Host Defense Versus Immunosuppression: Unisexual Infection With Male or Female Schistosoma mansoni Differentially Impacts the Immune Response Against Invading Cercariae

Schistosoma excretory/secretory products: an untapped library of tolerogenic immunotherapeutics against food allergy

Food allergy (FA) is considered the 'second wave' of the allergy epidemic in developed countries after asthma and allergic rhinitis with a steadily growing burden of 40%. The absence of early childhood pathogen stimulation embodied by the hygiene hypothesis is one explanation, and in particular, the eradication of parasitic helminths could be at play. Infections with parasites Schistosoma spp. have been found to have a negative correlation with allergic diseases. Schistosomes induce regulatory responses to evade immune detection and ensure their long-term survival. This is achieved via excretory/secretory (E/S) products, consisting of proteins, lipids, metabolites, nucleic acids and extracellular vesicles, representing an untapped therapeutic avenue for the treatment of FA without the unpleasant side-effects and risks associated with live infection. Schistosome-derived immunotherapeutic development is in its infancy and novel discoveries are heavily technology dependent; thus, it is essential to better understand how newly identified molecules interact with host immune systems to ensure safety and successful translation. This review will outline the identified Schistosoma-derived E/S products at all life cycle stages and discuss known mechanisms of action and their ability to suppress FA.

Utilization of a highly adaptable murine air pouch model for minimally invasive testing of the inflammatory potential of biomaterials

Introduction: The biocompatibility of an implanted material strongly determines the subsequent host immune response. After insertion into the body, each medical device causes tissue reactions. How intense and long-lasting these are is defined by the material properties. The so-called foreign body reaction is a reaction leading to the inflammation and wound healing process after implantation. The constantly expanding field of implant technology and the growing areas of application make optimization and adaptation of the materials used inevitable. Methods: In this study, modified liquid silicone rubber (LSR) and two of the most commonly used thermoplastic polyurethanes (TPU) were compared in terms of induced inflammatory response in the body. We evaluated the production of inflammatory cytokines, infiltration of inflammatory cells and encapsulation of foreign bodies in a subcutaneous air-pouch model in mice. In this model, the material is applied in a minimally invasive procedure via a cannula and in one piece, which allows material testing without destroying or crushing the material and thus studying an intact implant surface. The study design includes short-term (6 h) and long-term (10 days) analysis of the host response to the implanted materials. Air-pouch-infiltrating cells were determined by flow cytometry after 6 h and 10 days. Inflammation, fibrosis and angiogenesis markers were analyzed in the capsular tissue by qPCR after 10 days. Results: The foreign body reaction was investigated by macroscopic evaluation and scanning electron microscopy (SEM). Increased leukocyte infiltration was observed in the air-pouch after 6 h, but it markedly diminished after 10 days. After 10 days, capsule formations were observed around the materials without visible inflammatory cells. Discussion: For biocompatibility testing materials are often implanted in muscle tissue. These test methods are not sufficiently conclusive, especially for materials that are intended to come into contact with blood. Our study primarily shows that the presented model is a highly adaptable and minimally invasive test system to test the inflammatory potential of and foreign body reaction to candidate materials and offers more precise analysis options by means of flow cytometry.

Individually or as a Team-The Immunological Milieu in the Lung Caused by Migrating Single-Sex or Mixed-Sex Larvae of Schistosoma mansoni

While the lung is considered an efficient site for stopping the larvae of the acute Schistosoma spp. infection phase from migrating through extensive inflammatory responses in the surrounding tissues, little is known about these processes. To date, the highest resistance to infection has been achieved in experimental studies with radiation-attenuated cercariae immunization, which elicits a strong Th1/Th2 response in the lung and results in up to 80% protection. Based on our own studies demonstrating a systemic, unpolarized Th1/Th2 response resulting from infection with male or female Schistosoma mansoni, we hypothesize that this atypical immune response is already detectable during the pulmonary passage of parasite larvae. Therefore, we examined the immune milieu in the lungs of mice caused by migrating schistosome larvae, either male or female (single-sex groups) or male + female (bisexual control), 4 and 16 days after infection in bronchoalveolar lavage and lung tissue by flow cytometry, qPCR, and multiplex analyzes. Our results show only minor differences in the inflammatory profile between the single-sex groups but significant differences compared with the bisexual control group. Both single-sex infected groups have increased expression of inflammatory markers in lung tissue, higher numbers of cytotoxic T cells (day 4 post-infection) and more T helper cells (day 16 post-infection), compared with the bisexual control group. A single-sex infection, regardless of whether it is an infection with male or female cercariae, causes an immune milieu in the lung that is clearly different from an infection with both sexes. In terms of identifying therapeutic targets to achieve resistance to re-infection, it is of great scientific interest to identify the differences in the inflammatory potential of male or female and male + female parasites.

Safety and infectivity of female cercariae in Schistosoma-naïve, healthy participants: a controlled human Schistosoma mansoni infection study

BACKGROUND

A controlled human infection model for schistosomiasis (CHI-S) can speed up vaccine development and provides insight into early immune responses following schistosome exposure. Recently, we established CHI-S model using single-sex male-only Schistosoma mansoni (Sm) cercariae in Schistosoma-naïve individuals. Given important differences in antigenic profile and human immune responses to schistosomes of different sex, we pioneered a single-sex female-only CHI-S model for future use in vaccine development.

METHODS

We exposed 13 healthy, Schistosoma-naïve adult participants to 10 (n = 3) or 20 (n = 10) female cercariae and followed for 20 weeks, receiving treatment with praziquantel (PZQ) 60 mg/kg at week 8 and 12 after exposure.

FINDINGS

The majority (11/13) participants reported rash and/or itch at the site of exposure, 5/13 had transient symptoms of acute schistosomiasis. Exposure to 20 cercariae led to detectable infection, defined as serum circulating anodic antigen levels >1.0 pg/mL, in 6/10 participants. Despite two rounds of PZQ treatment, 4/13 participants showed signs of persistent infection. Additional one- or three-day PZQ treatment (1 × 60 mg/kg and 3 × 60 mg/kg) or artemether did not result in cure, but over time three participants self-cured. Antibody, cellular, and cytokine responses peaked at week 4 post infection, with a mixed Th1, Th2, and regulatory profile. Cellular responses were (most) discriminative for symptoms.

INTERPRETATION

Female-only infections exhibit similar clinical and immunological profiles as male-only infections but are more resistant to PZQ treatment. This limits future use of this model and may have important implications for disease control programs.

FUNDING

European Union's Horizon 2020 (grant no. 81564).

Unisexual infection with Schistosoma mansoni in mice has the potential to boost the immune response against eggs after challenge infection

Introduction

The complexity of the Schistosoma spp. life cycle and their effective immune evasion strategies, makes vaccine development challenging. Unisexual infection models, that excludes any immunomodulatory effects of the parasite eggs, may contribute to a better understanding of complex immunological processes and identification of new targets for vaccine research. We have recently shown that long-term unisexual infection with schistosomes in mice results in an unpolarized Th1/Th2 response associated with an abnormally enlarged spleen and diffuse liver inflammation. Herein, we investigated whether (i) unisexual worms can mate after three months of single sex infection and (ii) thus the Th2 response induced by oviposition can reverse or heal the described systemic inflammation.

Methods

Therefore, we infected 6-8 weeks old female C57BL/6j mice with 100 male or female cercariae and reinfected with the opposite sex for the same period after 12 weeks. At 24 weeks after initial infection, we histologically examined worm mating, as evidenced by the presence of parasite eggs, infection-related pathology associated with eggs, and characterization of fibrosis in the livers.

Results

Single worms are able to mate months after unisexual infection and start oviposition. Egg deposition has been associated with a typical Th2 immune response in the liver after unisexual reinfection, accompanied by increased recruitment of CD4+ T cells. Hepatic collagen levels were significantly increased in the reinfected groups compared to the naive and unisexually infected group.

Discussion

Our results indicate that the eggs are able to restore the Th1/Th2 immune balance of a previous unisexual infection. However, the organ damage caused by the unisexual worms does not subside, but rather provides the baseline for the emerging egg-triggered inflammation and fibrosis. Since single schistosomes can mate even several weeks after unisexual infection and then accumulate worm- and egg-related organ damage, infection status without positive egg detection is very important, especially in areas with low prevalence.

Single-sex schistosomiasis: a mini review

Schistosomiasis is a neglected tropical disease caused by dioecious blood flukes of the genus Schistosoma and second to malaria as a parasitic disease with significant socio-economic impacts. Mating is essential for maturation of male and female schistosomes and for females to lay of eggs, which are responsible for the pathogenesis and propagation of the life cycle beyond the mammalian host. Single-sex schistosomes, which do not produce viable eggs without mating, have been overlooked given the symptomatic paucity of the single-sex schistosomiasis and limited diagnostic toolkit. Besides, single-sex schistosomes are less sensitive to praziquantel. Therefore, these issues should be considered to achieve the elimination of this infection disease. The aim of this review is to summarize current progress in research of single-sex schistosomes and host-parasite interactions.

A one-year unisexual Schistosoma mansoni infection causes pathologic organ alterations and persistent non-polarized T cell-mediated inflammation in mice

In exhibiting gonochorism and phenotypic sexual dimorphism, Schistosoma spp. are unique among trematodes. Only females mating with male schistosomes can produce the highly immunogenic parasite eggs which determine the clinical picture of the disease schistosomiasis. The strong immune-modulatory effect of the eggs masks the influence of the adult worms. To shed light on the complexity of the immune response triggered by adult worms of Schistosoma mansoni, we performed a long-term unisexual infection experiment in mice. We were able to demonstrate that both male and female schistosomes can survive unpaired for one year in the murine host. Furthermore, unisexual S. mansoni infection leads to pronounced inflammation of the liver characterized by a non-polarized Th1/Th2 immune response, regardless of worm sex.

Pattern recognition receptor signaling and innate immune responses to schistosome infection

Schistosomiasis remains to be a significant public health problem in tropical and subtropical regions. Despite remarkable progress that has been made in the control of the disease over the past decades, its elimination remains a daunting challenge in many countries. This disease is an inflammatory response-driven, and the positive outcome after infection depends on the regulation of immune responses that efficiently clear worms and allow protective immunity to develop. The innate immune responses play a critical role in host defense against schistosome infection and pathogenesis. Initial pro-inflammatory responses are essential for clearing invading parasites by promoting appropriate cell-mediated and humoral immunity. However, elevated and prolonged inflammatory responses against the eggs trapped in the host tissues contribute to disease progression. A better understanding of the molecular mechanisms of innate immune responses is important for developing effective therapies and vaccines. Here, we update the recent advances in the definitive host innate immune response to schistosome infection, especially highlighting the critical roles of pattern recognition receptors and cytokines. The considerations for further research are also provided.

Sex-Specific Modulation of the Host Transcriptome in the Spleen of Schistosoma mansoni-Infected Mice

Background

Schistosomiasis is a severe parasitic disease that is primarily driven by the host’s immune response to schistosome eggs trapped in tissue and by the granulomatous inflammatory and fibrotic reaction they cause. Despite significant progress in understanding the complex immunological processes involved in the relationship between schistosomes and their host, neither an effective vaccine against the infection nor anti-fibrotic drugs currently exists, making the search for new targets for schistosome drugs and vaccine candidates even more important. In order to identify new molecular targets for defense against or elimination of the parasite, we investigate herein the interplay between the host and male or female schistosomes, clearly separating this from the action of the parasite eggs.

Methods

For this purpose, we infected 6–8-week-old female NMRI mice with 100 male (M), female (F), or both (MF) S. mansoni cercariae and performed a comparative transcriptomic and flow cytometric analysis of their spleens.

Results

Principal component analysis of a total of 22,207 transcripts showed a clear clustering of the experimental groups. We identified a total of 1,293 genes in group M, 512 genes in group F, and 4,062 genes in group MF that were differentially expressed compared to naive controls. The highest percentage of regulated genes (2,972; 65.9%) was found in group MF alone, but there was a large overlap between groups M and MF (798; 17.7%) and a small overlap between groups F and MF (91; 2.0%). Only 4.5% of genes (201) were revealed to be regulated in all experimental groups (M/F/MF). In addition, we were able to show that both worm sexes trigger immune responses in an egg-independent manner (non-polarized Th1 and Th2 response), with female worms exerting less regulatory influence than males.

Conclusion

Our data show that adult schistosomes trigger sex-specific, egg-independent immune responses. The lists of genes regulated by adult female or male worms presented here may be useful in deciphering host–parasite interactions to identify targets for schistosome elimination.

Comparative proteome analysis of the tegument of male and female adult Schistosoma mansoni

The tegument, as the surface layer of adult male and female Schistosoma spp. represents the protective barrier of the worms to the hostile environment of the host bloodstream. Here we present the first comparative analysis of sex-specific tegument proteins of paired or virgin Schistosoma mansoni. We applied a new and highly sensitive workflow, allowing detection of even low abundance proteins. Therefore, a streptavidin–biotin affinity purification technique in combination with single pot solid-phase enhanced sample preparation was established for subsequent LC–MS/MS analysis. We were able to identify 1519 tegument proteins for male and female virgin and paired worms and categorized them by sex. Bioinformatic analysis revealed an involvement of female-specific tegument proteins in signaling pathways of cellular processes and antioxidant mechanisms. Male-specific proteins were found to be enriched in processes linked to phosphorylation and signal transduction. This suggests a task sharing between the sexes that might be necessary for survival in the host. Our datasets provide a basis for further studies to understand and ultimately decipher the strategies of the two worm sexes to evade the immune system.

Previous History of American Tegumentary Leishmaniasis Alters Susceptibility and Immune Response Against Schistosoma mansoni Infection in Humans

Schistosomiasis and Leishmaniasis are chronic parasitic diseases with high prevalence in some tropical regions and, due to their wide distribution, a risk of co-infections is present in some areas. Nevertheless, the impact of this interaction on human populations is still poorly understood. Thus, the current study evaluated the effect of previous American Tegumentary Leishmaniasis (ATL) on the susceptibility and immune response to Schistosoma mansoni infection in residents from a rural community in Northern of Minas Gerais state, Brazil, an area endemic for both parasitic infections. The participants answered a socioeconomic questionnaire and provided stool and blood samples for parasitological and immunological evaluations. Stool samples were examined by a combination of parasitological techniques to identify helminth infections, especially S. mansoni eggs. Blood samples were used for hemograms and to measure the serum levels of cytokines and chemokines. Reports on previous ATL were obtained through interviews, clinical evaluation forms, and medical records. S. mansoni infection was the most prevalent parasitic infection in the study population (46%), and the majority of the infected individuals had a very low parasite burden. In the same population, 93 individuals (36.2%) reported previous ATL, and the prevalence of S. mansoni infection among these individuals was significantly higher than among individuals with no ATL history. A multiple logistic regression model revealed that S. mansoni infection was positively associated with higher levels of CCL3 and CCL17, and a higher frequency of IL-17 responders. Moreover, this model demonstrated that individuals with an ATL history had a 2-fold higher probability to be infected with S. mansoni (OR = 2.0; 95% CI 1.04–3.68). Among S. mansoni-infected individuals, the logistic regression demonstrated that a previous ATL history was negatively associated with the frequency of IL-17 responders and CXCL10 higher responders, but positively associated with higher IL-27 responders. Altogether, our data suggest that previous ATL may alter the susceptibility and the immune response in S. mansoni-infected individuals, which may likely affect the outcome of schistosomiasis and the severity of the disease in humans.

Monosexual Cercariae of Schistosoma japonicum Infection Protects Against DSS-Induced Colitis by Shifting the Th1/Th2 Balance and Modulating the Gut Microbiota

Inflammatory bowel disease (IBD)-related inflammation is closely associated with the initiation and progression of colorectal cancer. IBD is generally treated with 5-aminosalicylic acid and immune-modulating medication, but side effects and limitations of these therapies are emerging. Thus, the development of novel preventative or therapeutic approaches is imperative. Here, we constructed a dextran sodium sulphate (DSS)-induced IBD mouse model that was infected with monosexual Schistosoma japonicum cercariae (mSjci) at day 1 or administered dexamethasone (DXM) from days 3 to 5 as a positive control. The protective effect of mSjci on IBD mice was evaluated through their assessments of their clinical signs, histopathological lesions and intestinal permeability. To uncover the underlying mechanism, the Th1/Th2 balance and Treg cell population were also examined. Additionally, the alterations in the gut microbiota were assessed to investigate the interaction between the mSjci-modulated immune response and pathogenic microbiome. Mice treated with DSS and mSjci showed fewer IBD clinical signs and less impaired intestinal permeability than DSS-treated mice. Mechanistically, mSjci modulated the Th1/Th2 balance by repressing IFN-γ production, promoting IL-10 expression and enhancing the Treg subset population. Moreover, mSjci notably reshaped the structure, diversity and richness of the gut microbiota community and subsequently exerted immune-modulating effects. Our findings provide evidence showing that mSjci might serve as a novel and effective protective strategy and that the gut microbiota might be a new therapeutic target in IBD.

Duplex real-time PCR for sexing Schistosoma japonicum cercariae based on W chromosome-specific genes and its applications

As a unique feature among otherwise hermaphroditic trematodes, Schistosoma species are gonochoric parasites whose sex is genetically determined (ZZ for males and ZW for females). However, schistosome larvae are morphologically identical, and sex can only be discriminated by molecular methods. Here, we integrated published Schistosoma. japonicum transcriptome and genome data to identify W chromosome-specific genes as sex biomarkers. Three W chromosome-specific genes of S. japonicum were identified as sex biomarkers from a panel of 12 genes expressed only in females. An efficient duplex real-time PCR (qPCR) method for sexing cercariae was developed which could identify the sex of cercariae within 2 h without DNA extraction. Moreover, this method can be used to identify not only single-sex but also mixed-sex schistosome-infected snails. We observed a nearly equal proportion of single-male, single-female, and mixed-sex schistosome infections in artificially infected snails. Sex-known schistosome-infected snail models can be efficiently constructed with the aid of duplex qPCR. A field study revealed that single-sex schistosome infections were predominant among naturally infected snails. Finally, a schistosomiasis mouse model based on sex-known cercariae infection was shown to be more reliable than a model based on sex-unknown cercariae infection. The developed duplex qPCR method for sexing S. japonicum cercariae can be widely used for schistosomiasis modeling, genetic experiments, and field-based molecular epidemiological studies.

Schistosoma japonicum is a major causative agent of human schistosomiasis. Unlike other parasitic worms, S. japonicum females are determined by the heterogametic sex chromosome (ZW) and males by the homogametic sex chromosome (ZZ). The life cycle of S. japonicum includes the egg, miracidium, mother sporocyst, daughter sporocyst, cercaria, schistosomulum, and adult stages. The sex of adult male and female worms can be morphologically distinguished, whereas the sex of larvae, such as cercariae, can only be discriminated by molecular methods. In this study, we established an efficient duplex real-time PCR method for sexing S. japonicum cercariae based on newly identified W chromosome-specific genes. The established duplex real-time PCR method will facilitate construction of sex-controlled schistosome-infected intermediate host or definitive host models for schistosome-host interplays and schistosomiasis studies. This method is also a powerful tool for investigating the epidemiology of single-sex and mixed-sex schistosome-infected snails in the field.

Clinical Use of Schistosoma mansoni Antigens as Novel Immunotherapies for Autoimmune Disorders

The hygiene hypothesis states that improved hygiene and the resulting disappearance of once endemic diseases is at the origin of the enormous increase in immune related disorders such as autoimmune diseases seen in the industrialized world. Helminths, such as Schistosoma mansoni, are thought to provide protection against the development of autoimmune diseases by regulating the host's immune response. This modulation primarily involves induction of regulatory immune responses, such as generation of tolerogenic dendritic cells and alternatively activated macrophages. This points toward the potential of employing helminths or their products/metabolites as therapeutics for autoimmune diseases that are characterized by an excessive inflammatory state, such as multiple sclerosis (MS), type I diabetes (T1D) and inflammatory bowel disease (IBD). In this review, we examine the known mechanisms of immune modulation by S. mansoni, explore preclinical and clinical studies that investigated the use of an array helminthic products in these diseases, and propose that helminthic therapy opens opportunities in the treatment of chronic inflammatory disorders.

The peripheral immune response of mice infected with a neuropathogenic schistosome

Trichobilharzia regenti (Schistosomatidae) percutaneously infects birds and mammals and invades their central nervous system (CNS). Here, we characterized the peripheral immune response of infected mice and showed how it was influenced by the parasite-induced inflammation in the skin and the CNS. As revealed by flow cytometry, T cells expanded in the spleen and the CNS-draining lymph nodes 7-14 days post-infection. Both T-bet+ and GATA-3+ T cells were markedly elevated suggesting a mixed type 1/2 immune response. However, it dropped after 7 dpi most likely being unaffected by the neuroinflammation. Splenocytes from infected mice produced a high amount of IFN-γ and, to a lesser extent, IL-10, IL-4 and IL-17 after in vitro stimulation by cercarial homogenate. Nevertheless, it had only a limited capacity to alter the maturation status of bone marrow-derived dendritic cells (BMDCs), contrary to the recombinant T. regenti cathepsin B2, which also strongly augmented expression of Ccl5, Cxcl10, Il12a, Il33 and Il10 by BMDCs. Taken together, mice infected with T. regenti developed the mixed type 1/2 immune response, which was driven by the early skin inflammation rather than the late neuroinflammation. Parasite peptidases might play an active role in triggering the host immune response.

A controlled human Schistosoma mansoni infection model to advance novel drugs, vaccines and diagnostics

Schistosomiasis treatment relies on the use of a single drug, praziquantel, which is insufficient to control transmission in highly endemic areas¹. Novel medicines and vaccines are urgently needed^2,3. An experimental human model for schistosomiasis could accelerate the development of these products. We performed a dose-escalating clinical safety trial in 17 volunteers with male Schistosoma mansoni cercariae, which do not produce eggs (clinicaltrials.gov NCT02755324), at the Leiden University Medical Center, the Netherlands. The primary endpoints were adverse events and infectivity. We found a dose-related increase in adverse events related to acute schistosomiasis syndrome, which occurred in 9 of 17 volunteers. Overall, 5 volunteers (all 3 of the high dose group and 2 of 11 of the medium dose group) reported severe adverse events. Worm-derived circulating anodic antigen, the biomarker of the primary infection endpoint, peaked in 82% of volunteers at 3-10 weeks following exposure. All volunteers showed IgM and IgG1 seroconversion and worm-specific cytokine production by CD4⁺ T cells. All volunteers were cured with praziquantel provided at 12 weeks after exposure. Infection with 20 Schistosoma mansoni cercariae led to severe adverse events in 18% of volunteers and high infection rates. This infection model paves the way for fast-track product development for treatment and prevention of schistosomiasis.

Schistosoma mansoni Worm Infection Regulates the Intestinal Microbiota and Susceptibility to Colitis

Infection with parasite helminths induces potent modulation of the immune system of the host. Epidemiological and animal studies have shown that helminth infections can suppress or exacerbate unrelated autoimmune, allergic, and other inflammatory disorders. There is growing evidence that helminth infection-mediated suppression of bystander inflammatory responses is influenced by alterations in the intestinal microbiome modulating metabolic and immune functions of the infected host. We analyzed the fecal microbiota of mice infected with adult male Schistosoma mansoni worms, which are less susceptible to experimental colitis, and male- and female-worm-infected mice, which are highly sensitive to colitis. While both groups of infected mice developed a disrupted microbiota, there were marked alterations in mice with male and female worm infections. Antibiotic-treated recipients that were cohoused with both types of S. mansoni worm-infected mice acquired a colitogenic microbiome, leading to increased susceptibility to experimental colitis. Following anthelmintic treatment to remove worms from worm-only-infected mice, the mice developed exacerbated colitis. This study provides evidence that adult male S. mansoni worm infection modulates the host's immune system and suppresses bystander colitis while limiting dysbiosis of the host's intestinal microbiome during infection.