Allergic diseases and helminth infections

Effects of Schistosoma haematobium infection and treatment on the systemic and mucosal immune phenotype, gene expression and microbiome: A systematic review

BACKGROUND

Urogenital schistosomiasis caused by Schistosoma haematobium affects approximately 110 million people globally, with the majority of cases in low- and middle-income countries. Schistosome infections have been shown to impact the host immune system, gene expression, and microbiome composition. Studies have demonstrated variations in pathology between schistosome subspecies. In the case of S. haematobium, infection has been associated with HIV acquisition and bladder cancer. However, the underlying pathophysiology has been understudied compared to other schistosome species. This systematic review comprehensively investigates and assimilates the effects of S. haematobium infection on systemic and local host mucosal immunity, cellular gene expression and microbiome.

METHODS

We conducted a systematic review assessing the reported effects of S. haematobium infections and anthelmintic treatment on the immune system, gene expression and microbiome in humans and animal models. This review followed PRISMA guidelines and was registered prospectively in PROSPERO (CRD42022372607). Randomized clinical trials, cohort, cross-sectional, case-control, experimental ex vivo, and animal studies were included. Two reviewers performed screening independently.

RESULTS

We screened 3,177 studies and included 94. S. haematobium was reported to lead to: (i) a mixed immune response with a predominant type 2 immune phenotype, increased T and B regulatory cells, and select pro-inflammatory cytokines; (ii) distinct molecular alterations that would compromise epithelial integrity, such as increased metalloproteinase expression, and promote immunological changes and cellular transformation, specifically upregulation of genes p53 and Bcl-2; and (iii) microbiome dysbiosis in the urinary, intestinal, and genital tracts.

CONCLUSION

S. haematobium induces distinct alterations in the host's immune system, molecular profile, and microbiome. This leads to a diverse range of inflammatory and anti-inflammatory responses and impaired integrity of the local mucosal epithelial barrier, elevating the risks of secondary infections. Further, S. haematobium promotes cellular transformation with oncogenic potential and disrupts the microbiome, further influencing the immune system and genetic makeup. Understanding the pathophysiology of these interactions can improve outcomes for the sequelae of this devastating parasitic infection.

Impact of parasitic infection with Ascaris lumbricoides on pulmonary function tests in asthmatic and non-asthmatic children

Background

There is strong evidence for a causal relationship between helminthes infection and allergic disease like asthma due to the similarity in the way they respond. This study aimed to investigate the effects of Ascaris infection on pulmonary function tests (PFTs) to reveal the relationship between ascariasis and asthma in children.

Patients and methods

This a randomized-control study conducted in Basrah City, Iraq, in which four groups of a total of 490 children were enrolled: Group1 included 120 normal children; Group 2 included 135 asthmatic children; Group 3 who were 150 Ascaris infected children and group G4 included 85 asthmatic and Ascaris infected. PFTs, IgE level, differential blood count and parasitic examination were done for all groups.

Results

Both group2 and 4, which included asthmatic children showed a significant decrease in PFT (P > 0.05),while the PFT of parasitic infected group was not affected. There were no significant changes in WBC, eosinophils and IgE between asthmatic and parasitic infected groups.

Conclusion

Ascaris infection could induce the inflammatory immune response in children, but couldn't cause a significant effect on pulmonary function tests in these children; The impairment in PFT was due to asthma disease and not correlated to ascariasis.

Allergen-Specific Treg Cells Upregulated by Lung-Stage S. japonicum Infection Alleviates Allergic Airway Inflammation

Schistosoma japonicum infection showed protective effects against allergic airway inflammation (AAI). However, controversial findings exist especially regarding the timing of the helminth infection and the underlying mechanisms. Most previous studies focused on understanding the preventive effect of S. japonicum infection on asthma (infection before allergen sensitization), whereas the protective effects of S. japonicum infection (allergen sensitization before infection) on asthma were rarely investigated. In this study, we investigated the protective effects of S. japonicum infection on AAI using a mouse model of OVA-induced asthma. To explore how the timing of S. japonicum infection influences its protective effect, the mice were percutaneously infected with cercaria of S. japonicum at either 1 day (infection at lung-stage during AAI) or 14 days before ovalbumin (OVA) challenge (infection at post–lung-stage during AAI). We found that lung-stage S. japonicum infection significantly ameliorated OVA-induced AAI, whereas post–lung-stage infection did not. Mechanistically, lung-stage S. japonicum infection significantly upregulated the frequency of regulatory T cells (Treg cells), especially OVA-specific Treg cells, in lung tissue, which negatively correlated with the level of OVA-specific immunoglobulin E (IgE). Depletion of Treg cells in vivo partially counteracted the protective effect of lung-stage S. japonicum infection on asthma. Furthermore, transcriptomic analysis of lung tissue showed that lung-stage S. japonicum infection during AAI shaped the microenvironment to favor Treg induction. In conclusion, our data showed that lung-stage S. japonicum infection could relieve OVA-induced asthma in a mouse model. The protective effect was mediated by the upregulated OVA-specific Treg cells, which suppressed IgE production. Our results may facilitate the discovery of a novel therapy for AAI.

Intestinal helminthic infection and allergic disorders among school children enrolled in mass deworming program, Sululta, Ethiopia

BACKGROUND

Intestinal helminths have been proposed to have a protective role against allergic sensitization and atopic diseases. However, consistent data demonstrating this are lacking in Sub-Saharan countries. We aimed to assess the association between intestinal helminths and allergic disorders among school children enrolled in mass deworming program in Sululta, Ethiopia.

METHODS

A cross sectional study was conducted among 526 school children aged 5 to 14 years old from primary government schools in Sululta district, Ethiopia. An interviewer-led questionnaire administered to parents provided information on demographic and lifestyle variables. Questions on allergic disease symptoms were collected using the International Study of Asthma and Allergies in Children (ISAAC) questionnaire 6 months following deworming treatments. Atopy was defined as a positive skin prick test reaction to one or both dust mite (Dermatophagoides) and German cockroach (Blatella germanica) allergens. Fresh stool samples were collected, processed, and examined by direct wet mount, Kato-Katz technique, and formol-ether concentration technique. Multivariate logistic regressions were used to assess the association between allergic disorder and helminths infection.

RESULTS

Of the total 526 school children, 58.2% were females. Overall, 24% (126/526) had allergic symptoms, 5.1% (27/526) had atopy, and 16.9% (89/526) had intestinal helminths. There was no association between helminthic infection and self-reported allergic symptoms (P = 0.317), but Ascaris lumbricoides infection was positively associated with atopy (AOR = 4.307, 95% CI 1.143-16.222, P = 0.031). Atopy was related to increased allergy symptoms (AOR = 2.787, 95% CI 1.253-6.197, P = 0.012), and family history of allergy was associated with increased childhood allergy (AOR = 2.753, 95% CI 1.565-4.841, P = 0.001). Deworming in the past 6 months showed a reduced odd of self-reported allergic symptoms (AOR = 0.581, 95% CI 0.366-0.954, P = 0.034).

CONCLUSION

While no significant association between self-reported allergy and helminths was found in this study, this may have been due to the low prevalence and intensity of helminthic infection in the sample. There was a positive association between Ascaris lumbricoides and atopy. To further examine the underlying mechanism behind this positive association, a longitudinal study is needed.

Inflammaging in Endemic Areas for Infectious Diseases

Immunosenescence is marked by a systemic process named inflammaging along with a series of defects in the immunological activity that results in poor responses to infectious agents and to vaccination. Inflammaging, a state of low-grade chronic inflammation, usually leads to chronic inflammatory diseases and frailty in the elderly. However, some elderly escape from frailty and reach advanced age free of the consequences of inflammaging. This process has been called immunological remodeling, and it is the hallmark of healthy aging as described in the studies of centenarians in Italy. The biological markers of healthy aging are still a matter of debate, and the studies on the topic have focused on inflammatory versus remodeling processes and molecules. The sub-clinical inflammatory status associated with aging might be a deleterious event for populations living in countries where chronic infectious diseases are not prevalent. Nevertheless, in other parts of the world where they are, two possibilities may occur. Inflammatory responses may have a protective effect against these infectious agents. At the same time, the long-term consequences of protective immune responses during chronic infections may result in accelerated immunosenescence in these individuals. Therefore, the biological markers of healthy aging can vary according to environmental, cultural, and geographical settings that reflect worldwide, and in a non-biased, non-westernized perspective, the changes that we experience regarding our contacts with microorganisms and the outcomes of such contacts.

Initiating pollen sensitization - complex source, complex mechanisms

The mechanisms involved in the induction of allergic sensitization by pollen are not fully understood. Within the last few decades, findings from epidemiological and experimental studies support the notion that allergic sensitization is not only dependent on the genetics of the host and environmental factors, but also on intrinsic features of the allergenic source itself. In this review, we summarize the current concepts and newest advances in research focusing on the initial mechanisms inducing pollen sensitization. Pollen allergens are embedded in a complex and heterogeneous matrix composed of a myriad of bioactive molecules that are co-delivered during the allergic sensitization. Surprisingly, several purified allergens were shown to lack inherent sensitizing potential. Thus, growing evidence supports an essential role of pollen-derived components co-delivered with the allergens in the initiation of allergic sensitization. The pollen matrix, which is composed by intrinsic molecules (e.g. proteins, metabolites, lipids, carbohydrates) and extrinsic compounds (e.g. viruses, particles from air pollutants, pollen-linked microbiome), provide a specific context for the allergen and has been proposed as a determinant of Th2 polarization. In addition, the involvement of various pattern recognition receptors (PRRs), secreted alarmins, innate immune cells, and the dependency of DCs in driving pollen-induced Th2 inflammatory processes suggest that allergic sensitization to pollen most likely results from particular combinations of pollen-specific signals rather than from a common determinant of allergenicity. The exact identification and characterization of such pollen-derived Th2-polarizing molecules should provide mechanistic insights into Th2 polarization and pave the way for novel preventive and therapeutic strategies against pollen allergies.

Helminths of urban rats in developed countries: a systematic review to identify research gaps

Although black (Rattus rattus) and brown (Rattus norvegicus) rats are among the most widespread synanthropic wild rodents, there is a surprising scarcity of knowledge about their ecology in the urban ecosystem. In particular, relatively few studies have investigated their helminth species diversity in such habitat. We followed the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analysis) guideline to synthesize the existing published literature regarding the helminth fauna of urban rats in developed countries (North America, Europe, Australia, New Zealand and Japan). We aimed at describing the species diversity and richness of urban rat helminths, the species prevalence and associations, the methods of investigation, the pathological changes observed in the hosts, the risk factors of infection and the public health significance of rat-borne helminthiases. Twenty-three scientific papers published between 1946 and 2019 were reviewed, half of them were conducted in Europe. Twenty-five helminth species and eight genera were described from the liver, digestive tract, lungs and muscles of urban rats. The most commonly reported parasite was Calodium hepaticum. Prevalence and risk factors of helminth infection in urban rats varied greatly between studies. Observed pathological findings in the rat host were generally minor, except for C. hepaticum. Several rat helminths can parasitize humans and are therefore of public health significance. The lack of references to identification keys and the rare use of molecular tools for species confirmation represent the main limitation of these studies. Knowledge gap on this topic and the needs for future research are discussed.

Exposure to Toxocara spp. and Ascaris lumbricoides infections and risk of allergic rhinitis in children

Background

Substantial experimental studies suggest a role for helminthes infections in the pathogenesis of allergies, but epidemiologic data have been inconsistent. Unlike to asthma, the association between helminthes infection and allergic rhinitis (AR) has been poorly studied. Therefore, we sought to evaluate the association between exposure to Ascaris and Toxocara infections and AR.

Methods

We did an age- and gender-matched case–control study of 81 children with physician-confirmed AR and 101 control subjects in a referral hospital for pediatric diseases in northern Iran. Exposure to Ascaris and Toxocara infections was evaluated by anti-A. lumbricoides- and anti-Toxocara- IgG antibodies using a commercial enzyme-linked immunosorbent assay. Associations were determined using multivariate logistic regression.

Results

Ascaris seropositivity was higher in children with rhinitis than in controls (12.34 vs. 3.96%). Ascaris seropositivity was positively associated with AR in univariate analysis (OR, 3.42; 95% CI 1.03–11.3; P value = 0.035), but this association was not significant after adjustment for potential confounders (OR, 1.85; 95% CI 0.42–8.18). Also Toxocara seropositivity was higher in children with AR than in healthy subjects (3.7% vs. 0.99), indicating non-significant association with AR in both univariate (OR, 3.84; 95% CI 0.39–37.7) and multivariate analyses (OR, 0.8; 95% CI 0.04–15.44).

Conclusion

Our results revealed that AR is not associated with seropositivity to Ascaris and Toxocara infections in general; however, a higher seropositivity rate was found for both parasites in children with AR. More studies with longitudinal design and larger sample size are needed to elucidate this association.

Allergen-Specific Immunotherapy With Liposome Containing CpG-ODN in Murine Model of Asthma Relies on MyD88 Signaling in Dendritic Cells

Changing the immune responses to allergens is the cornerstone of allergen immunotherapy. Allergen-specific immunotherapy that consists of repeated administration of increasing doses of allergen extract is potentially curative. The major inconveniences of allergen-specific immunotherapy include failure to modify immune responses, long-term treatment leading to non-compliance and the potential for developing life-threating anaphylaxis. Here we investigated the effect of a novel liposomal formulation carrying low dose of allergen combined with CpG-ODN, a synthetic TLR9 agonist, on established allergic lung inflammation. We found that challenge with allergen (OVA) encapsulated in cationic liposome induced significantly less severe cutaneous anaphylactic reaction. Notably, short-term treatment (three doses) with a liposomal formulation containing co-encapsulated allergen plus CpG-ODN, but not allergen or CpG-ODN alone, reversed an established allergic lung inflammation and provided long-term protection. This liposomal formulation was also effective against allergens derived from Blomia tropicalis mite extract. The attenuation of allergic inflammation was not associated with increased numbers of Foxp3-positive or IL-10-producing regulatory T cells or with increased levels of IFN-gamma in the lungs. Instead, the anti-allergic effect of the liposomal formulation was dependent of the innate immune signal transduction generated in CD11c-positive putative dendritic cells expressing MyD88 molecule. Therefore, we highlight the pivotal role of dendritic cells in mediating the attenuation of established allergic lung inflammation following immunotherapy with a liposomal formulation containing allergen plus CpG-ODN.

Human Toxocara Infection: Allergy and Immune Responses

BACKGROUND

Toxocariasis is a cosmopolitan infection that occurs in various regions worldwide, more frequently in developing countries. Chronic infections with Toxocara species in humans are associated with the production of high levels of specific and non-specific antibodies of all isotypes and IgG subclasses and a cytokine response characterized by the production of Th2 cytokines including IL-4, IL-5 and IL-13 by Peripheral Blood Monocytes (PBMCs) and Leukocytes (PBLs) in whole blood cultures. Other Th2 effector responses are also prominent during infection, reflected by elevated numbers of peripheral blood eosinophils and increased expression of eosinophil degranulation products. The production of IFN-γ by PBMCs/PBLs stimulated with Toxocara-secreted proteins is not prominent in toxocariasis but IL-10 production may be increased in infected individuals. The relationship between Toxocara species with allergic reactions was reported in the recent century. Experimental and epidemiological investigations revealed that toxocariasis with this parasite led to the development of allergic symptoms, such as asthma. However, the findings are conflicting since in other investigations no association between these two immunopathologies has been reported.

CONCLUSION

The present review endeavours to summarize the data on Toxocara species and findings from studies on the relationship of toxocariasis with symptoms and signs of allergy. Furthermore, the mechanisms of immune responses and the factors associated between allergy and Toxocara infection are discussed.

Parasitic (Helminthic) Infection While on Asthma Biologic Treatment: Not Everything Is What It Seems

Asthma is a chronic inflammatory disorder of the airway that is characterized by bronchial hyperresponsiveness and variable airflow limitation. Approximately 235 million people are affected by asthma worldwide and 5–10% are considered to be refractory to standard asthma treatment. These patients are known to have repeated exacerbations requiring multiple courses of systemic corticosteroids and as a result, are at risk for increased adverse effects (i.e., osteoporosis, infections). Several new medications known as biologic agents have been approved for the treatment of moderate-to-severe asthmatics. These biologic agents target essential parts of the cell-mediated allergic and to a lesser degree non-allergic immune response (IgE, IL-5, and IL-4/IL-13). They are gaining more favor in the treatment of moderate-to-severe asthma due to their efficacy and excellent safety profile. Despite the most common adverse events being minor, such as injection site reactions, upper respiratory infections, or headaches, these agents carry a small risk of more severe complications such as anaphylaxis and decreased defense against parasitic infections (PI). The incidence of PI compared with other rare adverse events is not well reported, and there are no consensus guidelines for risk prevention of PI in asthmatics undergoing evaluation for, or currently using, biologic therapy. Thus, this article sets out to review the incidence of reported PI and other rare adverse events among asthmatics using current FDA-approved biologic therapies. Secondly, we discuss the clinical implications for the importance of risk prevention of PI with the use of biologic therapies in asthmatics. Lastly, we share an educational handout to assist providers in informing their patients of behaviors that could potentially increase their risk of PI while being on a biologic agent.

Dendritic Cell-Mediated Th2 Immunity and Immune Disorders

Dendritic cells (DCs) are the professional antigen-presenting cells that recognize and present antigens to naïve T cells to induce antigen-specific adaptive immunity. Among the T-cell subsets, T helper type 2 (Th2) cells produce the humoral immune responses required for protection against helminthic disease by activating B cells. DCs induce a Th2 immune response at a certain immune environment. Basophil, eosinophil, mast cells, and type 2 innate lymphoid cells also induce Th2 immunity. However, in the case of DCs, controversy remains regarding which subsets of DCs induce Th2 immunity, which genes in DCs are directly or indirectly involved in inducing Th2 immunity, and the detailed mechanisms underlying induction, regulation, or maintenance of the DC-mediated Th2 immunity against allergic environments and parasite infection. A recent study has shown that a genetic defect in DCs causes an enhanced Th2 immunity leading to severe atopic dermatitis. We summarize the Th2 immune-inducing DC subsets, the genetic and environmental factors involved in DC-mediated Th2 immunity, and current therapeutic approaches for Th2-mediated immune disorders. This review is to provide an improved understanding of DC-mediated Th2 immunity and Th1/Th2 immune balancing, leading to control over their adverse consequences.

The hygiene hypothesis at a glance: Early exposures, immune mechanism and novel therapies

The hygiene hypothesis was proposed almost three decades ago. Nevertheless, its mechanism still remains with relevant controversies. Some studies defend that early exposures during childhood to microbes and parasites are key determinants to prevent allergies and autoimmune diseases; however, other studies demonstrated that these early exposures can even potentiate the clinical scenario of the diseases. Based on several studies covering the influences of microbiome, parasites, related theories and others, this review focuses on recent advances in the hygiene hypothesis field. In addition, the main immunological mechanisms underlying the hygiene hypothesis are also discussed. We also strongly encourage that researchers do not consider the hygiene hypothesis as a theory based strictly on hygiene habits, but a theory combining diverse influences, as illustrated in this review as the hygiene hypothesis net.

Parasites and allergy: Observations from Brazil

Brazil is a middle-income country undergoing the epidemiological transition. Effects of changes in daily life habits and access to clean water, sanitation and urban services on a growing urban population have contributed to a double burden of both infectious and noncommunicable chronic diseases. Studies have indicated that parasite infections may modulate the human immune system and influence the development of allergic conditions such as asthma. However, there is no consensus in the published literature on the effects of parasitic infections on allergy, perhaps as a consequence of factors determining the epidemiology of these infections that vary between populations such as age of first infection, duration and chronicity of infections, parasite burden and species, and host genetic susceptibility. In this review, we discuss the observations from Brazil concerning the relationship between parasite infections and allergy.

Prevalence of Atopy following Mass Drug Administration with Albendazole: A Study in School Children on Flores Island, Indonesia

BACKGROUND

In many rural areas of tropical countries such as Indonesia, the prevalence of soil-transmitted helminths (STH) infections remains high. At the same time, the burden of allergic disorders in such rural areas is reported to be low and inversely associated with helminth infections. To reduce the morbidity and transmission of helminth infections, the world health organization recommends preventive treatment of school children by providing mass drug administration (MDA) with albendazole. Here, we had an opportunity to evaluate the prevalence of skin reactivity to allergens before and after albendazole treatment to get an indication of the possible impact of MDA on allergic sensitization.

METHODS

A study was conducted among 150 school children living in an area endemic for STH infections. Before and 1 year after anthelminthic treatment with albendazole, stool samples were examined for the presence of STH eggs, skin prick tests (SPT) for cockroach and house dust mites were performed, blood eosinophilia was assessed, and total immunoglobulin E (IgE) and C-reactive protein (CRP) were measured in plasma.

RESULTS

Anthelminthic treatment significantly reduced the prevalence of STH from 19.6 before treatment to 6% after treatment (p < 0.001). Levels of total IgE (estimate: 0.30; 95% CI 0.22-0.42, p < 0.0001), CRP (estimate: 0.60; 95% CI 0.42-0.86, p = 0.006), and eosinophil counts (estimate: 0.70; 95% CI 0.61-0.80, p < 0.001) decreased significantly. The prevalence of SPT positivity increased from 18.7 to 32.7%. Multivariate analysis adjusted for confounding factors showed an increased risk of being SPT positive to any allergen (OR 3.04; 95% CI 1.338-6.919, p = 0.008).

CONCLUSIONS

This study indicates that 1 year of MDA with albendazole was associated with a reduced prevalence of STH infections. This study shows that the prevalence of allergic sensitization increases after 1 year of albendazole treatment. Placebo-controlled and larger studies are needed to further substantiate a role of deworming treatment in an increased risk of allergic sensitization.