Eosinophils are important for protection, immunoregulation and pathology during infection with nematode microfilariae

Th2-biased immune responses to body migrating Ascaris larvae in primary infection are associated with pathology but not protection

Helminth infections lead to an overdispersion of the parasites in humans as well as in animals. We asked whether early immune responses against migrating Ascaris larvae are responsible for the unequal distribution of worms in natural host populations and thus investigated a susceptible versus a resistant mouse strain. In mice, the roundworm larvae develop until the lung stage and thus early anti-Ascaris immune responses against the migrating larvae in the liver and lung can be deciphered. Our data show that susceptible C57BL/6 mice respond to Ascaris larval migration significantly stronger compared to resistant CBA mice and the anti-parasite reactivity is associated with pathology. Increased eosinophil recruitment was detected in the liver and lungs, but also in the spleen and peritoneal cavity of susceptible mice on day 8 post infection compared to resistant mice. In serum, eosinophil peroxidase levels were significantly higher only in the susceptible mice, indicating functional activity of the recruited eosinophils. This effect was associated with an increased IL-5/IL-13 production by innate lymphoid cells and CD4+ T cells and a pronounced type 2 macrophage polarization in the lungs of susceptible mice. Furthermore, a comparison of wildtype BALB/c and eosinophil-deficient dblGATA-1 BALB/c mice showed that eosinophils were not essential for the early control of migrating Ascaris larvae. In conclusion, in primary infection, a strong local and systemic type 2 immune response during hepato-tracheal helminth larval migration is associated with pathology rather than protection.

Epithelial IL5RA promotes epithelial-mesenchymal transition in pulmonary fibrosis via Jak2/STAT3 cascade

Pulmonary fibrosis is a progressive and debilitating lung disease characterized by the excessive accumulation of extracellular matrix (ECM) components within the lung parenchyma. However, the underlying mechanism remains largely elusive, and the treatment options available for pulmonary fibrosis are limited. Interleukin 5 receptor, alpha (IL5RA) is a well-established regulator of eosinophil activation, involved in eosinophil-mediated anti-parasitic activities and allergic reactions. Recent studies have indicated additional roles of IL5RA in lung epithelium and fibroblasts. Nevertheless, its involvement in pulmonary fibrosis remains unclear. In present study, we employed single-cell analyses alongside molecular and cellular assays to unveil the expression of IL5RA in lung epithelial cells. Moreover, using both in vitro and in vivo models, we demonstrated a notable upregulation of epithelial IL5RA during the progression of pulmonary fibrosis. This upregulated IL5RA expression subsequently promotes epithelial-mesenchymal transition (EMT), leading to the generation of mesenchymal phenotype with augmented capability for ECM production. Importantly, our findings uncovered that the pro-fibrotic function of IL5RA is mediated by Jak2/STAT3 signaling cascades. Inhibiting IL5RA has the potential to deactivate Jak2/STAT3 and suppress the downstream EMT process and ECM production, thereby offering a promising therapeutic strategy for pulmonary fibrosis.

Eosinophils-from cradle to grave: An EAACI task force paper on new molecular insights and clinical functions of eosinophils and the clinical effects of targeted eosinophil depletion

Over the past years, eosinophils have become a focus of scientific interest, especially in the context of their recently uncovered functions (e.g. antiviral, anti-inflammatory, regulatory). These versatile cells display both beneficial and detrimental activities under various physiological and pathological conditions. Eosinophils are involved in the pathogenesis of many diseases which can be classified into primary (clonal) and secondary (reactive) disorders and idiopathic (hyper)eosinophilic syndromes. Depending on the biological specimen, the eosinophil count in different body compartments may serve as a biomarker reflecting the underlying pathophysiology and/or activity of distinct diseases and as a therapy-driving (predictive) and monitoring tool. Personalized selection of an appropriate therapeutic strategy directly or indirectly targeting the increased number and/or activity of eosinophils should be based on the understanding of eosinophil homeostasis including their interactions with other immune and non-immune cells within different body compartments. Hence, restoring as well as maintaining homeostasis within an individual's eosinophil pool is a goal of both specific and non-specific eosinophil-targeting therapies. Despite the overall favourable safety profile of the currently available anti-eosinophil biologics, the effect of eosinophil depletion should be monitored from the perspective of possible unwanted consequences.

The Relationship of Parasite Allergens to Allergic Diseases

PURPOSE OF REVIEW

Helminth infections modify the natural history of allergic diseases, by either decreasing or increasing their symptoms. Several helminth components are involved in the increasing of the allergic response and symptoms, overcoming the concomitant immunosuppression of helminthiases. However, the role of individual IgE-binding molecules in this process remains to be defined.

RECENT FINDINGS

We updated the list of helminth allergens and IgE-binding molecules, their effects on asthma presentation, and their impact on allergy diagnosis. Data from genetic and epigenetic studies of ascariasis are analyzed. A new species-specific A. lumbricoides allergen has been discovered, with potential use in molecular diagnosis. Most helminth IgE-binding components are not officially classified as allergens in the WHO/IUIS database, although there is evidence of their influence increasing allergic manifestations. Further immunological characterization of these components is needed to better understand their mechanisms of action and evaluate the ways in which they can influence the diagnosis of allergy.

Eosinophil: An innate immune cell with anti-filarial vaccine and biomarker potential

Background

Filarial infections continue to pose a great challenge in endemic countries. One of the central goals in the fight against human filarial infections is the development of strategies that will lead to the inhibition of microfilariae (mf) transmission. Keeping mf under a certain threshold within endemic populations will stop transmission and eliminate the infection.

Method

A narrative review was carried out to identify the possibilities and limitations of exploring the use of eosinophil responses as an anti-filarial vaccine, and biomarker for the detection of filarial infections. An extensive literature search was performed in online scientific databases including PubMed Central, PubMed, BioMed Central, with the use of predefined search terms.

Results

A better understanding of the parasite-host interactions will lead to the development of improved and better treatment or vaccine strategies that could eliminate filariasis as soon as possible. Highlighted in this review is the explorative use of eosinophil-producing CLC/Galectin-10 as a potential biomarker for filarial infections. Also discussed are some genes, and pathways involved in eosinophil recruitments that could be explored for anti-filarial vaccine development.

Conclusion

In this short communication, we discuss how eosinophil-regulated genes, pathways, and networks could be critical in providing more information on how reliably a front-line immune player could be exploited for anti-filarial vaccine development and early infection biomarker.

How to train your myeloid cells: a way forward for helminth vaccines?

Soil-transmitted helminths affect approximately 1.5 billion people worldwide. However, as no vaccine is currently available for humans, the current strategy for elimination as a public health problem relies on preventive chemotherapy. Despite more than 20 years of intense research effort, the development of human helminth vaccines (HHVs) has not yet come to fruition. Current vaccine development focuses on peptide antigens that trigger strong humoral immunity, with the goal of generating neutralizing antibodies against key parasite molecules. Notably, this approach aims to reduce the pathology of infection, not worm burden, with only partial protection observed in laboratory models. In addition to the typical translational hurdles that vaccines struggle to overcome, HHVs face several challenges (1): helminth infections have been associated with poor vaccine responses in endemic countries, probably due to the strong immunomodulation caused by these parasites, and (2) the target population displays pre-existing type 2 immune responses to helminth products, increasing the likelihood of adverse events such as allergy or anaphylaxis. We argue that such traditional vaccines are unlikely to be successful on their own and that, based on laboratory models, mucosal and cellular-based vaccines could be a way to move forward in the fight against helminth infection. Here, we review the evidence for the role of innate immune cells, specifically the myeloid compartment, in controlling helminth infections. We explore how the parasite may reprogram myeloid cells to avoid killing, notably using excretory/secretory (ES) proteins and extracellular vesicles (EVs). Finally, learning from the field of tuberculosis, we will discuss how anti-helminth innate memory could be harnessed in a mucosal-trained immunity-based vaccine.

Effects of Cannabidiol on Innate Immunity: Experimental Evidence and Clinical Relevance

Cannabidiol (CBD) is the main non-psychotropic cannabinoid derived from cannabis (Cannabis sativa L., fam. Cannabaceae). CBD has received approval by the Food and Drug Administration (FDA) and European Medicines Agency (EMA) for the treatment of seizures associated with Lennox-Gastaut syndrome or Dravet syndrome. However, CBD also has prominent anti-inflammatory and immunomodulatory effects; evidence exists that it could be beneficial in chronic inflammation, and even in acute inflammatory conditions, such as those due to SARS-CoV-2 infection. In this work, we review available evidence concerning CBD's effects on the modulation of innate immunity. Despite the lack so far of clinical studies, extensive preclinical evidence in different models, including mice, rats, guinea pigs, and even ex vivo experiments on cells from human healthy subjects, shows that CBD exerts a wide range of inhibitory effects by decreasing cytokine production and tissue infiltration, and acting on a variety of other inflammation-related functions in several innate immune cells. Clinical studies are now warranted to establish the therapeutic role of CBD in diseases with a strong inflammatory component, such as multiple sclerosis and other autoimmune diseases, cancer, asthma, and cardiovascular diseases.

Living without eosinophils: evidence from mouse and man

The enduring view of eosinophils, as immune effector cells whose primary function is host defence against infection by helminths and other microbial pathogens, sets the stage for a fundamental question regarding the safety of therapeutic eosinophil depletion. If eosinophils are significantly reduced or altogether depleted in an effort to alleviate the negative effects of tissue eosinophilia and eosinophilic inflammation in conditions such as asthma, COPD, chronic rhinosinusitis with nasal polyps, eosinophilic granulomatosis with polyangiitis and hypereosinophilic syndrome, would these patients become susceptible to infection or another illness? Development of mouse models in which the eosinophil lineage has been ablated, observations in patients naturally lacking eosinophils and data from studies of eosinophil-depleting medical therapies indicate that the absence of eosinophils is not detrimental to health. The evidence available to date, as presented in this review, supports the conclusion that even if certain homeostatic roles for the eosinophil may be demonstrable in controlled animal models and human in vitro settings, the evolution of the human species appears to have provided sufficient immune redundancy such that one may be hale and hearty without eosinophils.

A Case of Tropical Pulmonary Eosinophilia With Incomplete Response to Diethylcarbamazine Therapy

Tropical pulmonary eosinophilia (TPE) is a specific pulmonary manifestation of lymphatic filariasis. There is overwhelming infiltration of eosinophils in the lung parenchyma in response to microfilaria. The characteristic features include paroxysmal respiratory symptoms, strikingly high blood eosinophil count, elevated level of immunoglobulin (Ig) E along with high titer of anti-filarial antibody. Treatment with diethylcarbamazine (DEC) has an excellent favorable response. However, recovery may often be incomplete. We present a case of a 36-year-old man with TPE who had complete symptomatic improvement after a three-week course of DEC, but only a partial response in radiological and pulmonary function abnormalities.

Unbalanced Arginine pathway and altered maturation of pleural macrophages in Th2-deficient mice during Litomosoides sigmodontis filarial infection

Filarial parasites are tissue dwelling worms transmitted by hematophagous vectors. Understanding the mechanisms regulating microfilariae (the parasite offspring) development is a prerequisite for controlling transmission in filarial infections. Th2 immune responses are key for building efficient anti-parasite responses but have been shown to also lead to detrimental tissue damage in the presence of microfilariae. Litomosoides sigmodontis, a rodent filaria residing in the pleural cavity was therefore used to characterize pleuropulmonary pathology and associated immune responses in wild-type and Th2 deficient mice. Wild-type and Th2-deficient mice (Il-4rα-/-/Il-5-/- ) were infected with L. sigmodontis and parasite outcome was analyzed during the patent phase (when microfilariae are in the general circulation). Pleuropulmonary manifestations were investigated and pleural and bronchoalveolar cells were characterized by RNA analysis, imaging and/or flow cytometry focusing on macrophages. Il-4rα-/-/Il-5-/- mice were hypermicrofilaremic and showed an enhanced filarial survival but also displayed a drastic reduction of microfilaria-driven pleural cavity pathologies. In parallel, pleural macrophages from Il-4rα-/-/Il-5-/- mice lacked expression of prototypical alternative activation markers RELMα and Chil3 and showed an altered balance of some markers of the arginine metabolic pathway. In addition, monocytes-derived F4/80intermediate macrophages from infected Il-4rα-/-/Il-5-/- mice failed to mature into resident F4/80high large macrophages. Altogether these data emphasize that the presence of both microfilariae and IL-4R/IL-5 signaling are critical in the development of the pathology and in the phenotype of macrophages. In Il-4rα-/-/Il-5-/- mice, the balance is in favor of parasite development while limiting the pathology associated with the host immune response.

Nitric oxide contributes to liver inflammation and parasitic burden control in Ascaris suum infection

BACKGROUND

Human ascariasis is one of the most prevalent neglected tropical diseases worldwide. The immune response during human ascariasis is characterized by Th2 polarization and a mixed Th2/Th17 response during the pathogenesis of experimental larval ascariasis. Cytokines and other pro-inflammatory mediators, such as nitric oxide (NO), are involved in helminthic infections. However, the role of NO in ascariasis remains unclear.

OBJECTIVES

Given the importance of NO in inflammation, we aimed to determine the immunological and histopathological alterations in the livers of C57BL/6 iNOS^-/- mice during A. suum infection.

METHODS

In this study, parasitic load was evaluated in the livers of wild type C57BL/6 and C57BL/6 iNOS^-/- mice infected with A. suum. Histopathological and morphometric analyses and analysis of serum cytokines via Cytometric Bead Array were performed, and the activity of eosinophil peroxidase and myeloperoxidase of neutrophils in the tissues were determined.

RESULTS

The results showed that NO is important for controlling parasitic load during infection by A. suum. C57BL/6iNOS^-/- mice showed reduced inflammatory processes and less tissue damage during liver larval migration of A. suum, which is associated with a reduction in serum levels of pro-inflammatory cytokines.

CONCLUSIONS

We demonstrated that NO is a crucial inflammatory molecule during Ascaris sp. infection and controls the establishment of the parasite and the development of the host immune response in the liver.

Localization and RNA Interference-Driven Inhibition of a Brugia malayi-Encoded Interleukin-5 Receptor Binding Protein

A molecule we termed Brugia malayi IL-5 receptor (IL-5R) binding protein (BmIL5Rbp; also known as Bm8757) was identified from B. malayi filarial worms and found to inhibit human interleukin-5 (IL-5) binding to its human receptor competitively. After the expression and purification of a recombinant BmIL5Rbp and generation of BmIL5Rbp-specific rabbit antibody, we localized the molecule on B. malayi worms through immunohistochemistry and immunoelectron microscopy. RNA interference (RNAi) was used to inhibit BmIL5Rbp mRNA and protein production. BmIL5Rbp was shown to localize to the cuticle of Brugia malayi and to be released in its excretory/secretory products. RNAi inhibited BmIL5Rbp mRNA production by 33%, reduced the surface protein expression by ~50%, and suppressed the release of BmIL5Rbp in the excretory/secretory products. RNAi has been used successfully to knock down the mRNA and protein expression of BmIL5Rbp in the early larval stages of B. malayi and provided a proof of principle for the local inhibition of the human IL-5R. These findings provide evidence that a parasite-encoded IL-5R antagonist may locally inhibit a vital host innate immune activation of IL-5 on eosinophils.

NKp46+ natural killer cells develop an activated/memory-like phenotype and contribute to innate immunity against experimental filarial infection

Lymphatic filariasis and onchocerciasis are major neglected tropical diseases affecting over 90 million people worldwide with painful and profoundly disfiguring pathologies (such as lymphoedema or blindness). Type 2 inflammation is a hallmark of filarial nematode tissue infection and is implicated both in eosinophil dependent immunity and lymphatic or ocular immunopathologies. Type-2 innate lymphoid cells (ILC2) are known to play an important role in the initiation of type 2 inflammation in helminth infection. We therefore tracked comparative IL-12Rβ2⁺ ILC1, ST2⁺ ILC2 and NKp46⁺ natural killer (NK) innate lymphoid cell population expansions during Brugia malayi experimental peritoneal filarial infections using either immunocompetent or immunodeficient mice. In immunocompetent BALB/c animals, NKp46⁺ NK cells rapidly expanded representing over 90% of the ILC population in the first week of infection, whereas, surprisingly, ST2⁺ ILC2 failed to expand. NKp46⁺ NK cell expansions were confirmed in RAG2 deficient mice lacking adaptive immunity. Ablation of the NKp46⁺ NK cell compartment in RAG2 common gamma chain (gc) mice led to increased susceptibility to chronic adult B. malayi infection. This data was recapitulated using an Onchocerca ochengi male worm peritoneal implant model. When NKp46⁺ NK cells were depleted in RAG2 deficient mice using anti-NKp46 or asialo GM1 antibody injections over the first five weeks of B. malayi infection, susceptibility to adult B. malayi infection was significantly increased by 2-3 fold with concomitant impairment in eosinophil or neutrophil recruitments. Finally, we demonstrate that in RAG2 deficient mice, drug clearance of a primary adult B. malayi infection followed by challenge infection leads to resistance against early larval B. malayi establishment. This innate resistance is associated with bolstered NK and eosinophils whereby NKp46⁺ NK cells express markers of memory-like/enhanced activation (increased expression of interferon gamma and Ly6C). Our data promotes a novel functional role for NKp46⁺ NK cells in immunoprotection against experimental primary and secondary filarial infection which can proceed in the absence of adaptive immune regulation.

Advances in preclinical platforms of Loa loa for filarial neglected tropical disease drug and diagnostics research

The tropical disease, loiasis, caused by the filarial parasite, Loa, has gained prominence in global public health as a cause of excess mortality and a barrier to the elimination of the related prioritized neglected tropical diseases (NTDs), lymphatic filariasis and onchocerciasis, within Central Africa. There are no effective drug cures or vaccines available to treat loiasis safely. Here we review recent advances in loiasis preclinical platform technologies, including novel in vitro culturing systems, animal models and innovations in experimental infections of the L. loa vector, Chrysops, that have facilitated access to all L. loa filarial life-cycle stages. We detail applications of these new model systems in anti-filarial drug screening, diagnostic development, immunology, and pathophysiology research. Finally, we provide an overview of how loiasis preclinical platforms may be further utilized in translational medicine applications to support the development of much needed new interventions against filarial NTDs.

Eosinophils participate in modulation of liver immune response and tissue damage induced by Schistosoma mansoni infection in mice

The severity of chronic schistosomiasis has been mainly associated with the intensity and extension of the inflammatory response induced by egg-secreted antigens in the host tissue, especially in the liver and intestine. During acute schistosomiasis, eosinophils account for approximately 50% of the cells that compose the liver granulomas; however, the role of this cell-type in the pathology of schistosomiasis remains controversial. In the current study, we compared the parasite burden and liver immunopathological changes during experimental schistosomiasis in wild-type (WT) BALB/c mice and BALB/c mice selectively deficient for the differentiation of eosinophils (ΔdblGATA). Our data demonstrated that the absence of eosinophil differentiation did not alter the S. mansoni load or the liver retention of parasite eggs; however, there were significant changes in the liver immune response profile and tissue damage. S. mansoni infection in ΔdblGATA mice resulted in significantly lower liver concentrations of IL-5, IL-13, IL-33, IL-17, IL-10, and TGF-β and higher concentrations of IFN-γ and TNF-α, as compared to WT mice. The changes in liver immune response observed in infected ΔdblGATA mice were accompanied by lower collagen deposition, but higher liver damage and larger granulomas. Moreover, the absence of eosinophils resulted in a higher mortality rate in mice infected with a high parasite load. Therefore, the data indicated that eosinophils participate in the establishment and/or amplification of liver Th-2 and regulatory response induced by S. mansoni, which is necessary for the balance between liver damage and fibrosis, which in turn is essential for modulating disease severity.

Eosinophils and helminth infection: protective or pathogenic?

Since the earliest descriptions of this enigmatic cell, eosinophils have been implicated in both protective and pathogenic immune responses to helminth infection. Nevertheless, despite substantial data from in vitro studies, human infections, and animal models, their precise role in helminth infection remains incompletely understood. This is due to a number of factors, including the heterogeneity of the many parasites included in the designation "helminth," the complexity and redundancy in the host immune response to helminths, and the pleiotropic functions of eosinophils themselves. This review examines the consequences of helminth-associated eosinophilia in the context of protective immunity, pathogenesis, and immunoregulation.

Intestinal eosinophils: multifaceted roles in tissue homeostasis and disease

Intestinal eosinophils are largely considered to be one of the central immune effector cells during helminth infection and disorders such as eosinophilic oesophagitis and food allergies. Given the abundance of these cells present in the gastrointestinal tract at homeostasis, emerging studies now reveal novel roles for eosinophils in the development and regulation of immunity, and during tissue repair. In addition, the identification of distinct eosinophil subsets indicates that we must consider the heterogeneity of these cells and how they differentially participate in mucosal immunity at steady state and during disease. Here, we summarise the literature on intestinal eosinophils, and how they contribute to mucosal homeostasis through immune regulation and interactions with the microbiome. We then explore the divergent roles of eosinophils in the context of eosinophilic gastrointestinal disorders and during helminth infection, whereby we discuss key observations and differences that have emerged from animal models and human studies. Lastly, we consider the possible interactions of eosinophils with the enteric nervous system, and how this represents an exciting area for future research which may inform future therapeutic targets.

Eosinophils in the Tumor Microenvironment

Eosinophils are rare blood-circulating and tissue-infiltrating immune cells studied for decades in the context of allergic diseases and parasitic infections. Eosinophils can secrete a wide array of soluble mediators and effector molecules, with potential immunoregulatory activities in the tumor microenvironment (TME). These findings imply that these cells may play a role in cancer immunity. Despite these cells were known to infiltrate tumors since many years ago, their role in TME is gaining attention only recently. In this chapter, we will review the main biological functions of eosinophils that can be relevant within the TME. We will discuss how these cells may undergo phenotypic changes acquiring pro- or antitumoricidal properties according to the surrounding stimuli. Moreover, we will analyze canonical (i.e., degranulation) and unconventional mechanisms (i.e., DNA traps, exosome secretion) employed by eosinophils in inflammatory contexts, which can be relevant for tumor immune responses. Finally, we will review the available preclinical models that could be employed for the study of the role in vivo of eosinophils in cancer.

Microfilaria-dependent thoracic pathology associated with eosinophilic and fibrotic polyps in filaria-infected rodents

BACKGROUND

Pulmonary manifestations are regularly reported in both human and animal filariasis. In human filariasis, the main known lung manifestations are the tropical pulmonary eosinophilia syndrome. Its duration and severity are correlated with the presence of microfilariae. Litomosoides sigmodontis is a filarial parasite residing in the pleural cavity of rodents. This model is widely used to understand the immune mechanisms that are established during infection and for the screening of therapeutic molecules. Some pulmonary manifestations during the patent phase of infection with L. sigmodontis have been described in different rodent hosts more or less permissive to infection.

METHODS

Here, the permissive Mongolian gerbil (Meriones unguiculatus) was infected with L. sigmodontis. Prevalence and density of microfilariae and adult parasites were evaluated. Lungs were analyzed for pathological signatures using immunohistochemistry and 3D imaging techniques (two-photon and light sheet microscopy).

RESULTS

Microfilaremia in gerbils was correlated with parasite load, as amicrofilaremic individuals had fewer parasites in their pleural cavities. Fibrotic polypoid structures were observed on both pleurae of infected gerbils. Polyps were of variable size and developed from the visceral mesothelium over the entire pleura. The larger polyps were vascularized and strongly infiltrated by immune cells such as eosinophils, macrophages or lymphocytes. The formation of these structures was induced by the presence of adult filariae since small and rare polyps were observed before patency, but they were exacerbated by the presence of gravid females and microfilariae.

CONCLUSIONS

Altogether, these data emphasize the role of host-specific factors in the pathogenesis of filarial infections.

Eosinophils Control Liver Damage by Modulating Immune Responses Against Fasciola hepatica

Eosinophils are granulocytes that participate in the defense against helminth parasites and in hypersensitivity reactions. More recently, eosinophils were shown to have other immunomodulatory functions, such as tissue reparation, metabolism regulation, and suppression of Th1 and Th17 immune responses. In the context of parasitic helminth infections, eosinophils have a controversial role, as they can be beneficial or detrimental for the host. In this work, we investigate the role of eosinophils in an experimental infection in mice with the trematode parasite Fasciola hepatica, which causes substantial economical losses around the world due to the infection of livestock. We demonstrate that eosinophils are recruited to the peritoneal cavity and liver from F. hepatica-infected mice and this recruitment is associated with increased levels of CCL11, TSLP, and IL-5. Moreover, the characterization of peritoneal and hepatic eosinophils from F. hepatica-infected mice showed that they express distinctive molecules of activation and cell migration. Depletion of eosinophils with an anti-Siglec-F antibody provoked more severe clinical signs and increased liver damage than control animals which were accompanied by an increase in the production of IL-10 by hepatic and splenic CD4⁺ T cells. In addition, we also report that eosinophils participate in the modulation of humoral immune responses during F. hepatica infection, contributing to their degranulation. In conclusion, we demonstrate that eosinophils are beneficial for the host during F. hepatica infection, by limiting the production of IL-10 by specific CD4⁺ T cells and favoring eosinophil degranulation induced by specific antibodies. This work contributes to a better understanding of the role of eosinophils in parasitic helminth infections.

Fasciola hepatica-Derived Molecules as Regulators of the Host Immune Response

Helminths (worms) are one of the most successful organisms in nature given their ability to infect millions of humans and animals worldwide. Their success can be attributed to their ability to modulate the host immune response for their own benefit by releasing excretory-secretory (ES) products. Accordingly, ES products have been lauded as a potential source of immunomodulators/biotherapeutics for an array of inflammatory diseases. However, there is a significant lack of knowledge regarding the specific interactions between these products and cells of the immune response. Many different compounds have been identified within the helminth "secretome," including antioxidants, proteases, mucin-like peptides, as well as helminth defense molecules (HDMs), each with unique influences on the host inflammatory response. HDMs are a conserved group of proteins initially discovered in the secretome of the liver fluke, Fasciola hepatica. HDMs interact with cell membranes without cytotoxic effects and do not exert antimicrobial activity, suggesting that these peptides evolved specifically for immunomodulatory purposes. A peptide generated from the HDM sequence, termed FhHDM-1, has shown extensive anti-inflammatory abilities in clinically relevant models of diseases such as diabetes, multiple sclerosis, asthma, and acute lung injury, offering hope for the development of a new class of therapeutics. In this review, the current knowledge of host immunomodulation by a range of F. hepatica ES products, particularly FhHDM-1, will be discussed. Immune regulators, including HDMs, have been identified from other helminths and will also be outlined to broaden our understanding of the variety of effects these potent molecules exert on immune cells.

Eosinophil-Mediated Immune Control of Adult Filarial Nematode Infection Can Proceed in the Absence of IL-4 Receptor Signaling

Immunity to chronic filarial worm infection is apparent in IL-4Rα–deficient mice.

Delayed immunity in IL-4Rα^−/− mice is due to suboptimal tissue eosinophilia.

Eosinophil recruitment in the absence of IL-4R signaling requires CCR3 and IL-5.

Helminth infections are accompanied by eosinophilia in parasitized tissues. Eosinophils are effectors of immunity to tissue helminths. We previously reported that in the context of experimental filarial nematode infection, optimum tissue eosinophil recruitment was coordinated by local macrophage populations following IL-4R–dependent in situ proliferation and alternative activation. However, in the current study, we identify that control of chronic adult filarial worm infection is evident in IL-4Rα–deficient (IL-4Rα^−/−) mice, whereby the majority of infections do not achieve patency. An associated residual eosinophilia was apparent in infected IL-4Rα^−/− mice. By treating IL-4Rα^−/− mice serially with anti-CCR3 Ab or introducing a compound deficiency in CCR3 within IL-4Rα^−/− mice, residual eosinophilia was ablated, and susceptibility to chronic adult Brugia malayi infection was established, promoting a functional role for CCR3-dependent eosinophil influx in immune control in the absence of IL-4/IL-13–dependent immune mechanisms. We investigated additional cytokine signals involved in residual eosinophilia in the absence IL-4Rα signaling and defined that IL-4Rα^−/−/IL-5^−/− double-knockout mice displayed significant eosinophil deficiency compared with IL-4Rα^−/− mice and were susceptible to chronic fecund adult filarial infections. Contrastingly, there was no evidence that either IL-4R–dependent or IL-4R–independent/CCR3/IL-5–dependent immunity influenced B. malayi microfilarial loads in the blood. Our data demonstrate multiplicity of Th2-cytokine control of eosinophil tissue recruitment during chronic filarial infection and that IL-4R–independent/IL-5– and CCR3-dependent pathways are sufficient to control filarial adult infection via an eosinophil-dependent effector response prior to patency.

Deciphering the role of eosinophils in solid organ transplantation

Eosinophils are rare granulocytes that belong to the innate arm of the immune system. This cell population is traditionally defined as a destructive and cytotoxic mediator in asthma and helminth infection. Limited data in transplantation have suggested that eosinophils play a similar role in potentiating deleterious organ inflammation and immunologic rejection. Contrary to this long-held notion, recent data have uncovered the possibility that eosinophils play an alternative role in immune homeostasis, defense against a wide range of pathogens, as well as downregulation of deleterious inflammation. Specifically, translational data from small animal models of lung transplantation have demonstrated a critical role for eosinophils in the downregulation of alloimmunity. These findings shed new light on the unique immunologic features of the lung allograft and demonstrate that environmental polarization may alter the phenotype and function of leukocyte populations previously thought to be static in nature. In this review, we provide an update on eosinophils in the homeostasis of the lung as well as other solid organs.

Atypical Clinical Manifestations of Loiasis and Their Relevance for Endemic Populations

Background

Loiasis is mostly considered a relatively benign infection when compared with other filarial and parasitic diseases, with Calabar swellings and eyeworm being the most common signs. Yet, there are numerous reports in the literature of more serious sequelae. Establishing the relationship between infection and disease is a crucial first step toward estimating the burden of loiasis.

Methods

We conducted a systematic review of case reports containing 329 individuals and detailing clinical manifestations of loiasis with a focus on nonclassical, atypical presentations.

Results

Results indicate a high proportion (47%) of atypical presentations in the case reports identified, encompassing a wide range of cardiac, respiratory, gastrointestinal, renal, neurological, ophthalmological, and dermatological pathologies. Individuals with high microfilarial densities and residing in an endemic country were at greater risk of suffering from atypical manifestations.

Conclusions

Our findings have important implications for understanding the clinical spectrum of conditions associated with Loa loa infection, which extends well beyond the classical eyeworm and Calabar swellings. As case reports may overestimate the true rate of atypical manifestations in endemic populations, large-scale, longitudinal clinico-epidemiological studies will be required to refine our estimates and demonstrate causality between loiasis and the breadth of clinical manifestations reported. Even if the rates of atypical presentations were found to be lower, given that residents of loiasis-endemic areas are both numerous and the group most at risk of severe atypical manifestations, our conclusions support the recognition of loiasis as a significant public health burden across Central Africa.

Next-generation sequencing specifies Angiostrongylus eosinophilic meningoencephalitis in infants: Two case reports

RATIONALE

Angiostrongylus cantonensis-induced eosinophilic meningoencephalitis (AEM) in infants is a very rare but fatal disease. Utilization of genetic assay to detect the cerebral parasite plays an important role for the treatment of the infection.

PATIENT CONCERNS

Two infants (<2 years) presented with cough, intermittent fever, mental fatigue, and poor diet.

DIAGNOSIS

The patients were under clinical examination and laboratory test including cardiac ultrasound, chest X-ray, blood or cerebrospinal fluid (CSF) cell counting, serum enzyme-linked immunosorbent assay (ELISA), head magnetic resonance imaging (MRI) and next-generation sequencing (NGS) on DNA from CSF. Due to hypereosinophils in patients' peripheral blood and CSF, and abundant DNA sequences from A cantonensis in CSF, the patients were diagnosed with Angiostrongylus eosinophilic meningoencephalitis.

INTERVENTIONS

The patients were treated with albendazole to deworm, and methylprednisolone to reduce inflammation.

OUTCOME

The patients were completely recovered from AEM without relapse after 10-day treatment.

LESSONS

ELISA and MRI are not sufficiently accurate for the diagnosis of AEM in infants. NGS can specify the infection by the cerebral parasite and offers a new effective approach for the early and precise diagnosis of AEM in infants.

IL-4 receptor dependent expansion of lung CD169+ macrophages in microfilaria-driven inflammation

Lung disease is regularly reported in human filarial infections but the molecular pathogenesis of pulmonary filariasis is poorly understood. We used Litomosoides sigmodontis, a rodent filaria residing in the pleural cavity responsible for pleural inflammation, to model responses to human filarial infections and probe the mechanisms. Wild-type and Th2-deficient mice (ΔdblGata1 and Il-4receptor(r)a-/-/IL-5-/-) were infected with L. sigmodontis. Survival and growth of adult filariae and prevalence and density of microfilariae were evaluated. Cells and cytokines in the pleural cavity and bronchoalveolar space were characterized by imaging, flow cytometry and ELISA. Inflammatory pathways were evaluated by transcriptomic microarrays and lungs were isolated and analyzed for histopathological signatures. 40% of WT mice were amicrofilaremic whereas almost all mutant mice display blood microfilaremia. Microfilariae induced pleural, bronchoalveolar and lung-tissue inflammation associated with an increase in bronchoalveolar eosinophils and perivascular macrophages, production of mucus, visceral pleura alterations and fibrosis. Inflammation and pathology were decreased in Th2-deficient mice. An IL-4R-dependent increase of CD169 was observed on pleural and bronchoalveolar macrophages in microfilaremic mice. CD169+ tissue-resident macrophages were identified in the lungs with specific localizations. Strikingly, CD169+ macrophages increased significantly in the perivascular area in microfilaremic mice. These data describe lung inflammation and pathology in chronic filariasis and emphasize the role of Th2 responses according to the presence of microfilariae. It is also the first report implicating CD169+ lung macrophages in response to a Nematode infection.

Susceptibility to L. sigmodontis infection is highest in animals lacking IL-4R/IL-5 compared to single knockouts of IL-4R, IL-5 or eosinophils

Background

Mice are susceptible to infections with the rodent filarial nematode Litomosoides sigmodontis and develop immune responses that resemble those of human filarial infections. Thus, the L. sigmodontis model is used to study filarial immunomodulation, protective immune responses against filariae and to screen drug candidates for human filarial diseases. While previous studies showed that type 2 immune responses are protective against L. sigmodontis, the present study directly compared the impact of eosinophils, IL-5, and the IL-4R on the outcome of L. sigmodontis infection.

Methods

Susceptible wildtype (WT) BALB/c mice, BALB/c mice lacking eosinophils (dblGATA mice), IL-5^−/− mice, IL-4R^−/− mice and IL-4R^−/−/IL-5^−/− mice were infected with L. sigmodontis. Analyses were performed during the peak of microfilaremia in WT animals (71 dpi) as well as after IL-4R^−/−/IL-5^−/− mice showed a decline in microfilaremia (119 dpi) and included adult worm counts, peripheral blood microfilariae levels, cytokine production from thoracic cavity lavage, the site of adult worm residence, and quantification of major immune cell types within the thoracic cavity and spleen.

Results

Our study reveals that thoracic cavity eosinophil numbers correlated negatively with the adult worm burden, whereas correlations of alternatively activated macrophage (AAM) numbers with the adult worm burden (positive correlation) were likely attributed to the accompanied changes in eosinophil numbers. IL-4R^−/−/IL-5^−/− mice exhibited an enhanced embryogenesis achieving the highest microfilaremia with all animals becoming microfilariae positive and had an increased adult worm burden combined with a prolonged adult worm survival.

Conclusions

These data indicate that mice deficient for IL-4R^−/−/IL-5^−/− have the highest susceptibility for L. sigmodontis infection, which resulted in an earlier onset of microfilaremia, development of microfilaremia in all animals with highest microfilariae loads, and an extended adult worm survival.

Electronic supplementary material

The online version of this article (10.1186/s13071-019-3502-z) contains supplementary material, which is available to authorized users.

Host responses to intestinal nematodes

Helminth infection remains common in developing countries, where residents who suffer from the consequences of such infections can develop serious physical and mental disorders and often persist in the face of serious economic problems. Intestinal nematode infection induces the development of Th2-type immune responses including the B-cell IgE response; additionally, this infection induces an increase in the numbers and activation of various types of effector cells, such as mast cells, eosinophils and basophils, as well as the induction of goblet cell hyperplasia, anti-microbial peptide production and smooth-muscle contraction, all of which contribute to expel nematodes. Innate immunity is important in efforts to eliminate helminth infection; cytokines, including IL-25, IL-33 and thymic stromal lymphopoietin, which are products of epithelial cells and mast cells, induce Th2 cells and group 2 innate lymphoid cells to proliferate and produce Th2 cytokines. Nematodes also facilitate chronic infection by suppression of immune reactions through an increased number of Treg cells. Immunosuppression by parasite infection may ultimately be beneficial for the host animals; indeed, a negative correlation has been found between parasite infection and the prevalence of inflammatory disease in humans.

Human eosinophils and mast cells: Birds of a feather flock together

While the origin of the phrase "birds of a feather flock together" is unclear, it has been in use for centuries and is typically employed to describe the phenomenon that people with similar tastes or interests tend to seek each other out and congregate together. In this review, we have co-opted this phrase to compare innate immune cells of related origin, the eosinophil and mast cell, because they very often accumulate together in tissue sites under both homeostatic and inflammatory conditions. To highlight overlapping yet distinct features, their hematopoietic development, cell surface phenotype, mediator release profiles and roles in diseases have been compared and contrasted. What emerges is a sense that these two cell types often interact with each other and their tissue environment to provide synergistic contributions to a variety of normal and pathologic immune responses.

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.

Interleukin-4 activated macrophages mediate immunity to filarial helminth infection by sustaining CCR3-dependent eosinophilia

Eosinophils are effectors in immunity to tissue helminths but also induce allergic immunopathology. Mechanisms of eosinophilia in non-mucosal tissues during infection remain unresolved. Here we identify a pivotal function of tissue macrophages (Mϕ) in eosinophil anti-helminth immunity using a BALB/c mouse intra-peritoneal Brugia malayi filarial infection model. Eosinophilia, via C-C motif chemokine receptor (CCR)3, was necessary for immunity as CCR3 and eosinophil impairments rendered mice susceptible to chronic filarial infection. Post-infection, peritoneal Mϕ populations proliferated and became alternatively-activated (AAMϕ). Filarial AAMϕ development required adaptive immunity and interleukin-4 receptor-alpha. Depletion of Mϕ prior to infection suppressed eosinophilia and facilitated worm survival. Add back of filarial AAMϕ in Mϕ-depleted mice recapitulated a vigorous eosinophilia. Transfer of filarial AAMϕ into Severe-Combined Immune Deficient mice mediated immunological resistance in an eosinophil-dependent manner. Exogenous IL-4 delivery recapitulated tissue AAMϕ expansions, sustained eosinophilia and mediated immunological resistance in Mϕ-intact SCID mice. Co-culturing Brugia with filarial AAMϕ and/or filarial-recruited eosinophils confirmed eosinophils as the larvicidal cell type. Our data demonstrates that IL-4/IL-4Rα activated AAMϕ orchestrate eosinophil immunity to filarial tissue helminth infection.

Helminths parasitize approximately one quarter of the global population. Medically-important helminths, including filariae responsible for elephantiasis and river blindness, are targeted for elimination as a public health problem. Currently there are no vaccines or immunotherapeutics available for filarial worms or other human helminth pathogens. Here we define a cellular mechanism whereby the interlukin-4 dependent activation of tissue macrophages are essential to sustain the recruitment of larvicidal eosinophil granulocytes, leading to immunity against filarial infection at a sterile tissue site of parasitism. This work delineates the relative non-redundant functional roles of both myeloid cell types in ‘type-2’ immunity to helminth infection. The study represents a mechanistic advance in our understanding of how immunity operates against metazoan macroparasites invading sterile tissues and may be used in the rational design of new therapeutics to limit helminth disease.

Eosinophils from Physiology to Disease: A Comprehensive Review

Despite being the second least represented granulocyte subpopulation in the circulating blood, eosinophils are receiving a growing interest from the scientific community, due to their complex pathophysiological role in a broad range of local and systemic inflammatory diseases as well as in cancer and thrombosis. Eosinophils are crucial for the control of parasitic infections, but increasing evidence suggests that they are also involved in vital defensive tasks against bacterial and viral pathogens including HIV. On the other side of the coin, eosinophil potential to provide a strong defensive response against invading microbes through the release of a large array of compounds can prove toxic to the host tissues and dysregulate haemostasis. Increasing knowledge of eosinophil biological behaviour is leading to major changes in established paradigms for the classification and diagnosis of several allergic and autoimmune diseases and has paved the way to a "golden age" of eosinophil-targeted agents. In this review, we provide a comprehensive update on the pathophysiological role of eosinophils in host defence, inflammation, and cancer and discuss potential clinical implications in light of recent therapeutic advances.

Helminth Modulation of Lung Inflammation

Parasitic helminths must establish chronic infections to complete their life cycle and therefore are potent modulators of multiple facets of host physiology. Parasitic helminths have coevolved with humans to become arguably master selectors of our immune system, whereby they have impacted on the selection of genes with beneficial mutations for both host and parasite. While helminth infections of humans are a significant health burden, studies have shown that helminths or helminth products can alter susceptibility to unrelated infectious or inflammatory diseases. This has generated interest in the use of helminth infections or molecules as therapeutics. In this review, we focus on the impact of helminth infections on pulmonary immunity, especially with regard to homeostatic lung function, pulmonary viral and bacterial (co)infections, and asthma.

MicroRNA-mediated regulation of immune responses to intestinal helminth infections

Intestinal helminth infections are highly prevalent in the developing world, often resulting in chronic infection and inflicting high host morbidity. With the emergence of drug-resistant parasites, a limited number of chemotherapeutic drugs available and stalling vaccine efforts, an increased understanding of antihelminth immunity is essential to provide new avenues to therapeutic intervention. MicroRNAs are a class of small, nonprotein coding RNAs which negatively regulate mRNA translation, thus providing finite control over gene expression in a plethora of biological settings. The miRNA-mediated coordinated control of gene expression has been shown to be essential in infection and immunity, in promoting and fine-tuning the appropriate immune response. This review gathers together and discusses observations of miRNA-mediated effects on the immune system and the subsequent impact on our understanding of antihelminth immunity.

In vivo neutralization of α4 and β7 integrins inhibits eosinophil trafficking and prevents lung injury during tropical pulmonary eosinophilia in mice

Integrins regulate leukocyte trafficking during homeostasis and inflammatory conditions. However, the role of α4 and β7 integrins in guiding eosinophil transmigration into the lungs during filarial manifestation of Tropical Pulmonary Eosinophilia (TPE) has not been explored. In this study, mice exhibiting TPE manifestations were administered with in vivo neutralizing antibodies against integrins α4 and β7 or their combination and immuno-pathological parameters were evaluated. Results show an intact lung barrier, significantly lower lung inflammation and reduced eosinophil counts in the Bronchoalveolar lavage fluid and lungs of mice receiving anti-α4⁺ β7 treatment. Reduced eosinophil peroxidase and β-hexosaminidase activity, downregulation of inflammatory genes, lower production of inflammatory lipid intermediates like prostaglandins E2 and D2, leukotriene B4 and cysteinyl leukotrienes were also noted in anti-α4⁺ β7 treated mice. Reduced accumulation of central memory, effector memory, regulatory T cells and lower production of IL-4, IL-5, and TGF-β were other cardinal features of anti-α4⁺ β7 treated mice lungs. Flow cytometry-sorted lung eosinophils from anti-α4⁺ β7 treated mice showed higher apoptotic potential, downregulated anti-apoptotic gene Bcl-2, and exhibited reduced F-actin polymerization and calcium influx as compared to IgG controls. In summary, neutralization of α4⁺ β7 integrins impairs the transmigration, activation and survival of eosinophils and reduces TPE induced pathology in mice lungs.

Immune responses induced by co-infection with Capillaria hepatica in Clonorchis sinensis-infected rats

Clonorchis sinensis and Capillaria hepatica are zoonotic parasites that mainly infect the liver and cause serious liver disorders. However, immunological parameters induced by co-infection with these parasites remain unknown. In this study, for the first time, we investigated immunological profiles induced by co-infection with C. hepatica (CH) in C. sinensis (CS)-infected rats (Sprague-Dawley). Rats were infected primarily with 50 metacercariae of C. sinensis; 4 weeks later, they were subsequently infected with 1000 infective C. hepatica eggs. Significantly higher levels of C. sinensis- or C. hepatica-specific IgG antibodies were found in the sera of rats. Interestingly, no cross-reacting antibody was observed between C. sinensis and C. hepatica infections. Significantly raised eosinophil levels were found in the blood of C. sinensis/C. hepatica co-infected rats (CS + CH) compared to the blood of rats infected singly with C. sinensis. Co-infected rats showed significantly higher levels of lymphocyte proliferation and cytokine production compared to a single C. sinensis infection. The worm burden of C. sinensis was significantly reduced in co-infected rats compared to the single C. sinensis infection. These results indicate that the eosinophils, lymphocyte proliferation and cytokine production induced by subsequent infection with C. hepatica in C. sinensis-infected rats might contribute to the observed C. sinensis worm reduction.

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.

Pathological manifestations in lymphatic filariasis correlate with lack of inhibitory properties of IgG4 antibodies on IgE-activated granulocytes

Helminth parasites are known to be efficient modulators of their host's immune system. To guarantee their own survival, they induce alongside the classical Th2 a strong regulatory response with high levels of anti-inflammatory cytokines and elevated plasma levels of IgG4. This particular antibody was shown in different models to exhibit immunosuppressive properties. How IgG4 affects the etiopathology of lymphatic filariasis (LF) is however not well characterized. Here we investigate the impact of plasma and affinity-purified IgG/IgG4 fractions from endemic normals (EN) and LF infected pathology patients (CP), asymptomatic microfilaraemic (Mf+) and amicrofilaraemic (Mf-) individuals on IgE/IL3 activated granulocytes. The activation and degranulation states were investigated by monitoring the expression of CD63/HLADR and the release of granule contents (neutrophil elastase (NE), eosinophil cationic protein (ECP) and histamine) respectively by flow cytometry and ELISA. We could show that the activation of granulocytes was inhibited in the presence of plasma from EN and Mf+ individuals whereas those of Mf- and CP presented no effect. This inhibitory capacity was impaired upon depletion of IgG in Mf+ individuals but persisted in IgG-depleted plasma from EN, where it strongly correlated with the expression of IgA. In addition, IgA-depleted fractions failed to suppress granulocyte activation. Strikingly, affinity-purified IgG4 antibodies from EN, Mf+ and Mf- individuals bound granulocytes and inhibited activation and the release of ECP, NE and histamine. In contrast, IgG4 from CP could not bind granulocytes and presented no suppressive capacity. Reduction of both the affinity to, and the suppressive properties of anti-inflammatory IgG4 on granulocytes was reached only when FcγRI and II were blocked simultaneously. These data indicate that IgG4 antibodies from Mf+, Mf- and EN, in contrast to those of CP, natively exhibit FcγRI/II-dependent suppressive properties on granulocytes. Our findings suggest that quantitative and qualitative alterations in IgG4 molecules are associated with the different clinical phenotypes in LF endemic regions.

Immune signatures of pathogenesis in the peritoneal compartment during early infection of sheep with Fasciola hepatica

Immune signatures of sheep acutely-infected with Fasciola hepatica, an important pathogen of livestock and humans were analysed within the peritoneal compartment to investigate early infection. Within the peritoneum, F. hepatica antibodies coincided with an intense innate and adaptive cellular immune response, with infiltrating leukocytes and a marked eosinophilia (49%). However, while cytokine qPCR analysis revealed IL-10, IL-12, IL-13, IL-23 and TGFβ were elevated, these were not statistically different at 18 days post-infection compared to uninfected animals indicating that the immune response is muted and not yet skewed to a Th2 type response that is associated with chronic disease. Proteomic analysis of the peritoneal fluid identified infection-related proteins, including several structural proteins derived from the liver extracellular matrix, connective tissue and epithelium, and proteins related to the immune system. Periostin and vascular cell adhesion protein 1 (VCAM-1), molecules that mediate leukocyte infiltration and are associated with inflammatory disorders involving marked eosinophilia (e.g. asthma), were particularly elevated in the peritoneum. Immuno-histochemical studies indicated that the source of periostin and VCAM-1 was the inflamed sheep liver tissue. This study has revealed previously unknown aspects of the immunology and pathogenesis associated with acute fascioliasis in the peritoneum and liver.

Dopaminergic Regulation of Innate Immunity: a Review

Dopamine (DA) is a neurotransmitter in the central nervous system as well as in peripheral tissues. Emerging evidence however points to DA also as a key transmitter between the nervous system and the immune system as well as a mediator produced and released by immune cells themselves. Dopaminergic pathways have received so far extensive attention in the adaptive branch of the immune system, where they play a role in health and disease such as multiple sclerosis, rheumatoid arthritis, cancer, and Parkinson's disease. Comparatively little is known about DA and the innate immune response, although DA may affect innate immune system cells such as dendritic cells, macrophages, microglia, and neutrophils. The present review aims at providing a complete and exhaustive summary of currently available evidence about DA and innate immunity, and to become a reference for anyone potentially interested in the fields of immunology, neurosciences and pharmacology. A wide array of dopaminergic drugs is used in therapeutics for non-immune indications, such as Parkinson's disease, hyperprolactinemia, shock, hypertension, with a usually favorable therapeutic index, and they might be relatively easily repurposed for immune-mediated disease, thus leading to innovative treatments at low price, with benefit for patients as well as for the healthcare systems.

Brugia malayi microfilariae adhere to human vascular endothelial cells in a C3-dependent manner

Brugia malayi causes the human tropical disease, lymphatic filariasis. Microfilariae (Mf) of this nematode live in the bloodstream and are ingested by a feeding mosquito vector. Interestingly, in a remarkable co-evolutionary adaptation, Mf appearance in the peripheral blood follows a circadian periodicity and reaches a peak when the mosquito is most likely to feed. For the remaining hours, the majority of Mf sequester in the lung capillaries. This circadian phenomenon has been widely reported and is likely to maximise parasite fitness and optimise transmission potential. However, the mechanism of Mf sequestration in the lungs remains largely unresolved. In this study, we demonstrate that B. malayi Mf can, directly adhere to vascular endothelial cells under static conditions and under flow conditions, they can bind at high (but not low) flow rates. High flow rates are more likely to be experienced diurnally. Furthermore, a non-periodic nematode adheres less efficiently to endothelial cells. Strikingly C3, the central component of complement, plays a crucial role in the adherence interaction. These novel results show that microfilariae have the ability to bind to endothelial cells, which may explain their sequestration in the lungs, and this binding is increased in the presence of inflammatory mediators.

Eosinophils in Helminth Infection: Defenders and Dupes

Eosinophilia is a central feature of the host response to helminth infection. Larval stages of parasitic worms are killed in vitro by eosinophils in the presence of specific antibodies or complement. These findings established host defense as the paradigm for eosinophil function. Recently, studies in eosinophil-ablated mouse strains have revealed an expanded repertoire of immunoregulatory functions for this cell. Other reports document crucial roles for eosinophils in tissue homeostasis and metabolism, processes that are central to the establishment and maintenance of parasitic worms in their hosts. In this review, we summarize current understanding of the significance of eosinophils at the host-parasite interface, highlighting their distinct functions during primary and secondary exposure.

CD4 T-cell hyporesponsiveness induced by schistosome larvae is not dependent upon eosinophils but may involve connective tissue mast cells

In areas endemic for schistosomiasis, people can often be in contact with contaminated water resulting in repeated exposures to infective Schistosoma mansoni cercariae. Using a murine model, repeated infections result in IL‐10‐dependent CD4⁺ T‐cell hyporesponsiveness in the skin‐draining lymph nodes (sdLN), which could be caused by an abundance of eosinophils and connective tissue mast cells at the skin infection site. Here, we show that whilst the absence of eosinophils did not have a significant effect on cytokine production, MHC‐II⁺ cells were more numerous in the dermal cell exudate population. Nevertheless, the absence of dermal eosinophils did not lead to an increase in the responsiveness of CD4⁺ T cells in the sdLN, revealing that eosinophils in repeatedly exposed skin did not impact on the development of CD4⁺ T‐cell hyporesponsiveness. On the other hand, the absence of connective tissue mast cells led to a reduction in dermal IL‐10 and to an increase in the number of MHC‐II⁺ cells infiltrating the skin. There was also a small but significant alleviation of hyporesponsiveness in the sdLN, suggesting that mast cells may have a role in regulating immune responses after repeated exposures of the skin to S. mansoni cercariae.

Reduced Leukocyte Infiltration in Absence of Eosinophils Correlates with Decreased Tissue Damage and Disease Susceptibility in ΔdblGATA Mice during Murine Neurocysticercosis

Neurocysticercosis (NCC) is one of the most common helminth parasitic diseases of the central nervous system (CNS) and the leading cause of acquired epilepsy worldwide. NCC is caused by the presence of the metacestode larvae of the tapeworm Taenia solium within brain tissues. NCC patients exhibit a long asymptomatic phase followed by a phase of symptoms including increased intra-cranial pressure and seizures. While the asymptomatic phase is attributed to the immunosuppressive capabilities of viable T. solium parasites, release of antigens by dying organisms induce strong immune responses and associated symptoms. Previous studies in T. solium-infected pigs have shown that the inflammatory response consists of various leukocyte populations including eosinophils, macrophages, and T cells among others. Because the role of eosinophils within the brain has not been investigated during NCC, we examined parasite burden, disease susceptibility and the composition of the inflammatory reaction in the brains of infected wild type (WT) and eosinophil-deficient mice (ΔdblGATA) using a murine model of NCC in which mice were infected intracranially with Mesocestoides corti, a cestode parasite related to T. solium. In WT mice, we observed a time-dependent induction of eosinophil recruitment in infected mice, contrasting with an overall reduced leukocyte infiltration in ΔdblGATA brains. Although, ΔdblGATA mice exhibited an increased parasite burden, reduced tissue damage and less disease susceptibility was observed when compared to infected WT mice. Cellular infiltrates in infected ΔdblGATA mice were comprised of more mast cells, and αβ T cells, which correlated with an abundant CD8⁺ T cell response and reduced CD4⁺ Th1 and Th2 responses. Thus, our data suggest that enhanced inflammatory response in WT mice appears detrimental and associates with increased disease susceptibility, despite the reduced parasite burden in the CNS. Overall reduced leukocyte infiltration due to absence of eosinophils correlates with attenuated tissue damage and longer survival of ΔdblGATA mice. Therefore, our study suggests that approaches to clear NCC will require strategies to tightly control the host immune response while eradicating the parasite with minimal damage to brain tissue.

Eosinophils are known to mediate a protective response against several parasitic infections. This is largely accomplished by eosinophil degranulation (direct killing) and modulating effective adaptive immune responses. Consequently, eosinophils can also contribute to host pathology via a bystander effect. However, the outcome of infection varies depending upon the parasite species. In the case of neurocysticercosis (NCC), the role of eosinophils in disease progression has not been investigated despite the known eosinophilic response in patients. NCC is one of the most common parasitic diseases of the brain which is caused by the metacestode (larva) of the tapeworm Taenia solium. To determine the role of eosinophils in NCC disease outcome, we used a murine model of NCC in which wildtype (WT) or eosinophil deficient mice (ΔdblGATA) were infected intracranially with Mesocestoides corti, a cestode parasite related to T. solium. Our data show that murine NCC is characterized by a robust eosinophil response that correlates with lower parasite burden in the brain. Comparison of T cell response reveals a mixed Th1/Th2 in the WT brain, and ΔdblGATA mice showed a significant decrease in both population but in particular in the Th2 response. In addition, the strong eosinophil reaction observed in WT brains correlates with exacerbated pathology and increased morbidity. Thus, our study suggest that eosinophils act as a double-edged sword playing a role in controlling the infection but worsening the disease outcome by contributing to host pathology.

The role of IL-33/ST2, IL-4, and eosinophils on the airway hyperresponsiveness induced by Strongyloides venezuelensis in BALB/c mice

Strongyloidiasis is a neglected chronic nematode infection, in which the control of autoinfection rate and severity of disease is dependent on type 2 immune responses. Strongyloides also causes Th2 responses in the lung of infected animals and changes in airway function, including airway hyperresponsiveness (AHR). Mechanisms of AHR during Strongyloides venezuelensis infection are not entirely known, and we investigate here the role of IL-4, eosinophils, and IL-33/ST2. AHR was evaluated in infected mice by determining changes in lung function after increasing doses of methacholine. Balb/C, but no C57Bl/6, mice developed AHR, tissue eosinophilia, and increased local IL-4 and IL-5 production. Functional changes peaked at day 4 and 7, after the larva had left the lungs. AHR was clearly dependent on IL-4 but not on eosinophils, as evaluated by experiments in IL-4 and Gata-1-deficient mice. Experiments in ST2-deficient mice showed that this pathway was not needed for induction of AHR but was necessary for the maintenance of AHR and for Th2 responses in the lung. These studies clearly show a crucial role for IL-4 in the induction of AHR following S. venezuelensis infection and for IL-33/ST2 in maintaining AHR and lung Th2 responses.

Cystatin F Ensures Eosinophil Survival by Regulating Granule Biogenesis

Eosinophils are now recognized as multifunctional leukocytes that provide critical homeostatic signals to maintain other immune cells and aid tissue repair. Paradoxically, eosinophils also express an armory of granule-localized toxins and hydrolases believed to contribute to pathology in inflammatory disease. How eosinophils deliver their supporting functions while avoiding self-inflicted injury is poorly understood. We have demonstrated that cystatin F (CF) is a critical survival factor for eosinophils. Eosinophils from CF null mice had reduced lifespan, reduced granularity, and disturbed granule morphology. In vitro, cysteine protease inhibitors restored granularity, demonstrating that control of cysteine protease activity by CF is critical for normal eosinophil development. CF null mice showed reduced pulmonary pathology in a model of allergic lung inflammation but also reduced ability to combat infection by the nematode Brugia malayi. These data identify CF as a "cytoprotectant" that promotes eosinophil survival and function by ensuring granule integrity. VIDEO ABSTRACT.

A Player and Coordinator: The Versatile Roles of Eosinophils in the Immune System

Eosinophils have traditionally been associated with allergic diseases and parasite infection. Research advances in the recent decades have brought evolutionary changes in our understanding of eosinophil biology and its roles in immunity. It is currently recognized that eosinophils play multiple roles in both innate and adaptive immunity. As effector cells in innate immunity, eosinophils exert a pro-inflammatory and destructive role in the Th2 immune response associated with allergic inflammation or parasite infection. Eosinophils can also be recruited by danger signals released by pathogen infections or tissue injury, inducing host defense against parasitic, fungal, bacterial or viral infection or promoting tissue repair and remodeling. Eosinophils also serve as nonprofessional antigen-presenting cells in response to allergen challenge or helminth infection, and, meanwhile, are known to function as a versatile coordinator that actively regulates or interacts with various immune cells including T lymphocytes and dendritic cells. More roles of eosinophils implicated in immunity have been proposed including in immune homeostasis, allograft rejection, and anti-tumor immunity. Eosinophil interactions with structural cells are also implicated in the mechanisms in allergic inflammation and in Helicobacter pylori gastritis. These multifaceted roles of eosinophils as both players and coordinators in immune system are discussed in this review.

The Identification of Haemonchus Species and Diagnosis of Haemonchosis

Diagnosis is often equated with identification or detection when discussing parasitic diseases. Unfortunately, these are not necessarily mutually exclusive activities; diseases and infections are generally diagnosed and organisms are identified. Diagnosis is commonly predicated upon some clinical signs; in an effort to determine the causative agent, identification of genera and species is subsequently performed. Both identification and diagnosis play critical roles in managing an infection, and involve the interplay of direct and indirect methods of detection, particularly in light of the complex and expanding problem of drug-resistance in parasites. Accurate and authoritative identification that is cost- and time-effective, based on structural and molecular attributes of specimens, provides a foundation for defining parasite diversity and changing patterns of geographical distribution, host association and emergence of disease. Most techniques developed thus far have been grounded in assumptions based on strict host associations between Haemonchus contortus and small ruminants, that is, sheep and goats, and between Haemonchus placei and bovids. Current research and increasing empirical evidence of natural infections in the field demonstrates that this assumption misrepresents the host associations for these species of Haemonchus. Furthermore, the capacity of H. contortus to utilize a considerably broad spectrum of ungulate hosts is reflected in our understanding of the role of anthropogenic forcing, the 'breakdown' of ecological isolation, global introduction and host switching as determinants of distribution. Nuanced insights about distribution, host association and epidemiology have emerged over the past 30years, coincidently with the development of increasingly robust means for parasite identification. In this review and for the sake of argument, we would like to delineate the diagnosis of haemonchosis from the identification of the specific pathogen. As a foundation for exploring host and parasite biology, we will examine the evolution of methods for distinguishing H. contortus from other common gastrointestinal nematodes of agriculturally significant and free-ranging wild ruminants using morphological, molecular and/or immunological methods for studies at the species and genus levels.

Fasciola hepatica induces eosinophil apoptosis in the migratory and biliary stages of infection in sheep

The aim of the present work was to evaluate the number of apoptotic eosinophils in the livers of sheep experimentally infected with Fasciola hepatica during the migratory and biliary stages of infection. Four groups (n=5) of sheep were used; groups 1-3 were orally infected with 200 metacercariae (mc) and sacrificed at 8 and 28 days post-infection (dpi), and 17 weeks post-infection (wpi), respectively. Group 4 was used as an uninfected control. Apoptosis was detected using immunohistochemistry with a polyclonal antibody against anti-active caspase-3, and transmission electron microscopy (TEM). Eosinophils were identified using the Hansel stain in serial sections for caspase-3, and by ultrastructural features using TEM. At 8 and 28 dpi, numerous caspase-3(+) eosinophils were mainly found at the periphery of acute hepatic necrotic foci. The percentage of caspase -3(+) apoptotic eosinophils in the periphery of necrotic foci was high (46.1-53.9) at 8 and 28 dpi, respectively, and decreased in granulomas found at 28 dpi (6%). Transmission electron microscopy confirmed the presence of apoptotic eosinophils in hepatic lesions at 8 and 28 dpi. At 17 wpi, apoptotic eosinophils were detected in the infiltrate surrounding some enlarged bile ducts containing adult flukes. This is the first report of apoptosis induced by F. hepatica in sheep and the first study reporting apoptosis in eosinophils in hepatic inflammatory infiltrates in vivo. The high number of apoptotic eosinophils in acute necrotic tracts during the migratory and biliary stages of infection suggests that eosinophil apoptosis may play a role in F. hepatica survival during different stages of infection.