provides insights into the most updated concepts and controversies regarding the dual nature and opposing sides of nitric oxide during the course of different parasitic infections.

Communication is key: Innate immune cells regulate host protection to helminths

Parasitic helminth infections remain a significant global health issue and are responsible for devastating morbidity and economic hardships. During infection, helminths migrate through different host organs, which results in substantial tissue damage and the release of diverse effector molecules by both hematopoietic and non-hematopoietic cells. Thus, host protective responses to helminths must initiate mechanisms that help to promote worm clearance while simultaneously mitigating tissue injury. The specialized immunity that promotes these responses is termed type 2 inflammation and is initiated by the recruitment and activation of hematopoietic stem/progenitor cells, mast cells, basophils, eosinophils, dendritic cells, neutrophils, macrophages, myeloid-derived suppressor cells, and group 2 innate lymphoid cells. Recent work has also revealed the importance of neuron-derived signals in regulating type 2 inflammation and antihelminth immunity. These studies suggest that multiple body systems coordinate to promote optimal outcomes post-infection. In this review, we will describe the innate immune events that direct the scope and intensity of antihelminth immunity. Further, we will highlight the recent progress made in our understanding of the neuro-immune interactions that regulate these pathways and discuss the conceptual advances they promote.

Monocytes maintain central nervous system homeostasis following helminth-induced inflammation

Neuroimmune interactions are crucial for regulating immunity and inflammation. Recent studies have revealed that the central nervous system (CNS) senses peripheral inflammation and responds by releasing molecules that limit immune cell activation, thereby promoting tolerance and tissue integrity. However, the extent to which this is a bidirectional process, and whether peripheral immune cells also promote tolerance mechanisms in the CNS remains poorly defined. Here we report that helminth-induced type 2 inflammation promotes monocyte responses in the brain that are required to inhibit excessive microglial activation and host death. Mechanistically, infection-induced monocytes express YM1 that is sufficient to inhibit tumor necrosis factor production from activated microglia. Importantly, neuroprotective monocytes persist in the brain, and infected mice are protected from subsequent lipopolysaccharide-induced neuroinflammation months after infection-induced inflammation has resolved. These studies demonstrate that infiltrating monocytes promote CNS homeostasis in response to inflammation in the periphery and demonstrate that a peripheral infection can alter the immunologic landscape of the host brain.

Tissue-specific immunity in helminth infections

A characteristic feature of host responses to helminth infections is the development of profound systemic and tissue-localised Type 2 immune responses that play critical roles in immunity, tissue repair and tolerance of the parasite at tissue sites. These same Type 2 responses are also seen in the tissue-associated immune-pathologies seen in asthma, atopic dermatitis and many forms of allergies. The recent identification of new subtypes of immune cells and cytokine pathways that influence both immune and non-immune cells and tissues creates the opportunity for reviewing helminth parasite-host responses in the context of tissue specific immunity. This review focuses on the new discoveries of the cells and cytokines involved in tissue specific immune responses to helminths and how these contribute to host immunity against helminth infection and allow the host to accommodate the presence of parasites when they cannot be eliminated.

Transient Ascaris suum larval migration induces intractable chronic pulmonary disease and anemia in mice

Ascariasis is one of the most common infections in the world and associated with significant global morbidity. Ascaris larval migration through the host’s lungs is essential for larval development but leads to an exaggerated type-2 host immune response manifesting clinically as acute allergic airway disease. However, whether Ascaris larval migration can subsequently lead to chronic lung diseases remains unknown. Here, we demonstrate that a single episode of Ascaris larval migration through the host lungs induces a chronic pulmonary syndrome of type-2 inflammatory pathology and emphysema accompanied by pulmonary hemorrhage and chronic anemia in a mouse model. Our results reveal that a single episode of Ascaris larval migration through the host lungs leads to permanent lung damage with systemic effects. Remote episodes of ascariasis may drive non-communicable lung diseases such as asthma, chronic obstructive pulmonary disease (COPD), and chronic anemia in parasite endemic regions.

Ascariasis is the most common helminth infection and leads to significant global morbidity. Transient Ascaris larval migration through the host’s lungs is essential for larval development but leads to an exaggerated type-2 host immune response. Our work demonstrates that transient Ascaris spp. larval migration through the lungs has significant long-term consequences including changes in lung structure and function as well as vascular damage causing chronic lung disease and anemia. We propose that Ascaris spp. larval migration through the host lungs is a risk factor for the development of chronic lung disease and anemia in parasite-endemic regions globally.

IL-13 deficiency exacerbates lung damage and impairs epithelial-derived type 2 molecules during nematode infection

IL-13 is implicated in effective repair after acute lung injury and the pathogenesis of chronic diseases such as allergic asthma. Both these processes involve matrix remodelling, but understanding the specific contribution of IL-13 has been challenging because IL-13 shares receptors and signalling pathways with IL-4. Here, we used Nippostrongylus brasiliensis infection as a model of acute lung damage comparing responses between WT and IL-13-deficient mice, in which IL-4 signalling is intact. We found that IL-13 played a critical role in limiting tissue injury and haemorrhaging in the lung, and through proteomic and transcriptomic profiling, identified IL-13-dependent changes in matrix and associated regulators. We further showed a requirement for IL-13 in the induction of epithelial-derived type 2 effector molecules such as RELM-α and surfactant protein D. Pathway analyses predicted that IL-13 induced cellular stress responses and regulated lung epithelial cell differentiation by suppression of Foxa2 pathways. Thus, in the context of acute lung damage, IL-13 has tissue-protective functions and regulates epithelial cell responses during type 2 immunity.

Cannabinoid Receptor Subtype-1 Regulates Allergic Airway Eosinophilia During Lung Helminth Infection

Introduction: Over 1 billion humans carry infectious helminth parasites that can lead to chronic comorbidities such as anemia and growth retardation in children. Helminths induce a T-helper type 2 (Th2) immune response in the host and can cause severe tissue damage and fibrosis if chronic. We recently reported that mice infected with the soil-transmitted helminth, Nippostrongylus brasiliensis, displayed elevated levels of endocannabinoids (eCBs) in the lung and intestine. eCBs are lipid-signaling molecules that control inflammation; however, their function in infection is not well defined. Materials and Methods: A combination of pharmacological approaches and genetic mouse models was used to investigate roles for the eCB system in inflammatory responses and lung injury in mice during parasitic infection with N. brasiliensis. Results: Hemorrhaging of lung tissue in mice infected with N. brasiliensis was exacerbated by inhibiting peripheral cannabinoid receptor subtype-1 (CB1Rs) with the peripherally restricted CB1R antagonist, AM6545. In addition, these mice exhibited an increase in nonfunctional alveolar space and prolonged airway eosinophilia compared to vehicle-treated infected mice. In contrast to mice treated with AM6545, infected cannabinoid receptor subtype-2-null mice (Cnr2-/-) did not display any changes in these parameters compared to wild-type mice. Conclusions: Roles for the eCB system in Th2 immune responses are not well understood; however, increases in its activity in response to infection suggest an immunomodulatory role. Moreover, these findings suggest a role for eCB signaling at CB1Rs but not cannabinoid receptor subtypes-2 in the resolution of Th2 inflammatory responses, which become host destructive over time.

Comparative Transcriptomics of IBD Patients Indicates Induction of Type 2 Immunity Irrespective of the Disease Ideotype

Inflammatory cytokines initiate and sustain the perpetuation of processes leading to chronic inflammatory conditions such as inflammatory bowel diseases (IBD). The nature of the trigger causing an inflammatory reaction decides whether type 1, type 17, or type 2 immune responses, typically characterized by the respective T- helper cell subsets, come into effect. In the intestine, Type 2 responses have been linked with mucosal healing and resolution upon an immune challenge involving parasitic infections. However, type 2 cytokines are frequently elevated in certain types of IBD in particular ulcerative colitis (UC) leading to the assumption that Th2 cells might critically support the pathogenesis of UC raising the question of whether such elevated type 2 responses in IBD are beneficial or detrimental. In line with this, previous studies showed that suppression of IL-13 and other type 2 related molecules in murine models could improve the outcomes of intestinal inflammation. However, therapeutic attempts of neutralizing IL-13 in ulcerative colitis patients have yielded no benefits. Thus, a better understanding of the role of type 2 cytokines in regulating intestinal inflammation is required. Here, we took a comparative transcriptomic approach to address how Th2 responses evolve in different mouse models of colitis and human IBD datasets. Our data show that type 2 immune-related transcripts are induced in the inflamed gut of IBD patients in both Crohn's disease and UC and across widely used mouse models of IBD. Collectively our data implicate that the presence of a type 2 signature rather defines a distinct state of intestinal inflammation than a disease-specific pathomechanism.

Helminth Antigen Exposure Enhances Early Immune Control of Mycobacterium tuberculosis in Monocytes and Macrophages

Helminth and Mycobacterium tuberculosis (Mtb) coinfection is common and suggested to influence the risk of developing active tuberculosis (TB). It is known that helminths in contrast to TB induce a strong Th2 response in the host. However, the direct impact of helminth antigen exposure on host immunity against TB is largely unknown. Our aim was to explore the effects of helminth antigen exposure on the early immune control of Mtb in monocytes and macrophages. Ascaris lumbricoides (ASC) and Schistosoma mansoni (SM) protein antigens were used to study the immediate effect of helminth antigen exposure in monocytes, on monocyte-to-macrophage differentiation, or mature macrophages, in the control of virulent Mtb H37Rv. Pre-exposure of peripheral blood mononuclear cells reduced Mtb growth in monocytes, especially with SM, but no Th1/Th2 cytokines or activation markers indicated involvement of T cells. Monocytes exposed before maturing into macrophages reduced Mtb growth in macrophages (ASC), and pre-exposure of mature macrophages reduced (ASC) or kept Mtb growth at control levels (SM). This in vitro model shows how helminth infection directly affects the monocyte-macrophage axis at an early stage before cell-mediated immunity develops. During acute helminth coinfection or when helminth antigen concentration is elevated at the site of Mtb infection, these helminths provide an enhanced control and killing of Mtb owing to the direct stimulatory effect of helminth antigens on phagocytic cells.

Host Immunity and Inflammation to Pulmonary Helminth Infections

Helminths, including nematodes, cestodes and trematodes, are complex parasitic organisms that infect at least one billion people globally living in extreme poverty. Helminthic infections are associated with severe morbidity particularly in young children who often harbor the highest burden of disease. While each helminth species completes a distinct life cycle within the host, several helminths incite significant lung disease. This impact on the lungs occurs either directly from larval migration and host immune activation or indirectly from a systemic inflammatory immune response. The impact of helminths on the pulmonary immune response involves a sophisticated orchestration and activation of the host innate and adaptive immune cells. The consequences of activating pulmonary host immune responses are variable with several helminthic infections leading to severe, pulmonary compromise while others providing immune tolerance and protection against the development of pulmonary diseases. Further delineation of the convoluted interface between helminth infection and the pulmonary host immune responses is critical to the development of novel therapeutics that are critically needed to prevent the significant global morbidity caused by these parasites.

RELMα-expressing macrophages protect against fatal lung damage and reduce parasite burden during helminth infection

Alternatively activated macrophages (AAMs) can contribute to wound healing, regulation of glucose and fat metabolism, resolution of inflammation, and protective immunity against helminths. Their differentiation, tissue distribution, and effector functions are incompletely understood. Murine AAMs express high levels of resistin-like molecule (RELM) α, an effector protein with potent immunomodulatory functions. To visualize RELMα⁺ macrophages (MΦs) in vivo and evaluate their role in defense against helminths, we generated RELMα reporter/deleter mice. Infection with the helminth Nippostrongylus brasiliensis induced expansion of RELMα⁺ lung interstitial but not alveolar MΦs in a STAT6-dependent manner. RELMα⁺ MΦs were required for prevention of fatal lung damage during primary infection. Furthermore, protective immunity was lost upon specific deletion of RELMα⁺ MΦs during secondary infection. Thus, RELMα reporter/deleter mice reveal compartmentalization of AAMs in different tissues and demonstrate their critical role in resolution of severe lung inflammation and protection against migrating helminths.

Deletion of Chitinase-3-like 1 accelerates stroke development through enhancement of Neuroinflammation by STAT6-dependent M2 microglial inactivation in Chitinase-3-like 1 knockout mice

Chitinase 3-like 1 (Chi3L1) plays a major role in the pathogenesis of inflammatory diseases. We investigated the effect of Chi3L1 knockout on stroke development. Ischemia/reperfusion was induced by middle cerebral artery occlusion (MCAO) in Chi3L1 knockout and wildtype mice. Significantly increased infarct volume and decreased neurological deficit scores at 24 h after ischemia/reperfusion were found in Chi3L1 knockout mice compared to wildtype mice. Moreover, ischemic neuronal cell death was increased in Chi3L1 knockout mice through increased oxidative stress and release of IL-6 and IL-1β but IL-10 and IL-4 were reduced. Furthermore, expression of inflammation-related proteins (iNOS, COX-2, Iba-1, and GFAP) was significantly increased in Chi3L1 knockout mice compared to wildtype. In microglia isolated from MCAO-injured Chi3L1 knockout mice, expression of M1 markers (iNOS, CD86, IL-1β, and IL-6) was increased and M2 markers (Arg1, Mrc1, IL-10, and IL-4Ra) was decreased. In BV-2 cells, knockdown of Chi3L1 increased TNF-α- and INF-γ-induced expression of iNOS, COX-2, and Iba-1, but decreased the expression of Arg1, MRC1, and IL-4 receptor-alpha (IL-4Rα). Expression of IL-4Rα, an important factor of M2 polarization, and its downstream signals p-JAK1, p-JAK3, and p-STAT6, was much reduced in the knockout mice. Additionally, in BV-2 cells, knockdown of Chi3L1 by siRNA Chi3L1 decreased rhTNF-α- and INF-γ-induced expression of IL-4Rα, p-JAK1, p-JAK3, and p-STAT6. Furthermore, treatment with AS1517499 abolished Chi3L1 knockdown-induced reduced IL-4Rα and Arg1 but not CD86 expression. Our results indicate that deletion of Chi3L1 accelerates stroke development through enhancement of neuroinflammation by markedly decreasing STAT6-dependent M2 macrophage polarization.

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.

Azithromycin Polarizes Macrophages to an M2 Phenotype via Inhibition of the STAT1 and NF-κB Signaling Pathways

Azithromycin is effective at controlling exaggerated inflammation and slowing the long-term decline of lung function in patients with cystic fibrosis. We previously demonstrated that the drug shifts macrophage polarization toward an alternative, anti-inflammatory phenotype. In this study we investigated the immunomodulatory mechanism of azithromycin through its alteration of signaling via the NF-κB and STAT1 pathways. J774 murine macrophages were plated, polarized (with IFN-γ, IL-4/-13, or with azithromycin plus IFN-γ) and stimulated with LPS. The effect of azithromycin on NF-κB and STAT1 signaling mediators was assessed by Western blot, homogeneous time-resolved fluorescence assay, nuclear translocation assay, and immunofluorescence. The drug's effect on gene and protein expression of arginase was evaluated as a marker of alternative macrophage activation. Azithromycin blocked NF-κB activation by decreasing p65 nuclear translocation, although blunting the degradation of IκBα was due, at least in part, to a decrease in IKKβ kinase activity. A direct correlation was observed between increasing azithromycin concentrations and increased IKKβ protein expression. Moreover, incubation with the IKKβ inhibitor IKK16 decreased arginase expression and activity in azithromycin-treated cells but not in cells treated with IL-4 and IL-13. Importantly, azithromycin treatment also decreased STAT1 phosphorylation in a concentration-dependent manner, an effect that was reversed with IKK16 treatment. We conclude that azithromycin anti-inflammatory mechanisms involve inhibition of the STAT1 and NF-κB signaling pathways through the drug's effect on p65 nuclear translocation and IKKβ.

The lung environment controls alveolar macrophage metabolism and responsiveness in type 2 inflammation

Fine control of macrophage activation is needed to prevent inflammatory disease, particularly at barrier sites such as the lungs. However, the dominant mechanisms that regulate the activation of pulmonary macrophages during inflammation are poorly understood. We found that alveolar macrophages (AlvMs) were much less able to respond to the canonical type 2 cytokine IL-4, which underpins allergic disease and parasitic worm infections, than macrophages from lung tissue or the peritoneal cavity. We found that the hyporesponsiveness of AlvMs to IL-4 depended upon the lung environment but was independent of the host microbiota or the lung extracellular matrix components surfactant protein D (SP-D) and mucin 5b (Muc5b). AlvMs showed severely dysregulated metabolism relative to that of cavity macrophages. After removal from the lungs, AlvMs regained responsiveness to IL-4 in a glycolysis-dependent manner. Thus, impaired glycolysis in the pulmonary niche regulates AlvM responsiveness during type 2 inflammation.

Human Hookworm Infection Enhances Mycobacterial Growth Inhibition and Associates With Reduced Risk of Tuberculosis Infection

Soil-transmitted helminths and Mycobacterium tuberculosis frequently coincide geographically and it is hypothesized that gastrointestinal helminth infection may exacerbate tuberculosis (TB) disease by suppression of Th1 and Th17 responses. However, few studies have focused on latent TB infection (LTBI), which predominates globally. We performed a large observational study of healthy adults migrating from Nepal to the UK (n = 645). Individuals were screened for LTBI and gastrointestinal parasite infections. A significant negative association between hookworm and LTBI-positivity was seen (OR = 0.221; p = 0.039). Hookworm infection treatment did not affect LTBI conversions. Blood from individuals with hookworm had a significantly greater ability to control virulent mycobacterial growth in vitro than from those without, which was lost following hookworm treatment. There was a significant negative relationship between mycobacterial growth and eosinophil counts. Eosinophil-associated differential gene expression characterized the whole blood transcriptome of hookworm infection and correlated with improved mycobacterial control. These data provide a potential alternative explanation for the reduced prevalence of LTBI among individuals with hookworm infection, and possibly an anti-mycobacterial role for helminth-induced eosinophils.

Professional and 'Amateur' Antigen-Presenting Cells In Type 2 Immunity

Dendritic cells (DCs) are critical for the activation of naïve CD4⁺ T cells and are considered professional antigen-presenting cells (APCs), as are macrophages and B cells. Recently, several innate type 2 immune cells, such as basophils, mast cells (MCs), eosinophils, and innate type 2 lymphocytes (ILC2), have also emerged as harboring APC behavior. Through surface expression or transfer of peptide-loaded MHCII, expression of costimulatory and co-inhibitory molecules, as well as the secretion of polarizing cytokines, these innate cells can extensively communicate with effector and regulatory CD4⁺ T cells. An exciting new concept is that the complementary tasks of these 'amateur' APCs contribute to shaping and regulating adaptive immunity to allergens and helminths, often in collaboration with professional APCs.

First Responders: Innate Immunity to Helminths

Helminth infections represent a significant public health concern resulting in devastating morbidity and economic consequences across the globe. Helminths migrate through mucosal sites causing tissue damage and the induction of type 2 immune responses. Antihelminth protection relies on the mobilization and activation of multiple immune cells, including type 2 innate lymphocytes (ILC2s), basophils, mast cells, macrophages, and hematopoietic stem/progenitor cells. Further, epithelial cells and neurons have been recognized as important regulators of type 2 immunity. Collectively, these pathways stimulate host-protective responses necessary for worm expulsion and the healing of affected tissues. In this review we focus on the innate immune pathways that regulate immunity to helminth parasites and describe how better understanding of these pathways may lead to the development of new therapeutic strategies.

Nippostrongylus brasiliensis infection leads to impaired reference memory and myeloid cell interference

Hookworm infection is endemic in developing countries, leading to poor cognitive function-among other disruptions. In this study, the effects of Nippostrongylus brasiliensis infection (a murine model of Necator Americanus) on cognitive function were investigated. Though impaired cognition has been extensively reported, the exact domain of cognition affected is still unknown, hence requiring investigation. The objective of this study was to identify possible cognitive changes during Nippostrongylus brasiliensis infection in mice, using the Morris water maze. Here, we show for the first time that mice infected with Nippostrongylus brasiliensis were able to learn the Morris water maze task, but demonstrated impaired reference memory. Anxiety measured by thigmotaxis in the maze, did not play a role for the observed cognitive impairment. Of further interest, an increase in the number of hippocampal macrophages and microglia with training and/or infection suggested a significant role of these cell types during spatial learning. Together, these experimental mouse studies suggest that helminth infections do have an impact on cognition. Further experimental animal studies on cognition and infection might open new approaches for a better understanding and impact of pathogen infections.

A Role for the Krebs Cycle Intermediate Citrate in Metabolic Reprogramming in Innate Immunity and Inflammation

Metabolism in immune cells is no longer thought of as merely a process for adenosine triphosphate (ATP) production, biosynthesis, and catabolism. The reprogramming of metabolic pathways upon activation is also for the production of metabolites that can act as immune signaling molecules. Activated dendritic cells (DCs) and macrophages have an altered Krebs cycle, one consequence of which is the accumulation of both citrate and succinate. Citrate is exported from the mitochondria via the mitochondrial citrate- carrier. Cytosolic metabolism of citrate to acetyl-coenzyme A (acetyl-CoA) is important for both fatty-acid synthesis and protein acetylation, both of which have been linked to macrophage and DC activation. Citrate-derived itaconate has a direct antibacterial effect and also has been shown to act as an anti-inflammatory agent, inhibiting succinate dehydrogenase. These findings identify citrate as an important metabolite for macrophage and DC effector function.

Chi3l3: a potential key orchestrator of eosinophil recruitment in meningitis induced by Angiostrongylus cantonensis

BACKGROUND

Angiostrongylus cantonensis, an important foodborne parasite, can induce serious eosinophilic meningitis in non-permissive hosts, such as mouse and human. However, the characteristics and mechanisms of the infection are still poorly understood. This study sought to determine the key molecules and its underlying mechanism in inducing brain eosinophilic infiltration caused by Angiostrongylus cantonensis.

METHODS

Mathematical models were established for prediction of significantly changing genes and the functional associated protein with RNA-seq data in Angiostrongylus cantonensis infection. The expression level of Chi3l3, the predicted key molecule, was verified using Western blotting and real-time quantitative PCR. Critical cell source of Chi3l3 and its relationship with eosinophils were identified with flow cytometry, immunohistochemistry, and further verified by macrophage depletion using liposomal clodronate. The role of soluble antigens of Angiostrongylus cantonensis in eosinophilic response was identified with mice airway allergy model by intranasal administration of Alternaria alternate. The relationship between Chi3l3 and IL-13 was identified with flow cytometry, Western blotting, and Seahorse Bioscience extracellular flux analyzer.

RESULTS

We analyzed the skewed cytokine pattern in brains of Angiostrongylus cantonensis-infected mice and found Chi3l3 to be an important molecule, which increased sharply during the infection. The percentage of inflammatory macrophages, the main source of Chi3l3, also increased, in line with eosinophils percentage in the brain. Network analysis and mathematical modeling predirect a functional association between Chi3l3 and IL-13. Further experiments verified that the soluble antigen of Angiostrongylus cantonensis induce brain eosinophilic meningitis via aggravating a positive feedback loop between IL-13 and Chi3l3.

CONCLUSIONS

We present evidences in favor of a key role for macrophave-derived Chi3l3 molecule in the infection of Angiostrongylus cantonensis, which aggravates eosinophilic meningitis induced by Angiostrongylus cantonensis via a IL-13-mediated positive feedback loop. These reported results constitute a starting point for future research of angiostrongyliasis pathogenesis and imply that targeting chitinases and chitinase-like-proteins may be clinically beneficial in Angiostrongylus cantonensis-induced eosinophilic meningitis.

Chitinase-like proteins as regulators of innate immunity and tissue repair: helpful lessons for asthma?

Chitinases and chitinase-like proteins (CLPs) belong to the glycoside hydrolase family 18 of proteins. Chitinases are expressed in mammals and lower organisms, facilitate chitin degradation, and hence act as host-defence enzymes. Gene duplication and loss-of-function mutations of enzymatically active chitinases have resulted in the expression of a diverse range of CLPs across different species. CLPs are genes that are increasingly associated with inflammation and tissue remodelling not only in mammals but also across distant species. While the focus has remained on understanding the functions and expression patterns of CLPs during disease in humans, studies in mouse and lower organisms have revealed important and overlapping roles of the CLP family during physiology, host defence and pathology. This review will summarise recent insights into the regulatory functions of CLPs on innate immune pathways and discuss how these effects are not only important for host defence and tissue injury/repair after pathogen invasion, but also how they have extensive implications for pathological processes involved in diseases such as asthma.

Interleukin-13/interleukin-4 receptor pathway is crucial for production of Sda-sialomucin in mouse small intestinal mucosa by Nippostrongylus brasiliensis infection

Mucin is a major component of mucus in gastrointestinal mucosa. Increase of specific sialomucins having Sd^a blood group antigen, NeuAcα2-3(GalNAcβ1-4)Galβ1-4GlcNAcβ-, is considered to be associated with expulsion of the parasitic intestinal nematode Nippostrongylus brasiliensis. In this study, we examined the relationship between interleukin (IL)-13 pathway and expression of Sd^a-sialomucins in small intestinal mucosa with N. brasiliensis infection. Nematode infection induced marked increases in small intestinal mucins that reacted with anti-Sd^a antibody in wild type (wt) mice. However, this increase due to infection was supressed in IL-4 receptor α deficient (IL-4Rα^-/-) mice, which lack both IL-4 and IL-13 signaling via IL-4R, and severe combined immunodeficient (SCID) mice, which have defects in B- and T-lymphocytes. Analysis using tandem mass spectroscopy showed that Sd^a-glycans were not expressed in small intestinal mucins in IL-4Rα^-/- and SCID mice after infection despite the appearance of Sd^a-glycans in the infected wt mice. Inoculation of recombinant IL-13 into the infected SCID mice restored expression of Sd^a-glycan. Our results suggest that the IL-13/IL-4R axis is important for the production of Sd^a-sialomucins in the host intestinal mucosa with parasitic nematode infection.

Myeloid Cell Phenotypes in Susceptibility and Resistance to Helminth Parasite Infections

Many major tropical diseases are caused by long-lived helminth parasites that are able to survive by modulation of the host immune system, including the innate compartment of myeloid cells. In particular, dendritic cells and macrophages show markedly altered phenotypes during parasite infections. In addition, many specialized subsets such as eosinophils and basophils expand dramatically in response to these pathogens. The changes in phenotype and function, and their effects on both immunity to infection and reactivity to bystander antigens such as allergens, are discussed.

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.

Mycobacteria induce TPL-2 mediated IL-10 in IL-4-generated alternatively activated macrophages

IL-4 drives expansion of Th2 cells that cause generation of alternatively activated macrophages (AAMs). Filarial infections are established early in life, induce increased IL-4 production are co-endemic with tuberculosis (TB). We sought to understand, therefore, how mycobacteria are handled in the context of IL-4-induced AAM. Comparing IL-4 generated in vitro monocyte derived human AAMs to LPS and IFN-γ generated classically macrophages (CAMs), both infected with mycobacteria (BCG), we demonstrated increased early BCG uptake and increased IL-10 production in AAMs compared to CAMs. We further demonstrated that increased IL-10 production is mediated by upregulation of tumor progression locus 2 (TPL-2), an upstream activator of extracellular signal related kinases (ERKs) in AAMs but not in CAMs, both at the transcript as well as the protein level. Pharmacologic inhibition of TPL-2 significantly diminished IL-10 production only in BCG-infected AAMs. Finally, we validated our findings in an in vivo C57Bl/6 model of filarial infection, where an exaggerated Th2 induced lung-specific alternative activation led to TPL-2 and IL-10 upregulation on subsequent TB infection. These data show that in response to mycobacterial infection, IL-4 generated AAMs in chronic filarial infections have impaired immune responses to TB infection by increasing IL-10 production in a TPL-2 mediated manner.

New perspectives on the regulation of type II inflammation in asthma

Asthma is a chronic inflammatory disease of the lungs which has been thought to arise as a result of inappropriately directed T helper type-2 (Th2) immune responses of the lungs to otherwise innocuous inhaled antigens. Current asthma therapeutics are directed towards the amelioration of downstream consequences of type-2 immune responses (i.e. β-agonists) or broad-spectrum immunosuppression (i.e. corticosteroids). However, few approaches to date have been focused on the primary prevention of immune deviation. Advances in molecular phenotyping reveal heterogeneity within the asthmatic population with multiple endotypes whose varying expression depends on the interplay between numerous environmental factors and the inheritance of a broad range of susceptibility genes. The most common endotype is one described as "type-2-high" (i.e. high levels of interleukin [IL]-13, eosinophilia, and periostin). The identification of multiple endotypes has provided a potential explanation for the observations that therapies directed at typical Th2 cytokines (IL-4, IL-5, and IL-13) and their receptors have often fallen short when they were tested in a diverse group of asthmatic patients without first stratifying based on disease endotype or severity. However, despite the incorporation of endotype-dependent stratification schemes into clinical trial designs, variation in drug responses are still apparent, suggesting that additional genetic/environmental factors may be contributing to the diversity in drug efficacy. Herein, we will review recent advances in our understanding of the complex pathways involved in the initiation and regulation of type-2-mediated immune responses and their modulation by host factors (genetics, metabolic status, and the microbiome). Particular consideration will be given to how this knowledge could pave the way for further refinement of disease endotypes and/or the development of novel therapeutic strategies for the treatment of asthma .

The role of ILC2 in hookworm infection

Hookworm is a major public health concern, yet still relatively little is known about the immunological responses involved in human infection. Animal studies are mainly confined to using the natural rodent helminth Nippostrongylus brasiliensis as this has been proposed as the most accurate model of hookworm infection in the mouse, with both its life cycle and the immune responses it invokes having been extremely well characterized. In this review, we examine the roles that type 2 innate lymphoid cells (ILC2s) play in immunity and host tolerance to hookworm infection, particularly N. brasiliensis. This includes their role in the initiation and regulation of immune responses, as well as in the resolution and limitation of tissue damage required after an infection with a large organism, such as a helminth.

Immune-mediated inflammation in the pathogenesis of emphysema: insights from mouse models

The cellular mechanisms that result in the initiation and progression of emphysema are clearly complex. A growing body of human data combined with discoveries from mouse models utilizing cigarette smoke exposure or protease administration have improved our understanding of emphysema development by implicating specific cell types that may be important for the pathophysiology of chronic obstructive pulmonary disease. The most important aspects of emphysematous damage appear to be oxidative or protease stress and sustained macrophage activation and infiltration of other immune cells leading to epithelial damage and cell death. Despite the identification of these associated processes and cell types in many experimental studies, the reasons why cigarette smoke and other pollutants result in unremitting damage instead of injury resolution are still uncertain. We propose an important role for macrophages in the sequence of events that lead and maintain this chronic tissue pathologic process in emphysema. This model involves chronic activation of macrophage subtypes that precludes proper healing of the lung. Further elucidation of the cross-talk between epithelial cells that release damage-associated signals and the cellular immune effectors that respond to these cues is a critical step in the development of novel therapeutics that can restore proper lung structure and function to those afflicted with emphysema.

Species dependent impact of helminth-derived antigens on human macrophages infected with Mycobacterium tuberculosis: Direct effect on the innate anti-mycobacterial response

Background

In countries with a high prevalence of tuberculosis there is high coincident of helminth infections that might worsen disease outcome. While Mycobacterium tuberculosis (Mtb) gives rise to a pro-inflammatory Th1 response, a Th2 response is typical of helminth infections. A strong Th2 response has been associated with decreased protection against tuberculosis.

Principal findings

We investigated the direct effect of helminth-derived antigens on human macrophages, hypothesizing that helminths would render macrophages less capable of controlling Mtb. Measuring cytokine output, macrophage surface markers with flow cytometry, and assessing bacterial replication and phagosomal maturation revealed that antigens from different species of helminth directly affect macrophage responses to Mtb. Antigens from the tapeworm Hymenolepis diminuta and the nematode Trichuris muris caused an anti-inflammatory response with M2-type polarization, reduced macrophage phagosome maturation and ability to activate T cells, along with increased Mtb burden, especially in T. muris exposed cells which also induced the highest IL-10 production upon co-infection. However, antigens from the trematode Schistosoma mansoni had the opposite effect causing a decrease in IL-10 production, M1-type polarization and increased control of Mtb.

Conclusion

We conclude that, independent of any adaptive immune response, infection with helminth parasites, in a species-specific manner can influence the outcome of tuberculosis by either enhancing or diminishing the bactericidal function of macrophages.

The innate immune system is the first response against invading pathogens like the bacterium Mycobacterium tuberculosis (Mtb) or parasitic worms (helminths). The adaptive immune response takes over after being primed by the innate immune response. Infection with Mycobacterium tuberculosis typically gives rise to a pro-inflammatory T-helper(Th)-1 response while helminths promote a Th2 response which is needed to combat the infection. Co-infection with both of these pathogens could lead to reduced immunity contributing to worsening of tuberculosis due to an increased Th2 response caused by helminths. We found that antigens from different helminth species (a nematode, a cestode and a trematode) caused different responses towards Mtb in macrophages. Depending on the helminth species, the macrophages can be more or less capable of combating Mtb infection and priming the adaptive immune response, which in turn would influence the outcome of tuberculosis. Thus, exposure to helminth antigens, in a species-dependent manner, could lead to a better control of Mtb infection or worsening of tuberculosis.

Metabolic reprogramming & inflammation: Fuelling the host response to pathogens

Successful immune responses to pathogens rely on efficient host innate processes to contain and limit bacterial growth, induce inflammatory response and promote antigen presentation for the development of adaptive immunity. This energy intensive process is regulated through multiple mechanisms including receptor-mediated signaling, control of phago-lysomal fusion events and promotion of bactericidal activities. Inherent macrophage activities therefore are dynamic and are modulated by signals and changes in the environment during infection. So too does the way these cells obtain their energy to adapt to altered homeostasis. It has emerged recently that the pathways employed by immune cells to derive energy from available or preferred nutrients underline the dynamic changes associated with immune activation. In particular, key breakpoints have been identified in the metabolism of glucose and lipids which direct not just how cells derive energy in the form of ATP, but also cellular phenotype and activation status. Much of this comes about through altered flux and accumulation of intermediate metabolites. How these changes in metabolism directly impact on the key processes required for anti-microbial immunity however, is less obvious. Here, we examine the 2 key nutrient utilization pathways employed by innate cells to fuel central energy metabolism and examine how these are altered in response to activation during infection, emphasising how certain metabolic switches or 'reprogramming' impacts anti-microbial processes. By examining carbohydrate and lipid pathways and how the flux of key intermediates intersects with innate immune signaling and the induction of bactericidal activities, we hope to illustrate the importance of these metabolic switches for protective immunity and provide a potential mechanism for how altered metabolic conditions in humans such as diabetes and hyperlipidemia alter the host response to infection.

Tissue-specific contribution of macrophages to wound healing

Macrophages are present in all tissues, either as resident cells or monocyte-derived cells that infiltrate into tissues. The tissue site largely determines the phenotype of tissue-resident cells, which help to maintain tissue homeostasis and act as sentinels of injury. Both tissue resident and recruited macrophages make a substantial contribution to wound healing following injury. In this review, we evaluate how macrophages in two fundamentally distinct tissues, i.e. the lung and the skin, differentially contribute to the process of wound healing. We highlight the commonalities of macrophage functions during repair and contrast them with distinct, tissue-specific functions that macrophages fulfill during the different stages of wound healing.

Alternatively Activated Mononuclear Phagocytes from the Skin Site of Infection and the Impact of IL-4Rα Signalling on CD4+T Cell Survival in Draining Lymph Nodes after Repeated Exposure to Schistosoma mansoni Cercariae

In a murine model of repeated exposure of the skin to infective Schistosoma mansoni cercariae, events leading to the priming of CD4 cells in the skin draining lymph nodes were examined. The dermal exudate cell (DEC) population recovered from repeatedly (4x) exposed skin contained an influx of mononuclear phagocytes comprising three distinct populations according to their differential expression of F4/80 and MHC-II. As determined by gene expression analysis, all three DEC populations (F4/80-MHC-IIhigh, F4/80+MHC-IIhigh, F4/80+MHC-IIint) exhibited major up-regulation of genes associated with alternative activation. The gene encoding RELMα (hallmark of alternatively activated cells) was highly up-regulated in all three DEC populations. However, in 4x infected mice deficient in RELMα, there was no change in the extent of inflammation at the skin infection site compared to 4x infected wild-type cohorts, nor was there a difference in the abundance of different mononuclear phagocyte DEC populations. The absence of RELMα resulted in greater numbers of CD4+ cells in the skin draining lymph nodes (sdLN) of 4x infected mice, although they remained hypo-responsive. Using mice deficient for IL-4Rα, in which alternative activation is compromised, we show that after repeated schistosome infection, levels of regulatory IL-10 in the skin were reduced, accompanied by increased numbers of MHC-IIhigh cells and CD4+ T cells in the skin. There were also increased numbers of CD4+ T cells in the sdLN in the absence of IL-4Rα compared to cells from singly infected mice. Although their ability to proliferate was still compromised, increased cellularity of sdLN from 4x IL-4RαKO mice correlated with reduced expression of Fas/FasL, resulting in decreased apoptosis and cell death but increased numbers of viable CD4+ T cells. This study highlights a mechanism through which IL-4Rα may regulate the immune system through the induction of IL-10 and regulation of Fas/FasL mediated cell death.

In vitro and in vivo evaluation of 2-aminoalkanol and 1,2-alkanediamine derivatives against Strongyloides venezuelensis

Background

Strongyloidiasis is a parasitic disease widely present in tropical and subtropical areas. Strongyloides stercoralis represents the main species that infects human beings. Ivermectin is the current drug of choice; however, issues related with treatment failure in patients with diabetes or infected with T-lymphotropic virus-1 make the identification of new molecules for alternative treatment a priority. In the present study, the activity of sphingosine-related aminoalcohol and diamine were evaluated against Strongyloides venezuelensis third-stage larva (L3) cultures and experimental infections in mice.

Methods

The efficacy of each compound against L3 was assessed using both XTT (2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide) assay and microscopic observation with concentrations ranging from 1 to 350 μM. Cytotoxicity was evaluated using J774.2 macrophage cell line and XTT assay. Lethal concentration 50 (LC₅₀), selectivity index (SI) and structure-activity relationships were established. The activity compounds 4 (2-(ethylamino) hexadecan-1-ol), 6 (2-(butylamino) hexadecan-1-ol), 17 (tert-butyl N-(1-aminododecan-2-yl) carbamate) and 18 (tert-butyl N-(1-aminohexadecan-2-yl) carbamate) were further assessed against experimental S. venezuelensis infections in CD1 mice measuring reductions in the numbers of parthenogenetic females and egg passed in faeces. Mice were infected with 3,000 L3 and treated with 20 mg/kg/day for five days.

Results

In the screening study of 15 aminoalcohols [lauryl (n = 9); palmityl (n = 13); stearyl (n = 15) and alcohol derivatives], the presence of a palmitol chain was associated with the highest efficacy against L3 (LC₅₀ 31.9–39.1 μM). Alkylation of the 2-amino group with medium size fragments as ethyl or n-butyl showed the best larvicidal activity. The dialkylation did not improve efficacy. Aminoalcohols 4 and 6 showed the highest SI (1.5 and 1.6, respectively). With respect to diamine derivative compounds, a chain size of sixteen carbon atoms (palmitoyl chain, n = 13), and the alkylation of the 2-amino group with medium-sized fragments, were associated with the highest lethal activities. The presence of carbamoyl group in diamines 17 and 18 yielded high SI (1.7 and 1.4, respectively). Infected mice treated with aminoalcohol 6 showed reduction in parthenogenetic females (59 %) and eggs in faeces (51 %).

Conclusions

These results support the potentiality of aminoalcohol and diamine sphingosine-related compounds as suitable prototypes for developing new promising drugs against strongyloidiasis.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-016-1648-5) contains supplementary material, which is available to authorized users.

Soluble antigen derived from IV larva of Angiostrongylus cantonensis promotes chitinase-like protein 3 (Chil3) expression induced by interleukin-13

Angiostrongyliasis caused by Angiostrongylus cantonensis (A. cantonensis) is an emerging food-borne parasitic disease, which refers basically to eosinophilic meningitis. Chitinase-like protein 3 (Chil3), a member of chitinase-like protein family which has chemotactic activity for eosinophils, is reported to be highly upregulated in brain of mouse infected with A. cantonensis. The mechanisms of high expression of Chil3 and the association between A. cantonensis and Chil3 are rarely reported. In order to understand the mechanism of high expression of Chil3 in A. cantonensis-infected mouse, we measured the level of Chil3 in RAW 264.7 and BV2 cell lines stimulated with soluble antigen of A. cantonensis by qPCR and ELISA. To explore the role of Chil3 in inflammation caused by A. cantonensis, we extracted and cultured brain mononuclear cells (BMNCs) and detected the eosinophil chemotactic activity of Chil3 using transwell assay and flow cytometer. Furthermore, we treated the infected mice by injection with rmChil3 and then counted the number of larvae in brains of infected mice and treated mice to examine the association between the worm and Chil3. Our results showed the soluble antigen from A. cantonensis could promote the Chil3 expression in macrophage and microglial cell lines induced by interleukin-13. In conclusion, we supposed that high expression of Chil3 enhanced by soluble antigens from A. cantonensis might be the reason of serious eosinophil infiltration in mouse brain after A. cantonensis infection.

Comprehensive Transcriptome Meta-analysis to Characterize Host Immune Responses in Helminth Infections

Helminth infections affect more than a third of the world’s population. Despite very broad phylogenetic differences among helminth parasite species, a systemic Th2 host immune response is typically associated with long-term helminth infections, also known as the “helminth effect”. Many investigations have been carried out to study host gene expression profiles during helminth infections. The objective of this study is to determine if there is a common transcriptomic signature characteristic of the helminth effect across multiple helminth species and tissue types. To this end, we performed a comprehensive meta-analysis of publicly available gene expression datasets. After data processing and adjusting for study-specific effects, we identified ~700 differentially expressed genes that are changed consistently during helminth infections. Functional enrichment analyses indicate that upregulated genes are predominantly involved in various immune functions, including immunomodulation, immune signaling, inflammation, pathogen recognition and antigen presentation. Down-regulated genes are mainly involved in metabolic process, with only a few of them are involved in immune regulation. This common immune gene signature confirms previous observations and indicates that the helminth effect is robust across different parasite species as well as host tissue types. To the best of our knowledge, this study is the first comprehensive meta-analysis of host transcriptome profiles during helminth infections.

Many studies have been conducted to understand the immune modulatory effects in helminth infections. To determine whether there is a common transcriptomic signature characteristic of the helminth effect, we performed a comprehensive meta-analysis of publicly available gene expression datasets. The results revealed a distinct pattern of gene expression that is consistent across multiple helminth species and host tissue types, with upregulated genes dominated by those involved in immune regulation, Th2 immunity and inflammatory responses.

Arginase 1 is an innate lymphoid-cell-intrinsic metabolic checkpoint controlling type 2 inflammation

Group 2 innate lymphoid cells (ILC2s) regulate tissue inflammation and repair following activation by cell-extrinsic factors including host-derived cytokines. However, the cell-intrinsic metabolic pathways that control ILC2 function are undefined. Here we demonstrate that expression of the enzyme Arginase 1 (Arg1) is a conserved trait of murine and human ILC2s during acute or chronic lung inflammation. Deletion of murine ILC-intrinsic Arg1 abrogated type 2 lung inflammation by restraining ILC2 proliferation and dampening cytokine production. Mechanistically, inhibition of Arg1 enzymatic activity disrupted multiple components of ILC2 metabolic programming by altering arginine catabolism, impairing polyamine biosynthesis and reducing aerobic glycolysis. These data identify Arg1 as a key regulator of ILC2 bioenergetics, controlling proliferative capacity and pro-inflammatory functions that promote type 2 inflammation.

Recruited monocytes modulate malaria-induced lung injury through CD36-mediated clearance of sequestered infected erythrocytes

Pulmonary complications occur in a significant percentage of adults and children during the course of severe malaria. The cellular and molecular innate immune mechanisms that limit the extent of pulmonary inflammation and preserve lung function during severe Plasmodium infections remain unclear. In particular, the contributions to pulmonary complications by parasitized erythrocyte sequestration and subsequent clearance from the lung microvasculature by immune cells have not been clearly defined. We used the Plasmodium berghei ANKA-C57BL/6 mouse model of severe malaria to investigate the mechanisms governing the nature and extent of malaria-associated lung injury. We have demonstrated that sequestration of infected erythrocytes on postcapillary endothelial surfaces results in acute lung injury and the rapid recruitment of CCR2(+)CD11b(+)Ly6C(hi) monocytes from the circulation. These recruited cells remain in the lungs as monocyte-derived macrophages and are instrumental in the phagocytic clearance of adherent Plasmodium berghei-infected erythrocytes. In contrast, alveolar macrophages do not play a significant role in the clearance of malaria-infected cells. Furthermore, the results obtained from Ccr2(-/-), Cd36(-/-), and CD36 bone marrow chimeric mice showed that sequestration in the absence of CD36-mediated phagocytic clearance by monocytes leads to exaggerated lung pathologic features. In summary, our data indicate that the intensity of malaria-induced lung pathologic features is proportional to the steady-state levels of Plasmodium-infected erythrocytes adhering to the pulmonary vasculature. Moreover, the present work has defined a major role of recruited monocytes in clearing infected erythrocytes from the pulmonary interstitium, thus minimizing lung damage.

Myeloid expression of the AP-1 transcription factor JUNB modulates outcomes of type 1 and type 2 parasitic infections

Activation of macrophages is a key step in the initiation of immune responses, but the transcriptional mechanisms governing macrophage activation during infection are not fully understood. It was recently shown that the AP-1 family transcription factor JUNB positively regulates macrophage activation in response to Toll-like receptor agonists that promote classical or M1 polarization, as well as to the cytokine interleukin-4 (IL-4), which elicits an alternatively activated or M2 phenotype. However, a role for JUNB in macrophage activation has never been demonstrated in vivo. Here, to dissect the role of JUNB in macrophage activation in a physiological setting, mice lacking JUNB specifically in myeloid cells were tested in two infection models: experimental cerebral malaria, which elicits a pathological type 1 immune response, and helminth infection, in which type 2 responses are protective. Myeloid-restricted deletion of Junb reduced type 1 immune activation, which was associated with reduced cerebral pathology and improved survival during infection with Plasmodium berghei. Myeloid JUNB deficiency also compromised type 2 activation during infection with the hookworm Nippostrongylus brasiliensis, leading to diminished cytokine production and eosinophil recruitment and increased parasite burden. These results demonstrate that JUNB in myeloid cells shapes host responses and outcomes during type 1 and type 2 infections.

Metabolic reprogramming in macrophages and dendritic cells in innate immunity

Activation of macrophages and dendritic cells (DCs) by pro-inflammatory stimuli causes them to undergo a metabolic switch towards glycolysis and away from oxidative phosphorylation (OXPHOS), similar to the Warburg effect in tumors. However, it is only recently that the mechanisms responsible for this metabolic reprogramming have been elucidated in more detail. The transcription factor hypoxia-inducible factor-1α (HIF-1α) plays an important role under conditions of both hypoxia and normoxia. The withdrawal of citrate from the tricarboxylic acid (TCA) cycle has been shown to be critical for lipid biosynthesis in both macrophages and DCs. Interference with this process actually abolishes the ability of DCs to activate T cells. Another TCA cycle intermediate, succinate, activates HIF-1α and promotes inflammatory gene expression. These new insights are providing us with a deeper understanding of the role of metabolic reprogramming in innate immunity.

Macrophage-derived human resistin is induced in multiple helminth infections and promotes inflammatory monocytes and increased parasite burden

Parasitic helminth infections can be associated with lifelong morbidity such as immune-mediated organ failure. A better understanding of the host immune response to helminths could provide new avenues to promote parasite clearance and/or alleviate infection-associated morbidity. Murine resistin-like molecules (RELM) exhibit pleiotropic functions following helminth infection including modulating the host immune response; however, the relevance of human RELM proteins in helminth infection is unknown. To examine the function of human resistin (hResistin), we utilized transgenic mice expressing the human resistin gene (hRetnTg⁺). Following infection with the helminth Nippostrongylus brasiliensis (Nb), hResistin expression was significantly upregulated in infected tissue. Compared to control hRetnTg⁻ mice, hRetnTg⁺ mice suffered from exacerbated Nb-induced inflammation characterized by weight loss and increased infiltration of inflammatory monocytes in the lung, along with elevated Nb egg burdens and delayed parasite expulsion. Genome-wide transcriptional profiling of the infected tissue revealed that hResistin promoted expression of proinflammatory cytokines and genes downstream of toll-like receptor signaling. Moreover, hResistin preferentially bound lung monocytes, and exogenous treatment of mice with recombinant hResistin promoted monocyte recruitment and proinflammatory cytokine expression. In human studies, increased serum resistin was associated with higher parasite load in individuals infected with soil-transmitted helminths or filarial nematode Wuchereria bancrofti, and was positively correlated with proinflammatory cytokines. Together, these studies identify human resistin as a detrimental factor induced by multiple helminth infections, where it promotes proinflammatory cytokines and impedes parasite clearance. Targeting the resistin/proinflammatory cytokine immune axis may provide new diagnostic or treatment strategies for helminth infection and associated immune-mediated pathology.

Parasitic helminths, which infect an estimated two billion people worldwide, represent a significant global public health problem. Infection is associated with life-long morbidity including growth retardation and organ failure. Despite these debilitating conditions, there are currently no successful vaccines against helminths. Further, great variability in the host immune response to helminths exists, with the ability of some individuals to develop immunity, while others are susceptible when re-exposed or maintain life-long chronic infections. Identifying new factors that are differentially expressed in immune versus susceptible individuals could provide new targeting strategies for diagnosis or treatment of helminth infection. Here, we identify an important immunoregulatory function for human resistin in helminth infection. Employing transgenic mice in which the human resistin gene was inserted, we show that human resistin is induced by infection with the helminth Nippostrongylus brasiliensis, where it promotes excessive inflammation and impedes parasite killing. Moreover, analysis of clinical samples from two cohorts of individuals infected with filarial nematodes or soil-transmitted helminths revealed increased resistin and serum proinflammatory cytokines compared to putatively immune individuals. Together, these studies suggest that human resistin is a detrimental cytokine that is expressed in multiple helminth infections, mediates pathogenic inflammation, and delays parasite clearance.

Helminths in the lungs

Parasitic helminths infect well over one billion people and typically cause chronic and recurrent infections that exert a considerable toll on human health and productivity. A significant number of important intestinal- and tissue-dwelling helminth parasites have evolved a scripted migration through select organ systems. Of specific interest here are the helminth parasites that interact with respiratory tissues and the pulmonary immune system. This review will consider the nature of the interactions between helminth parasites and the lung environment, as well as the consequences of these interactions on the evolution of parasitism and host immunity.

Chitinase-like proteins promote IL-17-mediated neutrophilia in a tradeoff between nematode killing and host damage

Enzymatically inactive chitinase-like proteins (CLPs) such as BRP-39, Ym1 and Ym2 are established markers of immune activation and pathology, yet their functions are essentially unknown. We found that Ym1 and Ym2 induced the accumulation of neutrophils through the expansion of γδ T cell populations that produced interleukin 17 (IL-17). While BRP-39 did not influence neutrophilia, it was required for IL-17 production in γδ T cells, which suggested that regulation of IL-17 is an inherent feature of mouse CLPs. Analysis of a nematode infection model, in which the parasite migrates through the lungs, revealed that the IL-17 and neutrophilic inflammation induced by Ym1 limited parasite survival but at the cost of enhanced lung injury. Our studies describe effector functions of CLPs consistent with innate host defense traits of the chitinase family.

Trichinella spiralis: killing of newborn larvae by lung cells

The migratory stage of Trichinella spiralis, the newborn larva (NBL), travels along the pulmonary microvascular system on its way to the skeletal muscle cells. The present work studies the capability of lung cells to kill NBL. For this purpose, in vitro cytotoxicity assays were performed using NBL, lung cell suspensions from Wistar rats, rat anti-NBL surface sera, and fresh serum as complement source. The cytotoxic activity of lung cells from rats infected on day 6 p.i. was compared with that from noninfected rats. Two and 20 h-old NBL (NBL2 and NBL20) were used as they had shown to exhibit different surface antigens altering their biological activity. Sera antibodies were analyzed by indirect immunofluorescence assay, and cell populations used in each assay were characterized by histological staining. The role of IgE in the cytotoxic attack against NBL was analyzed using heated serum. The FcεRI expression on cell suspensions was examined by flow cytometry. Results showed that lung cells were capable of killing NBL by antibody-dependent cell-mediated cytotoxicity (ADCC). Lung cells from infected animals yielded the highest mortality percentages of NBL, with NBL20 being the most susceptible to such attack. IgE yielded a critical role in the cytotoxic attack. Regarding the analysis of cell suspensions, cells from infected rats showed an increase in the percentage of eosinophils, neutrophils, and the number of cells expressing the FcεRI receptor. We conclude that lung cells are capable of killing NBL in the presence of specific antibodies, supporting the idea that the lung is one of the sites where the NBL death occurs due to ADCC.

Gene expression in whole lung and pulmonary macrophages reflects the dynamic pathology associated with airway surface dehydration

Background

Defects in airway mucosal defense, including decreased mucus clearance, contribute to the pathogenesis of human chronic obstructive pulmonary diseases. Scnn1b-Tg mice, which exhibit chronic airway surface dehydration from birth, can be used as a model to study the pathogenesis of muco-obstructive lung disease across developmental stages. To identify molecular signatures associated with obstructive lung disease in this model, gene expression analyses were performed on whole lung and purified lung macrophages collected from Scnn1b-Tg and wild-type (WT) littermates at four pathologically relevant time points. Macrophage gene expression at 6 weeks was evaluated in mice from a germ-free environment to understand the contribution of microbes to disease development.

Results

Development- and disease-specific shifts in gene expression related to Scnn1b over-expression were revealed in longitudinal analyses. While the total number of transgene-related differentially expressed genes producing robust signals was relatively small in whole lung (n = 84), Gene Set Enrichment Analysis (GSEA) revealed significantly perturbed biological pathways and interactions between normal lung development and disease initiation/progression. Purified lung macrophages from Scnn1b-Tg mice exhibited numerous robust and dynamic gene expression changes. The expression levels of Classically-activated (M1) macrophage signatures were significantly altered at post-natal day (PND) 3 when Scnn1b-Tg mice lung exhibit spontaneous bacterial infections, while alternatively-activated (M2) macrophage signatures were more prominent by PND 42, producing a mixed M1-M2 activation profile. While differentially-regulated, inflammation-related genes were consistently identified in both tissues in Scnn1b-Tg mice, there was little overlap between tissues or across time, highlighting time- and tissue-specific responses. Macrophages purified from adult germ-free Scnn1b-Tg mice exhibited signatures remarkably similar to non-germ-free counterparts, indicating that the late-phase macrophage activation profile was not microbe-dependent.

Conclusions

Whole lung and pulmonary macrophages respond independently and dynamically to local stresses associated with airway mucus stasis. Disease-specific responses interact with normal developmental processes, influencing the final state of disease in this model. The robust signatures observed in Scnn1b-Tg lung macrophages highlight their critical role in disease pathogenesis. These studies emphasize the importance of region-, cell-type-, and time-dependent analyses to fully dissect the natural history of disease and the consequences of disease on normal lung development.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-726) contains supplementary material, which is available to authorized users.