Gastrointestinal nematode infection interferes with experimental allergic airway inflammation but not atopic dermatitis

Amelioration of ovalbumin-induced lung inflammation in a mouse model by Trichinella spiralis novel cystatin

Background and Aims

Asthma, a chronic disease affecting humans and animals, has recently become increasingly prevalent and steadily widespread. The alternative treatment of asthma using helminth infections or helminth-derived immunomodulatory molecules (IMs) has been evaluated and demonstrated significant amelioration of disease severity index in vitro and in vivo. Trichinella spiralis, a parasitic nematode and its IMs, elicits a potential to relieve asthma and other immune-related disorders. In this study, we investigated the immunomodulatory function of recombinant T. spiralis novel cystatin (rTsCstN) in ameliorating acute inflammatory asthma disorders in a murine model.

Materials and Methods

Female BALB/c mice were sensitized using intraperitoneal injection of ovalbumin (OVA)/alum and subsequently challenged with intranasal administration of OVA alone or OVA + rTsCstN for 3 consecutive days, producing OVA-induced allergic asthma models. To evaluate the therapeutic efficacy of rTsCstN, the inflammatory cells and cytokines in bronchoalveolar lavage fluid (BALF) and OVA-specific immunoglobulin E levels in serum were assessed. Histological alterations in the lung tissues were determined by hematoxylin and eosin (H&E) staining and eventually scored for the extent of inflammatory cell infiltration.

Results

The asthmatic mouse models challenged with OVA + rTsCstN demonstrated a significant reduction of eosinophils (p < 0.01), macrophages (p < 0.05), and cytokines tumor necrosis factor-α (p < 0.05) and interferon (IFN)-γ (p < 0.05) in BALF when compared with the mice challenged with OVA alone. However, the levels of interleukin (IL)-4 and IL-10 remained unchanged. Histological examination revealed that mice administered OVA + rTsCstN were less likely to have inflammatory cell infiltration in their perivascular and peribronchial lung tissues than those administered OVA alone.

Conclusion

Recombinant T. spiralis novel cystatin demonstrated immunomodulatory effects to reduce severe pathogenic alterations in asthma mouse models, encouraging a viable alternative treatment for asthma and other immunoregulatory disorders in humans and animals in the future.

The Impact of Intestinal Inflammation on Nematode's Excretory-Secretory Proteome

Parasitic nematodes and their products are promising candidates for therapeutics against inflammatory bowel diseases (IBD). Two species of nematodes, the hookworm Necator americanus and the whipworm Trichuis suis, are being used in clinical treatment trials of IBD referred to as "helminth therapy". Heligmosomoides polygyrus is a well-known model for human hookworm infections. Excretory-secretory (ES) products of H. polygyrus L4 stage that developed during colitis show a different immunomodulatory effect compared to the ES of H. polgyrus from healthy mice. The aim of the study was to evaluate excretory-secretory proteins produced by H. polygyrus L4 stage males and females that developed in the colitic milieu. Mass spectrometry was used to identify proteins. Blast2GO was used to investigate the functions of the discovered proteins. A total of 387 proteins were identified in the ES of H. polygyrus L4 males (HpC males), and 330 proteins were identified in the ES of L4 females that developed in the colitic milieu (HpC females). In contrast, only 200 proteins were identified in the ES of L4 males (Hp males) and 218 in the ES of L4 females (Hp females) that developed in control conditions. Most of the proteins (123) were detected in all groups. Unique proteins identified in the ES of HpC females included annexin, lysozyme-2, apyrase, and galectin. Venom allergen/Ancylostoma-secreted protein-like, transthyretin-like family proteins, and galectins were found in the secretome of HpC males but not in the secretome of control males. These molecules may be responsible for the therapeutic effects of nematodes in DSS-induced colitis.

Conjoint analysis of transcriptome and metabolome profiles of normal captivity and arch soil free-range in Meishan pigs

The hygiene hypothesis has been advanced as a potential explanation for the increasingly high levels of atopy and allergic disease in the general human population. In an effort to conduct a more detailed study of the link between immune activity and the hygiene hypothesis, Meishan pigs raised under normal captivity (NC) or arch soil free-range (ASF) conditions were selected as an experimental model system. Cytokine levels were found to differ significantly between these two groups consistent with a difference in cellular immune status. Integrated transcriptomic and metabolomic profiling of duodenal tissue samples from Meishan pigs were then performed, leading to the identification of differentially expressed genes (DEGs), differentially abundant metabolites (DAMs), and key pathways that were able to distinguish the NC and ASF groups. This approach led to the identification of 1,113 DEGs, as well as 577 and 372 DAMs in positive and negative ion modes, respectively. When an interaction network incorporating DEGs and metabolites associated with immune responsivity was constructed, it included factors such as 9-cis-Retinoic acid, (9Z,11E)-(13S)-13-Hydroxyoctadeca-9,11-dienoic acid and (10E,12Z)-(9S)-9-Hydroxyoctadeca-10,12-dienoic acid. Functional enrichment analyses confirmed that identified DEGs and DAMs were associated with immune-related pathways including the intestinal IgA production and PPAR signaling pathways. Together, these results offer new insight into the roles that particular genes and metabolites enriched in response to environmental stressors in free-range Meishan pigs may play in the regulation of cellular immunity, thus offering a foundation for future efforts to better understand the immunological mechanisms underlying the hygiene hypothesis.

Physiological microbial exposure transiently inhibits mouse lung ILC2 responses to allergens

Lung group 2 innate lymphoid cells (ILC2s) control the nature of immune responses to airway allergens. Some microbial products, including those that stimulate interferons, block ILC2 activation, but whether this occurs after natural infections or causes durable ILC2 inhibition is unclear. In the present study, we cohoused laboratory and pet store mice as a model of physiological microbial exposure. Laboratory mice cohoused for 2 weeks had impaired ILC2 responses and reduced lung eosinophilia to intranasal allergens, whereas these responses were restored in mice cohoused for ≥2 months. ILC2 inhibition at 2 weeks correlated with increased interferon receptor signaling, which waned by 2 months of cohousing. Reinduction of interferons in 2-month cohoused mice blocked ILC2 activation. These findings suggest that ILC2s respond dynamically to environmental cues and that microbial exposures do not control long-term desensitization of innate type 2 responses to allergens.

Suppression of airway allergic eosinophilia by Hp-TGM, a helminth mimic of TGF-β

Type 2-high asthma is a chronic inflammatory disease of the airways which is increasingly prevalent in countries where helminth parasite infections are rare, and characterized by T helper 2 (Th2)-dependent accumulation of eosinophils in the lungs. Regulatory cytokines such as TGF-β can restrain inflammatory reactions, dampen allergic Th2 responses, and control eosinophil activation. The murine helminth parasite Heligmosomoides polygyrus releases a TGF-β mimic (Hp-TGM) that replicates the biological and functional properties of TGF-β despite bearing no structural similarity to the mammalian protein. Here, we investigated if Hp-TGM could alleviate allergic airway inflammation in mice exposed to Alternaria alternata allergen, house dust mite (HDM) extract or alum-adjuvanted ovalbumin protein (OVA). Intranasal administration of Hp-TGM during Alternaria exposure sharply reduced airway and lung tissue eosinophilia along with bronchoalveolar lavage fluid IL-5 and lung IL-33 cytokine levels at 24 h. The protective effect of Hp-TGM on airway eosinophilia was also obtained in the longer T-cell mediated models of HDM or OVA sensitisation with significant inhibition of eotaxin-1, IL-4 and IL-13 responses depending on the model and time-point. Hp-TGM was also protective when administered parenterally either when given at the time of allergic sensitisation or during airway allergen challenge. This project has taken the first steps in identifying the role of Hp-TGM in allergic asthma and highlighted its ability to control lung inflammation and allergic pathology. Future research will investigate the mode of action of Hp-TGM against airway allergic eosinophilia, and further explore its potential to be developed as a biotherapeutic in allergic asthma.

NAD(P)H fluorescence lifetime imaging of live intestinal nematodes reveals metabolic crosstalk between parasite and host

Infections with intestinal nematodes have an equivocal impact: they represent a burden for human health and animal husbandry, but, at the same time, may ameliorate auto-immune diseases due to the immunomodulatory effect of the parasites. Thus, it is key to understand how intestinal nematodes arrive and persist in their luminal niche and interact with the host over long periods of time. One basic mechanism governing parasite and host cellular and tissue functions, metabolism, has largely been neglected in the study of intestinal nematode infections. Here we use NADH (nicotinamide adenine dinucleotide) and NADPH (nicotinamide adenine dinucleotide phosphate) fluorescence lifetime imaging of explanted murine duodenum infected with the natural nematode Heligmosomoides polygyrus and define the link between general metabolic activity and possible metabolic pathways in parasite and host tissue, during acute infection. In both healthy and infected host intestine, energy is effectively produced, mainly via metabolic pathways resembling oxidative phosphorylation/aerobic glycolysis features. In contrast, the nematodes shift their energy production from balanced fast anaerobic glycolysis-like and effective oxidative phosphorylation-like metabolic pathways, towards mainly anaerobic glycolysis-like pathways, back to oxidative phosphorylation/aerobic glycolysis-like pathways during their different life cycle phases in the submucosa versus the intestinal lumen. Additionally, we found an increased NADPH oxidase (NOX) enzymes-dependent oxidative burst in infected intestinal host tissue as compared to healthy tissue, which was mirrored by a similar defense reaction in the parasites. We expect that, the here presented application of NAD(P)H-FLIM in live tissues constitutes a unique tool to study possible shifts between metabolic pathways in host-parasite crosstalk, in various parasitic intestinal infections.

Profiles of CD4+, CD8+, and regulatory T cells and circulating cytokines in hookworm-infected children in southern Thailand

Hookworm infection is the most common human helminthic infection in the rural areas of southern Thailand. There is little information on the induced cellular immune responses in hookworm-infected children. The present study aimed to investigate the cellular immune responses, regulatory T cells (Tregs), Th1-type cytokines (interleukin (IL)-2 and interferon (IFN)-γ), a Th2-type cytokine (IL-5) and IL-10, which is one of the cytokines secreted by Tregs in hookworm-infected children. Twenty-nine schoolchildren diagnosed with hookworm infections and 28 healthy controls were enrolled in the study. CD4+ and CD8+ T cells and Tregs in whole blood were analyzed using flow cytometry. Plasma IL-2, IL-5, IL-10 and IFN-γ concentrations were quantified by enzyme-linked immunosorbent assay (ELISA). The median CD4+ T cell frequency was significantly higher in hookworm-infected children than healthy controls. Compared to healthy controls, hookworm-infected children had a significantly increased absolute number of Tregs. No differences in circulating CD8+ T cell median frequency or absolute numbers were observed among hookworm-infected children or healthy controls. Elevated IL-2 and IL-10 concentrations were found in hookworm-infected children. Moreover, the absolute number of Tregs was significantly positively correlated with the plasma IL-10 concentration (r_s = 0.406, P = 0.029). This study showed that hookworm-infected schoolchildren had significantly different immune responses than healthy controls, including an increase in the CD4+ T cell number, a significant induction of Tregs and significantly elevated circulating IL-10 levels. These alterations could be the mechanism underlying the immunomodulation that alleviates allergic diseases among hookworm-infected individuals.

Mycobacterium-Induced Th1, Helminths-Induced Th2 Cells and the Potential Vaccine Candidates for Allergic Asthma: Imitation of Natural Infection

Bronchial asthma is one of the most chronic pulmonary diseases and major public health problems. In general, asthma prevails in developed countries than developing countries, and its prevalence is increasing in the latter. For instance, the hygiene hypothesis demonstrated that this phenomenon resulted from higher household hygienic standards that decreased the chances of infections, which would subsequently increase the occurrence of allergy. In this review, we attempted to integrate our knowledge with the hygiene hypothesis into beneficial preventive approaches for allergic asthma. Therefore, we highlighted the studies that investigated the correlation between allergic asthma and the two different types of infections that induce the two major antagonizing arms of T cells. This elucidation reflects the association between various types of natural infections and the immune system, which is predicted to support the main objective of the current research on investigating of the benefits of natural infections, regardless their immune pathways for the prevention of allergic asthma. We demonstrated that natural infection with Mycobacterium tuberculosis (Mtb) prevents the development of allergic asthma, thus Bacille Calmette-Guérin (BCG) vaccine is suggested at early age to mediate the same prevention particularly with increasing its efficiency through genetic engineering-based modifications. Likewise, natural helminth infections might inhabit the allergic asthma development. Therefore, helminth-derived proteins at early age are good candidates for designing vaccines for allergic asthma and it requires further investigation. Finally, we recommend imitation of natural infections as a general strategy for preventing allergic asthma that increased dramatically over the past decades.

Trilateral Relationship: Ascaris, Microbiota, and Host Cells

Ascariasis is a globally spread intestinal nematode infection of humans and a considerable concern in pig husbandry. Ascaris accomplishes a complex body migration from the intestine via the liver and lung before returning to the intestine. Tissue migration and the habitat shared with a complex microbial community pose the question of how the nematode interacts with microbes and host cells from various tissues. This review addresses the current knowledge of the trilateral relationship between Ascaris, its microbial environment, and host cells, and discusses novel approaches targeting these interactions to combat this widespread infection of livestock and man.

What Can Parasites Tell Us About the Pathogenesis and Treatment of Asthma and Allergic Diseases

The same mechanisms that enable host defense against helminths also drive allergic inflammation. This suggests that pathomechanisms of allergic diseases represent evolutionary old responses against helminth parasites and that studying antihelminth immunity may provide insights into pathomechanisms of asthma. However, helminths have developed an intricate array of immunoregulatory mechanisms to modulate type 2 immune mechanisms. This has led to the hypothesis that the lack of helminth infection may contribute to the rise in allergic sensitization in modern societies. Indeed, the anti-inflammatory potential of helminth (worm) parasites and their products in allergy and asthma has been recognized for decades. As helminth infections bring about multiple undesired effects including an increased susceptibility to other infections, intended helminth infection is not a feasible approach to broadly prevent or treat allergic asthma. Thus, the development of new helminth-based biopharmaceutics may represent a safer approach of harnessing type 2–suppressive effects of helminths. However, progress regarding the mechanisms and molecules that are employed by helminths to modulate allergic inflammation has been relatively recent. The scavenging of alarmins and the modulation of lipid mediator pathways and macrophage function by helminth proteins have been identified as important immunoregulatory mechanisms targeting innate immunity in asthma and allergy. In addition, by regulating the activation of dendritic cells and by promoting regulatory T-cell responses, helminth proteins can counterregulate the adaptive T helper 2 cell response that drives allergic inflammation. Despite these insights, important open questions remain to be addressed before helminth molecules can be used for the prevention and treatment of asthma and other allergic diseases.

The Gastrointestinal Helminth Heligmosomoides bakeri Suppresses Inflammation in a Model of Contact Hypersensitivity

Helminths regulate host immune responses to ensure their own long-term survival. Numerous studies have demonstrated that these helminth-induced regulatory mechanisms can also limit host inflammatory responses in several disease models. We used the Heligmosomoides bakeri (Hb) infection model (also known as H. polygyrus or H. polygyrus bakeri in the literature) to test whether such immune regulation affects skin inflammatory responses induced by the model contact sensitiser dibutyl phthalate fluorescein isothiocynate (DBP-FITC). Skin lysates from DBP-FITC-sensitized, Hb-infected mice produced less neutrophil specific chemokines and had significantly reduced levels of skin thickening and cellular inflammatory responses in tissue and draining lymph nodes (LNs) compared to uninfected mice. Hb-induced suppression did not appear to be mediated by regulatory T cells, nor was it due to impaired dendritic cell (DC) activity. Mice cleared of infection remained unresponsive to DBP-FITC sensitization indicating that suppression was not via the secretion of Hb-derived short-lived regulatory molecules, although long-term effects on cells cannot be ruled out. Importantly, similar helminth-induced suppression of inflammation was also seen in the draining LN after intradermal injection of the ubiquitous allergen house dust mite (HDM). These findings demonstrate that Hb infection attenuates skin inflammatory responses by suppressing chemokine production and recruitment of innate cells. These findings further contribute to the growing body of evidence that helminth infection can modulate inflammatory and allergic responses via a number of mechanisms with potential to be exploited in therapeutic and preventative strategies in the future.

Regulatory T-cells in helminth infection: induction, function and therapeutic potential

Helminth parasites infect an alarmingly large proportion of the world's population, primarily within tropical regions, and their ability to down‐modulate host immunity is key to their persistence. Helminths have developed multiple mechanisms that induce a state of hyporesponsiveness or immune suppression within the host; of particular interest are mechanisms that drive the induction of regulatory T‐cells (Tregs). Helminths actively induce Tregs either directly by secreting factors, such as the TGF‐β mimic Hp‐TGM, or indirectly by interacting with bystander cell types such as dendritic cells and macrophages that then induce Tregs. Expansion of Tregs not only enhances parasite survival but, in cases such as filarial infection, Tregs also play a role in preventing parasite‐associated pathologies. Furthermore, Tregs generated during helminth infection have been associated with suppression of bystander immunopathologies in a range of inflammatory conditions such as allergy and autoimmune disease. In this review, we discuss evidence from natural and experimental infections that point to the pathways and molecules involved in helminth Treg induction, and postulate how parasite‐derived molecules and/or Tregs might be applied as anti‐inflammatory therapies in the future.

Regulation of immunity and allergy by helminth parasites

There is increasing interest in helminth parasite modulation of the immune system, both from the fundamental perspective of the "arms race" between host and parasite, and equally importantly, to understand if parasites offer new pathways to abate and control untoward immune responses in humans. This article reviews the epidemiological and experimental evidence for parasite down-regulation of host immunity and immunopathology, in allergy and other immune disorders, and recent progress towards defining the mechanisms and molecular mediators which parasites exploit in order to modulate their host. Among these are novel products that interfere with epithelial cell alarmins, dendritic cell activation, macrophage function and T-cell responsiveness through the promotion of an immunoregulatory environment. These modulatory effects assist parasites to establish and survive, while dampening immune reactivity to allergens, autoantigens and microbiome determinants.

Adoptive transfer of Trichinella spiralis-activated macrophages can ameliorate both Th1- and Th2-activated inflammation in murine models

Trichinella spiralis is a zoonotic nematode and food borne parasite and infection with T. spiralis leads to suppression of the host immune response and other immunopathologies. Alternative activated macrophages (M2) as well as T_reg cells, a target for immunomodulation by the helminth parasite, play a critical role in initiating and modulating the host immune response to parasite. The precise mechanism by which helminths modulate host immune response is not fully understood. To determine the functions of parasite-induced M2 macrophages, we compared the effects of M1 and M2 macrophages obtained from Trichinella spiralis-infected mice with those of T. spiralis excretory/secretory (ES) protein-treated macrophages on experimental intestinal inflammation and allergic airway inflammation. T. spiralis infection induced M2 macrophage polarization by increasing the expression of CD206, ARG1, and Fizz2. In a single application, we introduced macrophages obtained from T. spiralis-infected mice and T. spiralis ES protein-treated macrophages into mice tail veins before the induction of dextran sulfate sodium (DSS)-induced colitis, ovalbumin (OVA)-alum sensitization, and OVA challenge. Colitis severity was assessed by determining the severity of colitis symptoms, colon length, histopathologic parameters, and Th1-related inflammatory cytokine levels. Compared with the DSS-colitis group, T. spiralis-infected mice and T. spiralis ES protein-treated macrophages showed significantly lower disease activity index (DAI) at sacrifice and smaller reductions of body weight and proinflammatory cytokine level. The severity of allergic airway inflammation was assessed by determining the severity of symptoms of inflammation, airway hyperresponsiveness (AHR), differential cell counts, histopathologic parameters, and levels of Th2-related inflammatory cytokines. Severe allergic airway inflammation was induced after OVA-alum sensitization and OVA challenge, which significantly increased Th2-related cytokine levels, eosinophil infiltration, and goblet cell hyperplasia in the lung. However, these severe allergic symptoms were significantly decreased in T. spiralis-infected mice and T. spiralis ES protein-treated macrophages. Helminth infection and helminth ES proteins induce M2 macrophages. Adoptive transfer of macrophages obtained from helminth-infected mice and helminth ES protein-activated macrophages is an effective treatment for preventing and treating airway allergy in mice and is promising as a therapeutic for treating inflammatory diseases.

Helminth-induced regulatory T cells and suppression of allergic responses

Infection with helminths has been associated with lower rates of asthma and other allergic diseases. This has been attributed, in part, to the ability of helminths to induce regulatory T cells that suppress inappropriate immune responses to allergens. Recent compelling evidence suggests that helminths may promote regulatory T cell expansion or effector functions through either direct (secretion of excretory/secretory molecules) or indirect mechanisms (regulation of the microbiome). This review will discuss key findings from human immunoepidemiological observations, studies using animal models of disease, and clinical trials with live worm infections, discussing the therapeutic potential for worms and their secreted products for treating allergic inflammation.

IRF-8 regulates expansion of myeloid-derived suppressor cells and Foxp3+ regulatory T cells and modulates Th2 immune responses to gastrointestinal nematode infection

Interferon regulatory factor-8 (IRF-8) is critical for Th1 cell differentiation and negatively regulates myeloid cell development including myeloid-derived suppressor cells (MDSC). MDSC expand during infection with various pathogens including the gastrointestinal (GI) nematode Heligmosomoides polygyrus bakeri (Hpb). We investigated if IRF-8 contributes to Th2 immunity to Hpb infection. Irf8 expression was down-regulated in MDSC from Hpb-infected C57BL/6 (B6) mice. IRF-8 deficient Irf8^-/- and BXH-2 mice had significantly higher adult worm burdens than B6 mice after primary or challenge Hpb infection. During primary infection, MDSC expanded to a significantly greater extent in mesenteric lymph nodes (MLN) and spleens of Irf8^-/- and BXH-2 than B6 mice. CD4⁺GATA3⁺ T cells numbers were comparable in MLN of infected B6 and IRF-8 deficient mice, but MLN cells from infected IRF-8 deficient mice secreted significantly less parasite-specific IL-4 ex vivo. The numbers of alternatively activated macrophages in MLN and serum levels of Hpb-specific IgG1 and IgE were also significantly less in infected Irf8^-/- than B6 mice. The frequencies of antigen-experienced CD4⁺CD11a^hiCD49d^hi cells that were CD44^hiCD62L^- were similar in MLN of infected Irf8^-/- and B6 mice, but the proportions of CD4⁺GATA3⁺ and CD4⁺IL-4⁺ T cells were lower in infected Irf8^-/- mice. CD11b⁺Gr1⁺ cells from naïve or infected Irf8^-/- mice suppressed CD4⁺ T cell proliferation and parasite-specific IL-4 secretion in vitro albeit less efficiently than B6 mice. Surprisingly, there were significantly more CD4⁺ T cells in infected Irf8^-/- mice, with a higher frequency of CD4⁺CD25⁺Foxp3⁺ T (Tregs) cells and significantly higher numbers of Tregs than B6 mice. In vivo depletion of MDSC and/or Tregs in Irf8^-/- mice did not affect adult worm burdens, but Treg depletion resulted in higher egg production and enhanced parasite-specific IL-5, IL-13, and IL-6 secretion ex vivo. Our data thus provide a previously unrecognized role for IRF-8 in Th2 immunity to a GI nematode.

We investigated if IRF-8, which is critical for Th1 immunity and negatively regulates myeloid cell development including MDSC, contributes to Th2 immunity to the gastrointestinal nematode Heligmosomoides polygyrus bakeri (Hpb). Irf8 expression was down-regulated in MDSC from infected C57BL/6 (B6) mice. Hpb-infected IRF-8 deficient mice had significantly higher adult worm burdens than B6 mice. There were significantly more MDSC, fewer alternatively activated macrophages, lower serum levels of Hpb-specific antibodies in infected IRF-8 deficient than B6 mice, and MLN cells from infected IRF-8 deficient mice secreted less parasite-specific IL-4 ex vivo. There were similar frequencies of antigen-experienced CD4⁺CD11a^hiCD49d^hi T cells in MLN that were CD44^hiCD62L^- in infected Irf8^-/- and B6 mice, but lower proportions of CD4⁺GATA3⁺ and CD4⁺IL-4⁺ T cells in Irf8^-/- mice. Infected Irf8^-/- mice had a higher frequency of CD4⁺Foxp3⁺ T (Tregs) cells and significantly higher numbers of Tregs compared to infected B6 mice. MDSC from infected Irf8^-/- mice suppressed CD4⁺ T cell effector functions in vitro albeit less efficiently than B6 mice. Treg and/or MDSC depletion did not affect adult worm burdens in infected Irf8^-/- mice, but Treg depletion partially restored Th2 cytokine responses. These data highlight the importance of IRF-8 in Th2 immunity to Hpb infection.

Immune responses to fungal aeroallergen in Heligmosomoides polygyrus-infected mice vary by age

Parasite infections in the developing world have been considered to promote resistance to immune-mediated diseases such as asthma. Mouse studies have shown that helminths and their products reduce the development of allergic asthma. Since epidemiologic studies that show similar protection are in relation to geohelminth infections that occur in early life, we hypothesized that the parasite-mediated protection against asthma may differ by age. Mice infected with Heligmosomoides polygyrus at 3-weeks of age had similar asthma phenotype compared to mice infected at 28-weeks of age wherein airway eosinophilia was unaltered but tissue inflammation and GC metaplasia were reduced. In contrast, mice infected at 18-weeks of age had elevated macrophagic airway inflammation with accompanying tissue pathology. The presence of γδ T cells and T_reg cells in the airways was also regulated by age at worm infection. Our findings demonstrate the importance of age in immune responses that may regulate gut and lung diseases.

The Helminth-Derived Immunomodulator AvCystatin Reduces Virus Enhanced Inflammation by Induction of Regulatory IL-10+ T Cells

Respiratory Syncytial Virus (RSV) is a major pathogen causing low respiratory tract disease (bronchiolitis), primarily in infants. Helminthic infections may alter host immune responses to both helminths and to unrelated immune triggers. For example, we have previously shown that filarial cystatin (AvCystatin/Av17) ameliorates allergic airway inflammation. However, helminthic immunomodulators have so far not been tested in virus-induced disease. We now report that AvCystatin prevents Th2-based immunopathology in vaccine-enhanced RSV lung inflammation, a murine model for bronchiolitis. AvCystatin ablated eosinophil influx, reducing both weight loss and neutrophil recruitment without impairing anti-viral immune responses. AvCystatin also protected mice from excessive inflammation following primary RSV infection, significantly reducing neutrophil influx and cytokine production in the airways. Interestingly, we found that AvCystatin induced an influx of CD4⁺ FoxP3⁺ interleukin-10-producing T cells in the airway and lungs, correlating with immunoprotection, and the corresponding cells could also be induced by adoptive transfer of AvCystatin-primed F4/80⁺ macrophages. Thus, AvCystatin ameliorates enhanced RSV pathology without increasing susceptibility to, or persistence of, viral infection and warrants further investigation as a possible therapy for virus-induced airway disease.

Exosome-transported microRNAs of helminth origin: new tools for allergic and autoimmune diseases therapy?

Chronic diseases associated with inflammation show fast annual increase in their incidence. This has been associated with excessive hygiene habits that limit contacts between the immune system and helminth parasites. Helminthic infections induce regulation and expansion of regulatory T cells (Treg) leading to atypical Th2 type immune responses, with downregulation of the inflammatory component usually associated with these type of responses. Many cells, including those of the immune system, produce extracellular vesicles called exosomes which mediate either immune stimulation (DCs) or immune modulation (T cells). The transfer of miRNAs contained in T-cell exosomes has been shown to contribute to downregulate the production of inflammatory mediators. It has been recently described the delivery to the host-parasite interface of exosomes containing miRNAs by helminths and its internalization by host cells. In this sense, helminth microRNAs transported in exosomes and internalized by immune host cells exert an important role in the expansion of Treg cells, resulting in the control of inflammation. We here provide relevant information obtained in the field of exosomes, cell-cell communication and miRNAs, showing the high potential of helminth miRNAs delivered in exosomes to host cells as new therapeutic tools against diseases associated with exacerbated inflammatory responses.

Cultivation of Heligmosomoides polygyrus: an immunomodulatory nematode parasite and its secreted products

Heligmosomoides polygyrus (formerly known as Nematospiroides dubius, and also referred to by some as H. bakeri) is a gastrointestinal helminth that employs multiple immunomodulatory mechanisms to establish chronic infection in mice and closely resembles prevalent human helminth infections. H. polygyrus has been studied extensively in the field of helminth-derived immune regulation and has been found to potently suppress experimental models of allergy and autoimmunity (both with active infection and isolated secreted products). The protocol described in this paper outlines management of the H. polygyrus life cycle for consistent production of L3 larvae, recovery of adult parasites, and collection of their excretory-secretory products (HES).

Prevention of mother-to-child transmission of HIV in rural Uganda: modelling effectiveness and impact of scaling-up PMTCT services

Background

The reported coverage of any antiretroviral (ARV) prophylaxis for prevention of mother-to-child transmission (PMTCT) has increased in sub-Saharan Africa in recent years, but was still only 60% in 2010. However, the coverage estimate is subject to overestimations since it only considers enrolment and not completion of the PMTCT programme. The PMTCT programme is complex as it builds on a cascade of sequential interventions that should take place to reduce mother-to-child transmission (MTCT) of HIV: starting with antenatal care (ANC), HIV testing, and ARVs for the woman and the baby.

Objective

The objective was to estimate the number of children infected with HIV in a district population, using empirical data on uptake of PMTCT components combined with data on MTCT rates.

Design

This study is based on a population-based cohort of pregnant women recruited in the Iganga-Mayuge Health and Demographic Surveillance Site in rural Uganda 2008–2010. We later modelled different scenarios assuming increased uptake of specific PMTCT components to estimate the impact on MTCT for each scenario.

Results

In this setting, HIV infections in children could be reduced by 28% by increasing HIV testing capacity at health facilities to ensure 100% testing among women seeking ANC. Providing ART to all women who received ARV prophylaxis would give an 18% MTCT reduction.

Conclusions

Our results highlight the urgency in scaling-up universal access to HIV testing at all ANC facilities, and the potential gains of early enrolment of all pregnant women on antiretroviral treatment for PMTCT. Further, to determine the effectiveness of PMTCT programmes in different settings, it is crucial to analyse at what stages of the PMTCT cascade that dropouts occur to target interventions accordingly.

Induction of regulatory cells by helminth parasites: exploitation for the treatment of inflammatory diseases

Helminth parasites are highly successful pathogens, chronically infecting a quarter of the world's population, causing significant morbidity but rarely causing death. Protective immunity and expulsion of helminths is mediated by T-helper 2 (Th2) cells, type 2 (M2) macrophages, type 2 innate lymphoid cells, and eosinophils. Failure to mount these type 2 immune responses can result in immunopathology mediated by Th1 or Th17 cells. Helminths have evolved a wide variety of approaches for immune suppression, especially the generation of regulatory T cells and anti-inflammatory cytokines interleukin-10 and transforming growth factor-β. This is a very effective strategy for subverting protective immune responses to prolong their survival in the host but has the bystander effect of modulating immune responses to unrelated antigens. Epidemiological studies in humans have shown that infection with helminth parasites is associated with a low incidence of allergy/asthma and autoimmunity in developing countries. Experimental studies in mice have demonstrated that regulatory immune responses induced by helminth can suppress Th2 and Th1/Th17 responses that mediate allergy and autoimmunity, respectively. This has provided a rational explanation of the 'hygiene hypothesis' and has also led to the exploitation of helminths or their immunomodulatory products in the development of new immunosuppressive therapies for inflammatory diseases in humans.

Worms as therapeutic agents for allergy and asthma: understanding why benefits in animal studies have not translated into clinical success

Helminth infections are associated with decreased rates of autoimmunity and allergy, and several clinical studies have demonstrated that intentional infection with helminths can reduce symptoms of autoimmune diseases. In contrast, though numerous animal studies have demonstrated that helminth infections ameliorate allergic diseases, clinical trials in humans have not shown benefit. In this article, we review in detail the 2 human studies that have prospectively tested whether helminth infections protect against allergy. We next review the research designs and results obtained from animal studies, and compare these to the human trials. We then postulate possible reasons for the lack of efficacy observed in clinical trials to date and discuss potential future areas of research in this field.

Microorganism-induced suppression of allergic airway disease: novel therapies on the horizon?

Allergic airway disease is a major global health burden, and novel treatment options are urgently needed. Numerous epidemiological and experimental studies suggest that certain helminths and bacteria protect against respiratory allergies. These microorganisms are strong regulators of the immune system, and various potential regulatory mechanisms by which they protect against allergic airway inflammation have been proposed. Whereas early studies addressed the beneficial effect of natural infections, the focus now shifts toward identifying the dominant protective molecules and exploring their efficacy in models of allergic airway disease. In this article, we will review the evidence for microbe-mediated protection from allergic airway disease, the potential modes of action involved and discuss advances as well as limitations in the translation of this knowledge into novel treatment strategies against allergic airway disease.

Subsets of regulatory T cells and their roles in allergy

In recent years, it is recognized that acquired immunity is controlled by regulatory T cell (Treg). Since fundamental pathophysiological changes of allergy are mainly caused by hyperresponsiveness of immune system to allergens that acquires after birth, Tregs likely play key roles in the pathogenesis of allergy, particularly during the sensitization phase. However, accumulated information indicate that there are several distinctive subtypes of Tregs in man, and each of them seems to play different role in controlling immune system, which complicates the involvement of Tregs in allergy. The aim of the present study is to attempt to classify subtypes of Tregs and summarize their roles in allergy. Tregs should include natural Tregs (nTreg) including inducible costimulator (ICOS)(+) Tregs, inducible/adaptive Tregs (iTreg), interleukin (IL)-10-producing type 1 Tregs (Tr1 cells), CD8(+) Tregs and IL-17-producing Tregs. These cells share some common features including expression of Foxp3 (except for Tr1 cells), and secretion of inhibitory cytokine IL-10 and/or TGF-β. Furthermore, it is noticeable that Tregs likely contribute to allergic disorders such as dermatitis and airway inflammation, and play a crucial role in the treatment of allergy through their actions on suppression of effector T cells and inhibition of activation of mast cells and basophils. Modulation of functions of Tregs may provide a novel strategy to prevent and treat allergic diseases.

Prevalence of and risk factors for the development of atopic dermatitis in schoolchildren aged 12-14 in northwest Croatia

BACKGROUND

Atopic dermatitis is a common allergic disorder. A multifactorial background for atopic dermatitis has been suggested, with genetic as well as environmental factors influencing disease development. Our aim was to estimate the prevalence rate and associated factors for atopic dermatitis in northern Croatia using the methods of the internationally standardised ISAAC protocol.

METHODS

The study was undertaken among 12-14-year-old schoolchildren. Data were collected using standardised ISAAC written questionnaire Phase One and some selected questions from the ISAAC supplementary questionnaire completed by parents.

RESULTS

A total of 2887 children participated in the study. Estimated lifetime (ever) prevalence rate of atopic dermatitis symptoms was 7.55% and estimated 12-month prevalence rate was 5.75%. The factors found to be associated to the symptoms of atopic dermatitis ever were: positive family atopy, female gender, sleeping on feather pillow and contact with pets after age of seven, and to the symptoms in the past 12 months were: positive family atopy, female gender, sleeping on feather pillow, parasite infestation, and contact with pets in the first year of life.

CONCLUSIONS

The results of our study show that northern Croatia is a region with moderate prevalence rates of atopic dermatitis. Following risk factors were family atopy, female gender and sleeping on feather pillow. Because of controversial results of previous studies conducted on the same topic further investigations should be made.

Allergic diseases and helminth infections

The relationships between allergic diseases and helminth infections are inconsistent. Some studies have suggested that helminth infections induce or increase the severity of atopic diseases. Other studies report that children infected with some helminths have lower prevalence and milder atopic symptoms. Expanding our knowledge on the mechanism of immunological modification as a result of helminth infection, and understanding the interaction between helminth infections and allergic diseases will be useful for developing potentially new treatments using some helminths, and for evaluating the risks and benefits of eradicating helminth infections in endemic areas. This article reviews current knowledge on the mechanisms of allergic disease, the immunological modifications that result from helminth infections, and clinical evidence of the effects of these infections on allergic diseases.

Prerequisites for the pharmaceutical industry to develop and commercialise helminths and helminth-derived product therapy

During the past 10 years, immunologists, epidemiologists and parasitologists have made many new exciting discoveries in the field of helminth-mediated immune regulation. In addition, many animal experiments have shown that certain helminths or products derived from helminths can protect mice from developing allergic or autoimmune disease. Some clinical trials utilising Trichuris suis or Necator americanus for the treatment of allergic disorders and inflammatory bowel disease have been conducted. The outcomes of these trials suggest that they may be used to treat these disorders. However, to date no helminth therapy is routinely being applied to patients and no helminth-derived product therapy has been developed. In order to bring new drugs to the market and shoulder the enormous costs involved in developing such therapies, pharmaceutical companies need to be involved. However, currently the resources from the pharmaceutical industry devoted to this concept are relatively small and there are good reasons why the industry may have been reluctant to invest in developing these types of therapies. In this review article, the hurdles that must be overcome before the pharmaceutical industry might invest in these novel therapies are outlined.

Immunity to the model intestinal helminth parasite Heligmosomoides polygyrus

Heligmosomoides polygyrus is a natural intestinal parasite of mice, which offers an excellent model of the immunology of gastrointestinal helminth infections of humans and livestock. It is able to establish long-term chronic infections in many strains of mice, exerting potent immunomodulatory effects that dampen both protective immunity and bystander reactions to allergens and autoantigens. Immunity to the parasite develops naturally in some mouse strains and can be induced in others through immunization; while the mechanisms of protective immunity are not yet fully defined, both antibodies and a host cellular component are required, with strongest evidence for a role of alternatively activated macrophages. We discuss the balance between resistance and susceptibility in this model system and highlight new themes in innate and adaptive immunity, immunomodulation, and regulation of responsiveness in helminth infection.

Nematode modulation of inflammatory bowel disease

Inflammatory bowel disease (IBD) is a chronic disease arising due to a culmination of genetic, environmental, and lifestyle-associated factors and resulting in an excessive pro-inflammatory response to bacterial populations in the gastrointestinal tract. The prevalence of IBD in developing nations is relatively low, and it has been proposed that this is directly correlated with a high incidence of helminth infections in these areas. Gastrointestinal nematodes are the most prevalent parasitic worms, and they efficiently modulate the immune system of their hosts in order to establish chronic infections. Thus, they may be capable of suppressing unrelated inflammation in disorders such as IBD. This review describes how nematodes, or their products, suppress innate and adaptive pro-inflammatory immune responses and how the mechanisms involved in the induction of anti-nematode responses regulate colitis in experimental models and clinical trials with IBD patients. We also discuss how refinement of nematode-derived therapies should ultimately result in the development of potent new therapeutics of clinical inflammatory disorders.

Helminth infections and host immune regulation

Helminth parasites infect almost one-third of the world's population, primarily in tropical regions. However, regions where helminth parasites are endemic record much lower prevalences of allergies and autoimmune diseases, suggesting that parasites may protect against immunopathological syndromes. Most helminth diseases are spectral in nature, with a large proportion of relatively asymptomatic cases and a subset of patients who develop severe pathologies. The maintenance of the asymptomatic state is now recognized as reflecting an immunoregulatory environment, which may be promoted by parasites, and involves multiple levels of host regulatory cells and cytokines; a breakdown of this regulation is observed in pathological disease. Currently, there is much interest in whether helminth-associated immune regulation may ameliorate allergy and autoimmunity, with investigations in both laboratory models and human trials. Understanding and exploiting the interactions between these parasites and the host regulatory network are therefore likely to highlight new strategies to control both infectious and immunological diseases.

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.

Experimental autoimmune encephalomyelitis evolution was not modified by multiple infections with Strongyloides venezuelensis

According to the hygiene hypothesis, the increased incidence of allergic and autoimmune diseases in developed countries is mainly explained by the decreased contact between the human population and certain environmental agents as lactobacillus, mycobacteria and helminths. In this study, we evaluated the effect of multiple infections with Strongyloides venezuelensis on the development of experimental autoimmune encephalomyelitis (EAE) in Lewis rats. Multiple infections before EAE induction were not able to change the evolution of the disease. No alterations were observed in weight loss, clinical score and inflammation intensity at the central nervous system. The presence of significant levels of parasite-specific IgG1 but not IgG2b suggested a Th2 polarization. However, the percentage and absolute number of CD4+CD25+Foxp3+ T cells were not changed, being their levels in the spleen and lymph nodes of infected rats comparable to the ones found in normal animals. These results suggest that a Th2-polarized response without concomitant expansion of Foxp3+ regulatory T cells was not able to modify EAE progression. Even though these results do not threaten the hygiene hypothesis, they suggest that this paradigm might be an oversimplification. They also emphasize the need of a study to compare the immunoregulatory ability associated with different helminth spp.

Developments in the field of allergy in 2009 through the eyes of Clinical and Experimental Allergy

In 2009 the journal published in the region of 200 papers including reviews, editorials, opinion pieces and original papers that ran the full gamut of allergic disease. It is instructive to take stock of this output to determine patterns of interest and where the cutting edge lies. We have surveyed the field of allergic disease as seen through the pages of Clinical and Experimental Allergy (CEA) highlighting trends, emphasizing notable observations and placing discoveries in the context of other key papers published during the year. The review is divided into similar sections as the journal. In the field of Asthma and Rhinitis CEA has contributed significantly to the debate about asthma phenotypes and expressed opinions about the cause of intrinsic asthma. It has also added its halfpennyworth to the hunt for meaningful biomarkers. In Mechanisms the considerable interest in T cell subsets including Th17 and T regulatory cells continues apace and the discipline of Epidemiology continues to invoke a steady stream of papers on risk factors for asthma with investigators still trying to explain the post-second world war epidemic of allergic disease. Experimental Models continue to make important contributions to our understanding of pathogenesis of allergic disease and in the Clinical Allergy section various angles on immunotherapy are explored. New allergens continue to be described in the allergens section to make those allergen chips even more complicated. A rich and vibrant year helpfully summarized by some of our associate editors.

Glycomarkers in parasitic infections and allergy

Both helminth infections and contact with allergens result in development of a Th2 type of immune response in the affected individual. In this context, the hygiene hypothesis suggests that reduced prevalence of parasitic infections and successful vaccination strategies are causative for an increase of allergies in industrialized countries. It is therefore of interest to study glycans and their role as immunogenic structures in both parasitic infections and allergies. In the present paper we review information on the different types of glycan structure present in proteins from plant and animal food, insect venom and helminth parasites, and their role as diagnostic markers. In addition, the application of these glycan structures as immunomodulators in novel immunotherapeutic strategies is discussed.

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.

Establishment of nematode infection despite increased Th2 responses and immunopathology after selective depletion of Foxp3+ cells

Here, we show that Treg limit intestinal pathology during nematode infection and that they control the onset and magnitude of the anti-parasitic Th Th2 response. Using mice expressing the diphtheria toxin receptor under the control of the foxp3 locus, we removed Foxp3(+) Treg during the early phase of infection with Heligmosomoides polygyrus bakeri. Depletion of Treg in infected animals did not affect adult worm burden, but led to increased pathology at the site of infection. Infected, depleted mice displayed higher frequencies of activated CD4(+) T cells and increased levels of the Th2 cytokines IL-4 and IL-13. The stronger parasite-specific Th2 response was accompanied by higher levels of IL-10. Only a moderate change in Th1 (IFN-gamma) reactivity was detected in worm-infected, Treg-depleted mice. Furthermore, we detected an accelerated onset of parasite-specific Th2 and IL-10 responses in the transient absence of Foxp3(+) Treg. However, adult worm burdens were not affected by the increased Th2-reactivity in Treg-depleted mice. Hence, our data show that Treg restrict the onset and strength of Th2 responses during intestinal worm infection, while increasing primary Th2 responses does not necessarily lead to killing of larvae or accelerated expulsion of adult worms.

Trichuris suis ova therapy for allergic rhinitis: a randomized, double-blind, placebo-controlled clinical trial

BACKGROUND

Parasitic helminth infections can protect against allergic airway inflammation in experimental models and have been associated with a reduced risk of atopy and a reduced course of asthma in some observational studies. Although no clinical evidence exists to support the use of helminth therapy for allergic disease, the helminth Trichuris suis has demonstrated efficacy in treatment of inflammatory bowel disease.

OBJECTIVE

To determine efficacy of helminth therapy for allergic rhinitis.

METHODS

We conducted a double-blind, placebo-controlled, parallel group trial in which 100 subjects age 18 to 65 years with grass pollen-induced allergic rhinitis were randomly assigned to ingest a total of 8 doses with 2500 live T suis ova or placebo with an interval of 21 days. The primary outcome was a change in mean daily total symptom score for runny, itchy, sneezing nose (maximum change, 9.0) or in percentage of well days during the grass pollen season.

RESULTS

Treatment with T suis ova (N = 49) compared with placebo (N = 47) caused transient diarrhea peaking at day 41 in 33% of participants (placebo, 2%), and increased eosinophil counts (P < .001) and T suis-specific IgE (P < .05), IgG (P < .001), IgG(4) (P < .003), and IgA (P < .001), whereas there was no significant change in symptom scores (0.0; 95% CI, -0.5 to 0.4; P = .87), well days (3%; 95% CI, -9% to 14%; P = .63), total histamine (P = .44), grass-specific IgE (P = .76), or diameter of wheal reaction on skin prick testing with grass (P = .85) or 9 other allergens.

CONCLUSION

Repeated treatment with the helminth T suis induced a substantial clinical and immunologic response as evidence of infection, but had no therapeutic effect on allergic rhinitis.