Early stages of Ascaris suum induce airway inflammation and hyperreactivity in a mouse model

Host resources and parasite traits interact to determine the optimal combination of host parasite-mitigation strategies

Organisms have evolved diverse strategies to manage parasite infections. Broadly, hosts may avoid infection by altering behaviour, resist infection by targeting parasites or tolerate infection by repairing associated damage. The effectiveness of a strategy depends on interactions between, for example, resource availability, parasite traits (virulence, life-history) and the host itself (nutritional status, immunopathology). To understand how these factors shape host parasite-mitigation strategies, we developed a mathematical model of within-host, parasite-immune dynamics in the context of helminth infections. The model incorporated host nutrition and resource allocation to different mechanisms of immune response: larval parasite prevention; adult parasite clearance; damage repair (tolerance). We also considered a non-immune strategy: avoidance via anorexia, reducing intake of infective stages. Resources not allocated to immune processes promoted host condition, whereas harm due to parasites and immunopathology diminished it. Maximising condition (a proxy for fitness), we determined optimal host investment for each parasite-mitigation strategy, singly and combined, across different environmental resource levels and parasite trait values. Which strategy was optimal varied with scenario. Tolerance generally performed well, especially with high resources. Success of the different resistance strategies (larval prevention or adult clearance) tracked relative virulence of larval and adult parasites: slowly maturing, highly damaging larvae favoured prevention; rapidly maturing, less harmful larvae favoured clearance. Anorexia was viable only in the short term, due to reduced host nutrition. Combined strategies always outperformed any lone strategy: these were dominated by tolerance, with some investment in resistance. Choice of parasite mitigation strategy has profound consequences for hosts, impacting their condition, survival and reproductive success. We show that the efficacy of different strategies is highly dependent on timescale, parasite traits and resource availability. Models that integrate such factors can inform the collection and interpretation of empirical data, to understand how those drivers interact to shape host immune responses in natural systems.

The effects of exercise training on the lungs and cardiovascular function of animals exposed to diesel exhaust particles and gases

Air pollution has been identified as one of the main environmental risks to health. Since exercise training seems to act as an anti-inflammatory modulator, our hypothesis is that exercise training prevents damage to respiratory and cardiovascular function caused by diesel exhaust particle (DEP) exposure. This study aimed to evaluate whether aerobic exercise training prior to DEP exposure prevents inflammatory processes in the pulmonary and cardiovascular systems. Therefore, BALB/C male mice were or were not submitted to a 10-week exercise training protocol (5×/week, 1 h/d), and after four weeks, they were exposed to DEP in a chamber with 24 μg/m³ PM2.5 or filtered air. Heart rate variability, lung mechanics and bronchoalveolar lavage fluid, cytokines and polymorphonuclear cells in the lung parenchyma were evaluated. Exposure to DEPs reduced heart rate variability and the elastance of the respiratory system and increased the number of cells in bronchoalveolar lavage fluid, as well as macrophages, neutrophils and lymphocytes, the density of polymorphonuclear cells and the proportion of collagen fibres in the lung parenchyma. Additionally, DEP-exposed animals showed increased expression of IL-23 and IL-12p40 (proinflammatory cytokines) and inducible nitric oxide synthase. Exercise training avoided the increases in all these inflammatory parameters, except the elastance of the respiratory system, the amount of collagen fibres and the expression of inducible nitric oxide synthase. Additionally, trained animals showed increased expression of the anti-inflammatory cytokine IL-1ra. Although our data showed a reduction in proinflammatory markers and an increase in markers of the anti-inflammatory pathway, these changes were not sufficient to prevent damage to the lung and cardiovascular function induced by DEPs. Based on these data, we propose that aerobic exercise training prevents the lung inflammatory process induced by DEPs, although it was not sufficient to avoid chronic damage, such as a loss of lung function or cardiovascular events.

Concomitant experimental coinfection by Plasmodium berghei NK65-NY and Ascaris suum downregulates the Ascaris-specific immune response and potentiates Ascaris-associated lung pathology

Background

Ascariasis and malaria are highly prevalent parasitic diseases in tropical regions and often have overlapping endemic areas, contributing to high morbidity and mortality rates in areas with poor sanitary conditions. Several studies have previously aimed to correlate the effects of Ascaris-Plasmodium coinfections but have obtained contradictory and inconclusive results. Therefore, the present study aimed to investigate parasitological and immunopathological aspects of the lung during murine experimental concomitant coinfection by Plasmodium berghei and Ascaris suum during larvae ascariasis.

Methods

C57BL/6J mice were inoculated with 1 × 10⁴P. berghei strain NK65-NY-infected red blood cells (iRBCs) intraperitoneally and/or 2500 embryonated eggs of A. suum by oral gavage. P. berghei parasitaemia, morbidity and the survival rate were assessed. On the seventh day postinfection (dpi), A. suum lung burden analysis; bronchoalveolar lavage (BAL); histopathology; NAG, MPO and EPO activity measurements; haematological analysis; and respiratory mechanics analysis were performed. The concentrations of interleukin (IL)-1β, IL-12/IL-23p40, IL-6, IL-4, IL-33, IL-13, IL-5, IL-10, IL-17A, IFN-γ, TNF and TGF-β were assayed by sandwich ELISA.

Results

Animals coinfected with P. berghei and A. suum show decreased production of type 1, 2, and 17 and regulatory cytokines; low leukocyte recruitment in the tissue; increased cellularity in the circulation; and low levels of NAG, MPO and EPO activity that lead to an increase in larvae migration, as shown by the decrease in larvae recovered in the lung parenchyma and increase in larvae recovered in the airway. This situation leads to severe airway haemorrhage and, consequently, an impairment respiratory function that leads to high morbidity and early mortality.

Conclusions

This study demonstrates that the Ascaris-Plasmodium interaction is harmful to the host and suggests that this coinfection may potentiate Ascaris-associated pathology by dampening the Ascaris-specific immune response, resulting in the early death of affected animals.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12936-021-03824-w.

Distinct hepatic myeloid and lymphoid cell repertoires are associated with susceptibility and resistance to Ascaris infection

The soil-transmitted helminth Ascaris lumbricoides infects ~800 million people worldwide. Some people are heavily infected, harbouring many worms, whereas others are only lightly infected. The mechanisms behind this difference are unknown. We used a mouse model of hepatic resistance to Ascaris, with C57BL/6J mice as a model for heavy infection and CBA/Ca mice as a model for light infection. The mice were infected with the porcine ascarid, Ascaris suum or the human ascarid, A. lumbricoides and immune cells in their livers and spleens were enumerated using flow cytometry. Compared to uninfected C57BL/6J mice, uninfected CBA/Ca mice had higher splenic CD4+ and γδ T cell counts and lower hepatic eosinophil, Kupffer cell and B cell counts. Infection with A. suum led to expansions of eosinophils, Kupffer cells, monocytes and dendritic cells in the livers of both mouse strains and depletions of hepatic natural killer (NK) cells in CBA/Ca mice only. Infection with A. lumbricoides led to expansions of hepatic eosinophils, monocytes and dendritic cells and depletions of CD8+, αβ, NK and NK T cells in CBA/Ca mice, but not in C57BL/6J mice where only monocytes expanded. Thus, susceptibility and resistance to Ascaris infection are governed, in part, by the hepatic immune system.

The long and winding road of Ascaris larval migration: the role of mouse models

Ascaris lumbricoides and Ascaris suum are helminth parasites of humans and pigs, respectively. The life cycle of Ascaris sets it apart from the other soil-transmitted helminths because of its hepato-tracheal migration. Larval migration contributes to underestimated morbidity in humans and pigs. This migration, coupled with a lack of a murine model in which the Ascaris parasite might complete its life cycle, has undoubtedly contributed to the neglected status of the ascarid. Our knowledge of the epidemiology of adult worm infections had led us to an enhanced understanding of patterns of infection such as aggregation and predisposition; however, the mechanisms underlying these complex phenomena remain elusive. Carefully controlled experiments in defined inbred strains of mice – with enhanced recovery of larvae in tandem with measurements of cellular, histopathological and molecular processes – have greatly enhanced our knowledge of the early phase of infection, a phase crucial to the success or failure of adult worm establishment. Furthermore, the recent development of a mouse model of susceptibility and resistance, with highly consistent and diverging Ascaris larval burdens in the murine lungs, represents the extremes of the host phenotype displayed in the aggregated distribution of worms and provides an opportunity to explore the mechanistic basis that confers predisposition to light and heavy Ascaris infection. Certainly, detailed knowledge of the cellular hepatic and pulmonary responses at the molecular level can be accrued from murine models of infection and, once available, may enhance our ability to develop immunomodulatory therapies to elicit resistance to infection.

Helminth-derived cystatins: the immunomodulatory properties of an Ascaris lumbricoides cystatin

Helminth infections such as ascariasis elicit a type 2 immune response resembling that involved in allergic inflammation, but differing to allergy, they are also accompanied with strong immunomodulation. This has stimulated an increasing number of investigations, not only to better understand the mechanisms of allergy and helminth immunity but to find parasite-derived anti-inflammatory products that could improve the current treatments of chronic non-communicable inflammatory diseases such as asthma. A great number of helminth-derived immunomodulators have been discovered and some of them extensively analysed, showing their potential use as anti-inflammatory drugs in clinical settings. Since Ascaris lumbricoides is one of the most successful parasites, several groups have focused on the immunomodulatory properties of this helminth. As a result, several excretory/secretory components and purified molecules have been analysed, revealing interesting anti-inflammatory activities potentially useful as therapeutic tools. One of these molecules is A. lumbricoides cystatin, whose genomic, cellular, molecular, and immunomodulatory properties are described in this review.

Evaluation of the effect of Toxocara cati infection in the mouse model of allergic asthma: Exacerbation of allergic asthma symptoms and Th2 types of response

Toxocariasis is considered a neglected disease despite the importance of Toxocara spp. infections for human health and is little recognized as a significant problem by public health institutions in developing countries. Epidemiological studies suggest that infection with Toxocara cati contributes to the development of allergic asthma.In the present study, we investigated the effect of T. cati infection on experimental allergic airway inflammation using murine model. BALB/c mice were infected by oral administration with 500 embryonated T. cati eggs followed by ovalbumin (OVA) sensitization and challenge to induce allergic airway inflammation. Infection with T. cati in combination with OVA treatment leads to exacerbation of pulmonary inflammation, eosinophilia, airway hyperresponsiveness, OVA specific IgE. Cytokines measurement in bronchoalveolar lavage indicated that the levels of IL-4 and IL-5 in BAL fluid significantly increased after T. cati infected, OVA treated or a combination of both. Increased level of IL-5 was measured in the lungs of T. cati-infected or OVA-treated mice compared with controls. Moreover, combining infection and OVA treatment significantly increase the level of these cytokines. A direct association between T. cati infection and asthma was found in murine model. Although a wide range of helminth species have been demonstrated to modulate allergic responses, most notably the intestinal nematode T. cati, increases airway hyperresponsiveness, lung histopathology, eosinophil recruitment, and Th2 cytokines in alum-sensitized models of airway allergy.

Allergen presensitization drives an eosinophil-dependent arrest in lung-specific helminth development

This study investigates the relationship between helminth infection and allergic sensitization by assessing the influence of preexisting allergy on the outcome of helminth infections, rather than the more traditional approach in which the helminth infection precedes the onset of allergy. Here we used a murine model of house dust mite-induced (HDM-induced) allergic inflammation followed by Ascaris infection to demonstrate that allergic sensitization drives an eosinophil-rich pulmonary type 2 immune response (Th2 cells, M2 macrophages, type 2 innate lymphoid cells, IL-33, IL-4, IL-13, and mucus) that directly hinders larval development and reduces markedly the parasite burden in the lungs. This effect is dependent on the presence of eosinophils, as eosinophil-deficient mice were unable to limit parasite development or numbers. In vivo administration of neutralizing antibodies against CD4 prior to HDM sensitization significantly reduced eosinophils in the lungs, resulting in the reversal of the HDM-induced Ascaris larval killing. Our data suggest that HDM allergic sensitization drives a response that mimics a primary Ascaris infection, such that CD4+ Th2-mediated eosinophil-dependent helminth larval killing in the lung tissue occurs. This study provides insight into the mechanisms underlying tissue-specific responses that drive a protective response against the early stages of the helminths prior to their establishing long-lasting infections in the host.

Ascariasis as a model to study the helminth/allergy relationships

Ascariasis is the most frequent soil transmitted helminthiasis and, as well as other helminth infections, is expected to influence the clinical presentation of allergic diseases such as asthma. Indeed, several clinical and experimental works have shown an important impact either increasing or suppressing symptoms, and the same effects have been detected on the underlying immune responses. In this review we analyze the work on this field performed in Colombia, a Latin American tropical country, including aspects such as the molecular genetics of the IgE response to Ascaris; the allergenic activity of Ascaris IgE-binding molecular components and the immunological and clinical influences of ascariasis on asthma. The analysis allows us to conclude that the impact of ascariasis on the inception and evolution of allergic diseases such as asthma deserves more investigation, but advances have been made during the last years. The concurrent parasite-induced immunostimulatory and immunosuppressive effects during this helminthiasis do modify the natural history of asthma and some aspects of the practice of allergology in the tropics. Theoretically it can also influence the epidemiological trends of allergic diseases either by its absence or presence in different regions and countries.

A comprehensive analysis of the faecal microbiome and metabolome of Strongyloides stercoralis infected volunteers from a non-endemic area

Data from recent studies support the hypothesis that infections by human gastrointestinal (GI) helminths impact, directly and/or indirectly, on the composition of the host gut microbial flora. However, to the best of our knowledge, these studies have been conducted in helminth-endemic areas with multi-helminth infections and/or in volunteers with underlying gut disorders. Therefore, in this study, we explore the impact of natural mono-infections by the human parasite Strongyloides stercoralis on the faecal microbiota and metabolic profiles of a cohort of human volunteers from a non-endemic area of northern Italy (S+), pre- and post-anthelmintic treatment, and compare the findings with data obtained from a cohort of uninfected controls from the same geographical area (S-). Analyses of bacterial 16S rRNA high-throughput sequencing data revealed increased microbial alpha diversity and decreased beta diversity in the faecal microbial profiles of S+ subjects compared to S-. Furthermore, significant differences in the abundance of several bacterial taxa were observed between samples from S+ and S- subjects, and between S+ samples collected pre- and post-anthelmintic treatment. Faecal metabolite analysis detected marked increases in the abundance of selected amino acids in S+ subjects, and of short chain fatty acids in S- subjects. Overall, our work adds valuable knowledge to current understanding of parasite-microbiota associations and will assist future mechanistic studies aimed to unravel the causality of these relationships.

Toxicological safety evaluation of freeze-dried Protaetia brevitarsis larva powder

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General toxicity and genotoxicity of freeze-dried P. brevitarsis larva powder was investigated.

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In rats, LD₅₀ and NOAEL set at >5000 and 3000 mg/kg, respectively.

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No aberrant changes in Ig E and histamine concentration were observed in the 13-week oral repeated dose study.

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No evidence of mutagenic and carcinogenic potential was observed in the genotoxicity studies.

White-spotted flower chafer (Protaetia brevitarsis) is an edible insect and its larva was used as a traditional Asian medicine. It’s a promising material as a novel food source because of its nutritional components. In this study, as part of the preclinical toxicity program, we evaluated the toxicity of freeze-dried P. brevitarsis larva powder to develop a novel food material. In a single-dose oral toxicity study in rats, there were no changes in mortality, clinical observations, and body weight in rats administered 5000 mg/kg P. brevitarsis larva powder. In a 13-week oral repeated dose toxicity study in rats, there were no adverse effects or changes in mortality, clinical observations, body weight, food consumption, ophthalmology, clinical pathology, necropsy, organ weight, and histopathology at doses of 300, 1000, and 3000 mg/kg/day. In identification of allergic reactions, P. brevitarsis larva powder induced no increases of serum immunoglobulin E and histamine concentrations over 13 weeks of oral administration in rats. In a genotoxicity assessment, P. brevitarsis larva powder didn’t provoke bacterial reverse mutations, chromosomal aberrations, and micronucleated reticulocytes. Therefore, freeze-dried P. brevitarsis larva powder shows no evidence of toxic and mutagenic changes under the experimental conditions of the present in vitro and in vivo studies.

Rendering the Intractable More Tractable: Tools from Caenorhabditis elegans Ripe for Import into Parasitic Nematodes

Recent and rapid advances in genetic and molecular tools have brought spectacular tractability to Caenorhabditis elegans, a model that was initially prized because of its simple design and ease of imaging. C. elegans has long been a powerful model in biomedical research, and tools such as RNAi and the CRISPR/Cas9 system allow facile knockdown of genes and genome editing, respectively. These developments have created an additional opportunity to tackle one of the most debilitating burdens on global health and food security: parasitic nematodes. I review how development of nonparasitic nematodes as genetic models informs efforts to import tools into parasitic nematodes. Current tools in three commonly studied parasites (Strongyloides spp., Brugia malayi, and Ascaris suum) are described, as are tools from C. elegans that are ripe for adaptation and the benefits and barriers to doing so. These tools will enable dissection of a huge array of questions that have been all but completely impenetrable to date, allowing investigation into host-parasite and parasite-vector interactions, and the genetic basis of parasitism.

Immunosuppressive PAS-1 is an excretory/secretory protein released by larval and adult worms of the ascarid nematodeAscaris suum

Helminths use several strategies to evade and/or modify the host immune response, including suppression or inactivation of the host antigen-specific response. Several helminth immunomodulatory molecules have been identified. Our studies have focused on immunosuppression induced by the roundwormAscaris suumand anA. suum-derived protein named protein 1 fromA. suum(PAS-1). Here we assessed whether PAS-1 is an excretory/secretory (E/S) protein and whether it can suppress lipopolysaccharide-induced inflammation. Larvae from infective eggs were cultured in unsupplemented Dulbecco's modified Eagle medium (DMEM) for 2 weeks. PAS-1 was then measured in the culture supernatants and in adultA. suumbody fluid at different time points by enzyme-linked immunosorbent assay (ELISA) with the monoclonal antibody MAIP-1. Secreted PAS-1 was detected in both larval culture supernatant and adult body fluid. It suppressed lipopolysaccharide (LPS)-induced leucocyte migration and pro-inflammatory cytokine production, and stimulated interleukin (IL)-10 secretion, indicating that larval and adult secreted PAS-1 suppresses inflammation in this model. Moreover, the anti-inflammatory activity of PAS-1 was abolished by treatment with MAIP-1, a PAS-1-specific monoclonal antibody, confirming the crucial role of PAS-1 in suppressing LPS-induced inflammation. These findings demonstrate that PAS-1 is an E/S protein with anti-inflammatory properties likely to be attributable to IL-10 production.

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

Eosinophil responses typify both allergic and parasitic helminth disease. In helminthic disease, the role of eosinophils can be both protective in immune responses and destructive in pathological responses. To investigate whether eosinophils are involved in both protection and pathology during filarial nematode infection, we explored the role of eosinophils and their granule proteins, eosinophil peroxidase (EPO) and major basic protein-1 (MBP-1), during infection with Brugia malayi microfilariae. Using eosinophil-deficient mice (PHIL), we further clarify the role of eosinophils in clearance of microfilariae during primary, but not challenge infection in vivo. Deletion of EPO or MBP-1 alone was insufficient to abrogate parasite clearance suggesting that either these molecules are redundant or eosinophils act indirectly in parasite clearance via augmentation of other protective responses. Absence of eosinophils increased mast cell recruitment, but not other cell types, into the broncho-alveolar lavage fluid during challenge infection. In addition absence of eosinophils or EPO alone, augmented parasite-induced IgE responses, as measured by ELISA, demonstrating that eosinophils are involved in regulation of IgE. Whole body plethysmography indicated that nematode-induced changes in airway physiology were reduced in challenge infection in the absence of eosinophils and also during primary infection in the absence of EPO alone. However lack of eosinophils or MBP-1 actually increased goblet cell mucus production. We did not find any major differences in cytokine responses in the absence of eosinophils, EPO or MBP-1. These results reveal that eosinophils actively participate in regulation of IgE and goblet cell mucus production via granule secretion during nematode-induced pathology and highlight their importance both as effector cells, as damage-inducing cells and as supervisory cells that shape both innate and adaptive immunity.

Eosinophil recruitment is a classic characteristic of both allergic and parasitic helminth diseases. Elucidation of the role of eosinophils in these diseases is of pivotal importance for understanding the mechanisms of protection and the development of pathology. In the last few years, the part played by eosinophils in helminth-defence has been dissected using in vivo models and their importance in protection has been shown to be highly specific to the host-parasite combination. This study dissects the role of eosinophils during infection with the human lymphatic filarial parasite, Brugia malayi, which causes the major neglected tropical disease, lymphatic filariasis. In particular, we study the role of the eosinophil as a double–edged sword in generating both protection and pathology. We definitively confirm the importance of eosinophils in protection against B. malayi microfilariae and show that protection is not mediated by release of the eosinophil granule proteins, major basic protein or eosinophil peroxidase alone. Overall, we reveal that during an infection with B. malayi microfilariae, eosinophils are critical for primary protective responses. However, eosinophils contribute to nematode-induced lung dysfunction, while additionally, eosinophil granules are important negative regulators of parasite-induced lung inflammatory and some adaptive immune responses.

Tolerogenic microenvironment in neonatal period induced by maternal immunization with ovalbumin

Maternal immunization with allergens, such as ovalbumin (OVA), can inhibit the development of an allergic response in offspring. The regulatory mechanisms seem to be mediated by maternal antibodies (MatAbs) and factors generated by the maternal-fetal interface. The aim of this study was to verify the pathways of inhibitory Ab transference after maternal immunization with OVA and the effect of the offspring's dendritic cells (DCs) on the generation of regulatory T (Treg) cells. We verified that preconceptional OVA immunization induces high levels of proinflammatory and regulatory cytokines in the amniotic fluid, allowing the transference of high levels of anti-OVA IgG1 Abs to the offspring. Using an adoptive nursing protocol, we verified that maternal immunization leads to MatAb transference by the placental route and by breastfeeding contribute to the inhibition of anaphylactic IgE and IgG1 Ab responses in immunized offspring. We observed that maternal immunization decreased eosinophil numbers in recovered bronchoalveolar lavage fluid and in the lung tissue, whereas with a lack of control of airway responsiveness to methacholine. Maternal immunization induced in young offspring a decreased percentage of CD11c+ DCs expressing MHC class II and CD40 molecules. Moreover, DCs from both groups of offspring when pulsed with OVA, were able to induce Treg cells in vitro. Similarly, OVA immunization at the neonatal stage increased the frequency of Treg cells, regardless of the mother's immunization status. These findings emphasize that maternal immunization leads to a complex interaction of regulatory factors, with MatAbs, DCs and Treg cells affecting the tolerance of offspring during an allergic response.

An essential role for TH2-type responses in limiting acute tissue damage during experimental helminth infection

Helminths induce potent Th2-type immune responses that can mediate worm expulsion but the importance of this response in controlling acute tissue damage caused by migrating multi-cellular parasites through vital tissues remains uncertain. We used a helminth infection model where parasitic nematode larvae migrate transiently through the lung causing damage resulting in hemorrhage and inflammation. Our findings showed initial elevations in IL-17 contributed to inflammation and lung damage while subsequent IL-4R signaling controlled IL-17 elevations, enhanced expression of insulin-like growth factor 1 and IL-10 and stimulated development of M2 cells, each of which contributed to rapid resolution of tissue damage. These studies indicate an essential role for the Th2-type immune response in mediating acute wound healing during helminth infection.

Modulation of specific and allergy-related immune responses by helminths

Helminths are master regulators of host immune responses utilising complex mechanisms to dampen host protective Th2-type responses and favour long-term persistence. Such evasion mechanisms ensure mutual survival of both the parasite and the host. In this paper, we present recent findings on the cells that are targeted by helminths and the molecules and mechanisms that are induced during infection. We discuss the impact of these factors on the host response as well as their effect in preventing the development of aberrant allergic inflammation. We also examine recent findings on helminth-derived molecules that can be used as tools to pinpoint the underlying mechanisms of immune regulation or to determine new anti-inflammatory therapeutics.

IgE cross-reactivity between Ascaris lumbricoides and mite allergens: possible influences on allergic sensitization and asthma

Nematode infections such as Ascariasis are important health problems in underdeveloped countries, most of them located in the tropics where environmental conditions also promote the perennial co-exposure to high concentrations of domestic mite allergens. Allergic diseases are common, and most of patients with asthma exhibit a predominant and strong IgE sensitization to mites. It is unknown whether co-exposure to Ascaris lumbricoides and the domestic mites Blomia tropicalis and Dermatophagoides pteronyssinus potentiates Th2 responses and IgE sensitization, thereby modifying the natural history of allergy. Recently, we obtained experimental evidence of a high cross-reactivity between the allergenic extracts of these invertebrates, involving well-known allergens such as tropomyosin and glutathione transferases. There is indirect evidence suggesting that the clinical impact of these findings may be important. In this review, we discuss the potential role of this cross-reactivity on several aspects of allergy in the tropics that have been a focus of a number of investigations, some of them with controversial results.

Effects of chronic ascariasis and trichuriasis on cytokine production and gene expression in human blood: a cross-sectional study

Background

Chronic soil-transmitted helminth (STH) infections are associated with effects on systemic immune responses that could be caused by alterations in immune homeostasis. To investigate this, we measured the impact in children of STH infections on cytokine responses and gene expression in unstimulated blood.

Methodology/Principal Findings

Sixty children were classified as having chronic, light, or no STH infections. Peripheral blood mononuclear cells were cultured in medium for 5 days to measure cytokine accumulation. RNA was isolated from peripheral blood and gene expression analysed using microarrays. Different infection groups were compared for the purpose of analysis: STH infection (combined chronic and light vs. uninfected groups) and chronic STH infection (chronic vs. combined light and uninfected groups). The chronic STH infection effect was associated with elevated production of GM-CSF (P = 0.007), IL-2 (P = 0.03), IL-5 (P = 0.01), and IL-10 (P = 0.01). Data reduction suggested that chronic infections were primarily associated with an immune phenotype characterized by elevated IL-5 and IL-10, typical of a modified Th2-like response. Chronic STH infections were associated with the up-regulation of genes associated with immune homeostasis (IDO, P = 0.03; CCL23, P = 0.008, HRK, P = 0.005), down-regulation of microRNA hsa-let-7d (P = 0.01) and differential regulation of several genes associated with granulocyte-mediated inflammation (IL-8, down-regulated, P = 0.0002; RNASE2, up-regulated, P = 0.009; RNASE3, up-regulated, p = 0.03).

Conclusions/Significance

Chronic STH infections were associated with a cytokine response indicative of a modified Th2 response. There was evidence that STH infections were associated with a pattern of gene expression suggestive of the induction of homeostatic mechanisms, the differential expression of several inflammatory genes and the down-regulation of microRNA has-let-7d. Effects on immune homeostasis and the development of a modified Th2 immune response during chronic STH infections could explain the systemic immunologic effects that have been associated with these infections such as impaired immune responses to vaccines and the suppression of inflammatory diseases.

Soil-transmitted helminth (STH or intestinal worm) infections are extremely common infectious diseases of childhood in developing countries. Infections tend be chronic and may last for many years. Chronic STH infections are associated with modulation of the immune response, a consequence of which may be a reduced prevalence of allergic inflammatory diseases such as asthma. The mechanisms by which STH infections suppress inflammatory responses are poorly understood. In this study, we hypothesized that STH infections may affect immune responses through alterations of immune homeostasis (or the steady-state adjustments of the immune system that maintain equilibrium). We investigated the capacity of blood from children classified as having no, light, or chronic STH infections to produce cytokines at rest (i.e. no immunologic stimulation) and the expression of genes in blood samples. Our data show that blood cells of children with chronic STH infections have an altered immune response that is likely to be associated with less allergic inflammation (the modified Th2 response) and that the expression of some inflammatory genes are reduced. Our findings provide insights into the mechanisms by which STH infections suppress immune responses in children to ensure the survival of the parasite and reduce inflammation.

Chronic helminth infections protect against allergic diseases by active regulatory processes

Developed countries are suffering from an epidemic rise in immunologic disorders, such as allergy-related diseases and certain autoimmunities. Several studies have demonstrated a negative association between helminth infections and inflammatory diseases (eg, allergy), providing a strong case for the involvement of helminth infections in this respect. However, some studies point in the opposite direction. The discrepancy may be explained by differences in frequency, dose, time, and type of helminth. In this review, new studies are discussed that may support the concept that chronic helminth infections in particular—but not acute infections—are associated with the expression of regulatory networks necessary for downmodulating allergic immune responses to harmless antigens. Furthermore, different components of regulatory networks are highlighted, such as the role of regulatory T and B cells, modulation of dendritic cells, early innate signals from structural cells (eg, epithelial cells), and their individual contributions to protection against allergic diseases. It is of great interest to define and characterize specific helminth molecules that have profound immunomodulatory capacities as targets for therapeutic application in the treatment or prophylaxis of allergic manifestations.

Chronic helminth infections modulate allergen-specific immune responses: Protection against development of allergic disorders?

Inflammatory diseases are on the rise in westernized countries, but also in urbanized areas of developing countries. A number of studies have now demonstrated a negative association between helminth infections and inflammatory diseases, such as allergy, suggesting a potential role for helminth-induced immune responses. However, this is not the case for all studies. In this review both supporting and opposing literature on the role of helminth infections, particularly in allergy, are discussed. Furthermore, the concept is put forward that chronic helminth infections, but not acute infections, may be associated with the expression of regulatory networks necessary for downmodulating allergic immune responses to harmless antigens. Lastly, different components of helminth-induced regulatory networks are detailed, such as the role of regulatory T and B cells, modulation of dendritic cells, the presence of suppressory alternatively activated macrophages, and their individual contributions to protection against allergic diseases. Advantage should be taken from this knowledge to identify and select individual helminth-derived molecules that may harbor therapeutic potential against inflammatory diseases.