Cysteine protease inhibitor of Schistosoma japonicum - A parasite-derived negative immunoregulatory factor

Helminth-derived biomacromolecules as therapeutic agents for treating inflammatory and infectious diseases: What lessons do we get from recent findings?

Despite the tremendous progress in healthcare sectors, a number of life-threatening infectious, inflammatory, and autoimmune diseases are continuously challenging mankind throughout the globe. In this context, recent successes in utilizing helminth parasite-derived bioactive macromolecules viz. glycoproteins, enzymes, polysaccharides, lipids/lipoproteins, nucleic acids/nucleotides, and small organic molecules for treating various disorders primarily resulted from inflammation. Among the several parasites that infect humans, helminths (cestodes, nematodes, and trematodes) are known as efficient immune manipulators owing to their explicit ability to modulate and modify the innate and adaptive immune responses of humans. These molecules selectively bind to immune receptors on innate and adaptive immune cells and trigger multiple signaling pathways to elicit anti-inflammatory cytokines, expansion of alternatively activated macrophages, T-helper 2, and immunoregulatory T regulatory cell types to induce an anti-inflammatory milieu. Reduction of pro-inflammatory responses and repair of tissue damage by these anti-inflammatory mediators have been exploited for treating a number of autoimmune, allergic, and metabolic diseases. Herein, the potential and promises of different helminths/helminth-derived products as therapeutic agents in ameliorating immunopathology of different human diseases and their mechanistic insights of function at cell and molecular level alongside the molecular signaling cross-talks have been reviewed by incorporating up-to-date findings achieved in the field.

Immunological mechanisms involved in macrophage activation and polarization in schistosomiasis

Human schistosomiasis is caused by helminths of the genus Schistosoma. Macrophages play a crucial role in the immune regulation of this disease. These cells acquire different phenotypes depending on the type of stimulus they receive. M1 macrophages can be ‘classically activated’ and can display a proinflammatory phenotype. M2 or ‘alternatively activated’ macrophages are considered anti-inflammatory cells. Despite the relevance of macrophages in controlling infections, the role of the functional types of these cells in schistosomiasis is unclear. This review highlights different molecules and/or macrophage activation and polarization pathways during Schistosoma mansoni and Schistosoma japonicum infection. This review is based on original and review articles obtained through searches in major databases, including Scopus, Google Scholar, ACS, PubMed, Wiley, Scielo, Web of Science, LILACS and ScienceDirect. Our findings emphasize the importance of S. mansoni and S. japonicum antigens in macrophage polarization, as they exert immunomodulatory effects in different stages of the disease and are therefore important as therapeutic targets for schistosomiasis and in vaccine development. A combination of different antigens can provide greater protection, as it possibly stimulates an adequate immune response for an M1 or M2 profile and leads to host resistance; however, this warrants in vitro and in vivo studies.

Schistosome secretomes

Schistosomes are intravascular parasitic platyhelminths (blood flukes) that infect over 200 million people globally. Biomolecules secreted by the worms likely contribute to their ability to survive in the bloodstreams of immunocompetent hosts for many years. Here we review what is known about the protein composition of material released by the worms. Prominent among cercarial excretions/secretions (ES) is a ∼ 30 kDa serine protease called cercarial elastase (SmCE in Schistosoma mansoni), likely important in host invasion. Also prominent is a 117 amino acid non-glycosylated polypeptide (Sm16) that can impact several host cell-types to impinge on immunological outcomes. Similarly, components of the egg secretome (notably the 134 amino acid homodimeric glycoprotein "IL-4 inducing principle of schistosome eggs", IPSE, and the 225-amino acid monomeric T2 ribonuclease - omega-1) are capable of driving Th2-biased immune responses. A ∼36kDa chemokine binding glycoprotein SmCKBP, secreted by eggs, can negate the impact of several cytokines and can impede neutrophil migration. Of special interest is a disparate collection of classically cytosolic proteins that are surprisingly often identified in schistosome ES across life stages. These proteins, perhaps released as components of extracellular vesicles (EVs), include glycolytic enzymes, redox proteins, proteases and protease inhibitors, heat shock proteins, proteins involved in translation/turnover, histones, and others. Some such proteins may display "moonlighting" functions and, for example, impede blood clot formation around the worms. More prosaically, since several are particularly abundant soluble proteins, their appearance in the ES fraction may be indicative of worm damage ex vivo leading to protein leakage. Some bioactive schistosome ES proteins are in development as novel therapeutics against autoimmune, inflammatory, and other, non-parasitic, diseases.

A new ferritin SjFer0 affecting the growth and development of Schistosoma japonicum

Background

Schistosomiasis, an acute and chronic parasitic disease, causes substantial morbidity and mortality in tropical and subtropical regions of the world. Iron is an essential constituent of numerous macromolecules involving in important cellular reactions in virtually all organisms. Trematodes of the genus Schistosoma live in iron-rich blood, feed on red blood cells and store abundant iron in vitelline cells. Ferritins are multi-meric proteins that store iron inside cells. Three ferritin isoforms in Schistosoma japonicum are known, namely SjFer0, SjFer1 and SjFer2; however, their impact on the growth and development of the parasites  is still unknown. In this study we report on and characterize the ferritins in S. japonicum.

Methods

A phylogenetic tree of the SjFer0, SjFer1 and SjFer2 genes was constructed to show the evolutionary relationship among species of genus Schistosoma. RNA interference in vivo was used to investigate the impact of SjFer0 on schistosome growth and development.  Immunofluorescence assay was applied  to localize the expression of the ferritins. RNA-sequencing was performed  to characterize the iron transport profile after RNA interference.

Results

SjFer0 was found to have low similarity with SjFer1 and SjFer2 and contain an additional signal peptide sequence. Phylogenetic analysis revealed that SjFer0 can only cluster with some ferritins of other trematodes and tapeworms, suggesting that this ferritin branch might be unique to these parasites. RNA interference in vivo showed that SjFer0 significantly affected the growth and development of schistosomula but did not affect egg production of adult female worms. SjFer1 and SjFer2 had no significant impact on growth and development. The immunofluorescence study showed that SjFer0 was widely expressed in the somatic cells and vitelline glands but not in the testicle or ovary. RNA-sequencing indicated  that, in female, the ion transport process and calcium ion binding function were downregulated after SjFer0 RNA interference. Among the differentially downregulated genes, Sj-cpi-2, annexin and insulin-like growth factor-binding protein may be accounted for the suppression of schistosome growth and development.

Conclusions

The results indicate that SjFer0 affects the growth and development of schistosomula but does not affect egg production of adult female worms. SjFer0 can rescue the growth of the fet3fet4 double mutant Saccharomyces cerevisiae (strain DEY1453), suggesting being able to promote iron absorption. The RNA interference of SjFer0 inferred that  the suppression of worm growth and development may via  down-regulating Sj-cpi-2, annexin, and IGFBP.

Graphic Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-022-05247-1.

Molecular Characteristics and Potent Immunomodulatory Activity of Fasciola hepatica Cystatin

Cystatin, a cysteine protease inhibitor found in many parasites, plays important roles in immune evasion. This study analyzed the molecular characteristics of a cystatin from Fasciola hepatica (FhCystatin) and expressed recombinant FhCystatin (rFhcystatin) to investigate the immune modulatory effects on lipopolysaccharide-induced proliferation, migration, cytokine secretion, nitric oxide (NO) production, and apoptosis in mouse macrophages. The FhCystatin gene encoded 116 amino acids and contained a conserved cystatin-like domain. rFhCystatin significantly inhibited the activity of cathepsin B. rFhCystatin bound to the surface of mouse RAW264.7 cells, significantly inhibited cell proliferation and promoted apoptosis. Moreover, rFhCystatin inhibited the expression of cellular nitric oxide, interleukin-6, and tumor necrosis factor-α, and promoted the expression of transforming growth factor-β and interleukin-10. These results showed that FhCystatin played an important role in regulating the activity of mouse macrophages. Our findings provide new insights into mechanisms underlying the immune evasion and contribute to the exploration of potential targets for the development of new drug to control F. hepatica infection.

Regulatory effects of a novel cysteine protease inhibitor in Baylisascaris schroederi migratory larvae on mice immune cells

Background

The giant panda (Ailuropoda melanoleuca) is a well-known, rare and endangered species. Baylisascaris schroederi is a pathogenic ascarid. Infection with B. schroederi may cause death in giant pandas. At present, the immune evasion mechanism of B. schroederi is little known. Cysteine protease inhibitors (CPI) play important roles in the regulation of host immune responses against certain nematodes. In this study, we focused on the analysis of the regulation of B. schroederi migratory larvae CPI (rBsCPI-1) on mice immune cells.

Methods

First, the pattern recognition receptors on the surface of peripheral blood mononuclear cells (PBMCs) and the signal pathways that transduce extracellular signals into the nucleus activated by rBsCPI-1 were identified. Then, the regulatory effects of rBsCPI-1 on PBMCs physiological activities were detected. Finally, the effects of rBsCPI-1 on TLR signaling pathway activation and NF-κB phosphorylation in mice immunized with recombinant protein were analysed.

Results

The results suggested that rBsCPI-1 secreted by B. schroederi migratory larvae is mainly recognized by TLR2 and TLR4 on PBMCs. Extracellular signals are transduced into the nucleus through the MAPK and NF-κB signaling pathways, enhancing the phagocytosis, migration, and apoptosis of PBMCs; meanwhile, rBsCPI-1 induces high expression of NO. Thus, rBsCPI-1 plays a role in immune regulation. In addition, the high expression of negative regulatory factors also ensured that TLR activation is maintained at the optimal level.

Conclusions

rBsCPI-1 can transduce regulatory signals into immune cells by activating the TLR2/4-NF-κB/MAPK signaling pathway, having a certain regulatory effect on the physiological activities. Meanwhile, rBsCPI-1 can maintain the immune response in a balance by limiting the over-activation of the TLRs signaling pathway and thus contributes to B. schroederi immune evasion.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-022-05240-8.

Schistosome immunomodulators

Schistosomes are long lived, intravascular parasitic platyhelminths that infect >200 million people globally. The molecular mechanisms used by these blood flukes to dampen host immune responses are described in this review. Adult worms express a collection of host-interactive tegumental ectoenzymes that can cleave host signaling molecules such as the "alarmin" ATP (cleaved by SmATPDase1), the platelet activator ADP (SmATPDase1, SmNPP5), and can convert AMP into the anti-inflammatory mediator adenosine (SmAP). SmAP can additionally cleave the lipid immunomodulator sphingosine-1-phosphate and the proinflammatory anionic polymer, polyP. In addition, the worms release a barrage of proteins (e.g., SmCB1, SjHSP70, cyclophilin A) that can impinge on immune cell function. Parasite eggs also release their own immunoregulatory proteins (e.g., IPSE/α1, omega1, SmCKBP) as do invasive cercariae (e.g., Sm16, Sj16). Some schistosome glycans (e.g., LNFPIII, LNnT) and lipids (e.g., Lyso-PS, LPC), produced by several life stages, likewise affect immune cell responses. The parasites not only produce eicosanoids (e.g., PGE2, PGD2-that can be anti-inflammatory) but can also induce host cells to release these metabolites. Finally, the worms release extracellular vesicles (EVs) containing microRNAs, and these too have been shown to skew host cell metabolism. Thus, schistosomes employ an array of biomolecules-protein, lipid, glycan, nucleic acid, and more, to bend host biochemistry to their liking. Many of the listed molecules have been individually shown capable of inducing aspects of the polarized Th2 response seen following infection (with the generation of regulatory T cells (Tregs), regulatory B cells (Bregs) and anti-inflammatory, alternatively activated (M2) macrophages). Precisely how host cells integrate the impact of these myriad parasite products following natural infection is not known. Several of the schistosome immunomodulators described here are in development as novel therapeutics against autoimmune, inflammatory, and other, nonparasitic, diseases.

Therapeutic Effect of Schistosoma japonicum Cystatin on Atherosclerotic Renal Damage

Atherosclerosis is a chronic inflammation of the arterial vessel wall driven by lipid metabolism disorders. Although helminthic infection and their derivatives have been identified to attenuate the chronic inflammatory diseases, the immunomodulatory effect of recombinant Schistosoma japonicum cystatin (rSj-Cys) on metabolic diseases and atherosclerosis has not been reported. In this study, we investigated the therapeutic efficacy of rSj-Cys on atherosclerotic renal damage and explored the related immunological mechanism. The results demonstrated that treatment with rSj-Cys significantly reduced body weight gain, hyperlipidemia, and atherosclerosis induced by the high-fat diet in apoE^–/– mice. The treatment of rSj-Cys also significantly improved kidney functions through promoting macrophage polarization from M1 to M2, therefore inhibiting M1 macrophage–induced inflammation. The possible mechanism underlying the regulatory effect of rSj-Cys on reducing atherosclerosis and atherosclerotic renal damage is that rSj-Cys stimulates regulatory T cell and M2 macrophage polarization that produce regulatory cytokines, such as interleukin 10 and transforming growth factor β. The therapeutic effect of rSj-Cys on atherosclerotic renal damage is possibly through inhibiting the activation of TLR2/Myd88 signaling pathway. The results in this study provide evidence for the first time that Schistosoma-derived cystatin could be developed as a therapeutic agent to treat lipid metabolism disorder and atherosclerosis that threats million lives around the world.

Immunomics-Guided Antigen Discovery for Praziquantel-Induced Vaccination in Urogenital Human Schistosomiasis

Despite the enormous morbidity attributed to schistosomiasis, there is still no vaccine to combat the disease for the hundreds of millions of infected people. The anthelmintic drug, praziquantel, is the mainstay treatment option, although its molecular mechanism of action remains poorly defined. Praziquantel treatment damages the outermost surface of the parasite, the tegument, liberating surface antigens from dying worms that invoke a robust immune response which in some subjects results in immunologic resistance to reinfection. Herein we term this phenomenon Drug-Induced Vaccination (DIV). To identify the antigenic targets of DIV antibodies in urogenital schistosomiasis, we constructed a recombinant proteome array consisting of approximately 1,000 proteins informed by various secretome datasets including validated proteomes and bioinformatic predictions. Arrays were screened with sera from human subjects treated with praziquantel and shown 18 months later to be either reinfected (chronically infected subjects, CI) or resistant to reinfection (DIV). IgG responses to numerous antigens were significantly elevated in DIV compared to CI subjects, and indeed IgG responses to some antigens were completely undetectable in CI subjects but robustly recognized by DIV subjects. One antigen in particular, a cystatin cysteine protease inhibitor stood out as a unique target of DIV IgG, so recombinant cystatin was produced, and its vaccine efficacy assessed in a heterologous Schistosoma mansoni mouse challenge model. While there was no significant impact of vaccination with adjuvanted cystatin on adult worm numbers, highly significant reductions in liver egg burdens (45-55%, P<0.0001) and intestinal egg burdens (50-54%, P<0.0003) were achieved in mice vaccinated with cystatin in two independent trials. This study has revealed numerous antigens that are targets of DIV antibodies in urogenital schistosomiasis and offer promise as subunit vaccine targets for a drug-linked vaccination approach to controlling schistosomiasis.

Schistosoma japonicum Cystatin Alleviates Sepsis Through Activating Regulatory Macrophages

Multi-organ failure caused by the inflammatory cytokine storm induced by severe infection is the major cause of death for sepsis. Sj-Cys is a cysteine protease inhibitor secreted by Schistosoma japonicum with strong immunomodulatory functions on host immune system. Our previous studies have shown that treatment with Sj-Cys recombinant protein (rSj-Cys) attenuated inflammation caused by sepsis. However, the immunological mechanism underlying the immunomodulation of Sj-Cys for regulating inflammatory diseases is not yet known. In this study, we investigated the effect of Sj-Cys on the macrophage M2 polarization and subsequent therapeutic effect on sepsis. The rSj-Cys was expressed in yeast Pichia pastoris. Incubation of mouse bone marrow-derived macrophages (BMDMs) with yeast-expressed rSj-Cys significantly activated the polarization of macrophages to M2 subtype characterized by the expression of F4/80⁺ CD206⁺ with the elated secretion of IL-10 and TGF-β. Adoptive transfer of rSj-Cys treated BMDMs to mice with sepsis induced by cecal ligation and puncture (CLP) significantly improved their survival rates and the systemic clinical manifestations of sepsis compared with mice receiving non-treated normal BMDMs. The therapeutic effect of Sj-Cys-induced M2 macrophages on sepsis was also reflected by the reduced pathological damages in organs of heart, lung, liver and kidney and reduced serological levels of tissue damage-related ALT, AST, BUN and Cr, associated with downregulated pro-inflammatory cytokines (IFN-gamma and IL-6) and upregulated regulatory anti-inflammatory cytokines (IL-10 and TGF-β). Our results demonstrated that Sj-Cys is a strong immunomodulatory protein with anti-inflammatory features through activating M2 macrophage polarization. The findings of this study suggested that Sj-Cys itself or Sj-Cys-induced M2 macrophages could be used as therapeutic agents in the treatment of sepsis or other inflammatory diseases.

Immune Evasion Strategies of Schistosomes

Human schistosomes combat the unique immune systems of two vastly different hosts during their indirect life cycles. In gastropod molluscs, they face a potent innate immune response composed of variable immune recognition molecules and highly phagocytic hemocytes. In humans, a wide variety of innate and adaptive immune processes exist in proximity to these parasites throughout their lifespan. To survive and thrive as the second most common parasitic disease in humans, schistosomes have evolved many techniques to avoid and combat these targeted host responses. Among these techniques are molecular mimicry of host antigens, the utilization of an immune resistant outer tegument, the secretion of several potent proteases, and targeted release of specific immunomodulatory factors affecting immune cell functions. This review seeks to describe these key immune evasion mechanisms, among others, which schistosomes use to survive in both of their hosts. After diving into foundational observational studies of the processes mediating the establishment of schistosome infections, more recent transcriptomic and proteomic studies revealing crucial components of the host/parasite molecular interface are discussed. In order to combat this debilitating and lethal disease, a comprehensive understanding of schistosome immune evasion strategies is necessary for the development of novel therapeutics and treatment plans, necessitating the discussion of the numerous ways in which these parasitic flatworms overcome the immune responses of both hosts.

The Potential Role of Schistosome-Associated Factors as Therapeutic Modulators of the Immune System

The parasites and eggs of helminths, including schistosomes, are associated with factors that can modulate the nature and outcomes of host immune responses, particularly enhancing type 2 immunity and impairing the effects of type 1 and type 17 immunity. The main species of schistosomes that cause infection in humans are capable of generating a microenvironment that allows survival of the parasite by evasion of the immune response. Schistosome infections are associated with beneficial effects on chronic immune disorders, including allergies, autoimmune diseases, and alloimmune responses. Recently, there has been increasing research interest in the role of schistosomes in immunoregulation during human infection, and the mechanisms underlying these roles continue to be investigated. Further studies may identify potential opportunities to develop new treatments for immune disease. In this review, we provide an update on the advances in our understanding of schistosome-associated modulation of the cells of the innate and adaptive immune systems as well as the potential role of schistosome-associated factors as therapeutic modulators of immune disorders, including allergies, autoimmune diseases, and transplant immunopathology. We also discuss potential opportunities for targeting schistosome-induced immunoregulation for future translation to the clinical setting.

Bioinformatics analysis and characterization of a secretory cystatin from Thelohanellus kitauei

Thelohanellus kitauei, is a member of obligate parasitic myxozoans, which causes intestinal giant-cystic disease of common carp (Cyprinus carpio) and has resulted in significant economic losses in carp farms. Cystatin secreted by parasites can regulate the immune response of host to facilitate parasite's survival. In this study, the secretory TK-cystatin gene, encoding a protein of 120 amino acid residues (13.65 kDa), was cloned from T. kitauei genome. Phylogenetic analysis showed that TK-cystatin gene is closely related to the cystatin-A from Hydra vulgaris. Multiple sequence alignment revealed that TK-cystatin had three conserved motifs: N-terminal G19G20, Q73VVAG77, and C-terminal L102P103. Molecular docking between TK-cystatin and three cysteine proteases showed a lower binding energy (- 13 KJ/mol) with cathepsin L whereas a higher binding energy (- 8.6 KJ/mol) with cathepsin B. TK-cystatin gene was expressed in Escherichia coli. Activity assays revealed that TK-cystatin has stronger inhibitory activity on endopeptidases (papain and cathepsin L) and weaker inhibitory activity on exopeptidase (cathepsin B). TK-cystatin was stable under the condition of acidity or alkalinity or below 57 °C. This study laid a foundation for the design and development of the anti-T. kitauei vaccine in carp culture in the future.

Therapeutic efficacy of Schistosoma japonicum cystatin on sepsis-induced cardiomyopathy in a mouse model

BACKGROUND

Myocardial dysfunction is one of the most common complications of multiple organ failure in septic shock and significantly increases mortality in patients with sepsis. Although many studies having confirmed that helminth-derived proteins have strong immunomodulatory functions and could treat inflammatory diseases, there is no report on the therapeutic effect of Schistosoma japonicum-produced cystatin (Sj-Cys) on sepsis-induced cardiac dysfunction.

METHODS

A model of sepsis-induced myocardial injury was established by cecal ligation and puncture (CLP) in mice. Upon CLP operation, each mouse was intraperitoneally treated with 10 µg of recombinant Sj-Cys (rSj-Cys). Twelve hours after CLP, the systolic and diastolic functions of the left ventricular were examined by echocardiography. The levels of myoglobin (Mb), cardiac troponin I (cTnI), N-terminal pro-Brain Natriuretic peptide (NT-proBNP) in sera, and the activity of myeloperoxidase (MPO) in cardiac tissues were examined as biomarkers for heart injury. The heart tissue was collected for checking pathological changes, macrophages and pro-inflammatory cytokine levels. To address the signaling pathway involved in the anti-inflammatory effects of rSj-Cys, myeloid differentiation factor 88 (MyD88) was determined in heart tissue of mice with sepsis and LPS-stimulated H9C2 cardiomyocytes. In addition, the therapeutic effects of rSj-Cys on LPS-induced cardiomyocyte apoptosis were also detected. The levels of M1 biomarker iNOS and M2 biomarker Arg-1 were detected in heart tissue. The pro-inflammatory cytokines TNF-α and IL-6, and regulatory cytokines IL-10 and TGF-β were measured in sera and their mRNA levels in heart tissue of rSj-Cys-treated mice.

RESULTS

After rSj-Cys treatment, the sepsis-induced heart malfunction was largely improved. The inflammation and injury of heart tissue were significantly alleviated, characterized as significantly decreased infiltration of inflammatory cells in cardiac tissues and fiber swelling, reduced levels of Mb, cTnI and NT-proBNP in sera, and MPO activity in heart tissue. The therapeutic efficacy of rSj-Cys is associated with downregulated pro-inflammatory cytokines (TNF-α and IL-6) and upregulated regulatory inflammatory cytokines (IL-10 and TGF-β), possibly through inhibiting the LPS-MyD88 signal pathway.

CONCLUSIONS

RSj-Cys significantly reduced sepsis-induced cardiomyopathy and could be considered as a potential therapeutic agent for the prevention and treatment of sepsis associated cardiac dysfunction.

The effect of Triaenophorus nodulosus (Cestoda: Bothriocephalidea) infection on some biochemical parameters of the liver of Perca fluviatilis

Natural infection of 2 to 6-year-old perch with the cestode parasites Triaenophorus nodulosus was shown to have minor effects on the studied components of the antioxidant defense system, nucleic acids degradation, and carbohydrate metabolism enzymes in the liver of the fish. The level of infection of 1-4 parasite larvae per fish observed in wild population of perch was shown to be moderate in terms of its effect on the health of the host fish. The activity of hepatic enzymes β-galactosidase, β-glucosidase, cathepsin D, and glutathione S-transferase showed different responses in infected males and females, which indicates different potential resistance of fish to the stress exposure between genders.

Cystatin from Filarial Parasites Suppress the Clinical Symptoms and Pathology of Experimentally Induced Colitis in Mice by Inducing T-Regulatory Cells, B1-Cells, and Alternatively Activated Macrophages

Potential alternative therapeutic strategies for immune-mediated disorders are being increasingly recognized and are studied extensively. We previously reported the therapeutic potential of Brugia malayi derived recombinant cystatin (rBmaCys) in attenuating clinical symptoms of experimental colitis. The aim of this study was to elucidate the mechanisms involved in the rBmaCys-induced suppression of inflammation in the colon. Our results show that, the frequency of CD4⁺CD25⁺FoxP3⁺ regulatory T-cells was elevated in the colon and mesenteric lymph nodes. Similarly, the peritoneal macrophages recovered from the rBmaCys-treated colitis mice were alternatively activated and displayed reduced expression of TNF-α and IL-6. Another finding was significant increases in IgM⁺B1a-cells in the peritoneal cavity of mice following rBmaCys-treatment. These findings suggested that the regulatory cell network promoted by the rBmaCys in the colon and associated lymphoid tissues is important for its anti-inflammatory activity in the dextran sulfate sodium (DSS)-induced colitis mice.

The structure and function of Iristatin, a novel immunosuppressive tick salivary cystatin

To successfully feed, ticks inject pharmacoactive molecules into the vertebrate host including cystatin cysteine protease inhibitors. However, the molecular and cellular events modulated by tick saliva remain largely unknown. Here, we describe and characterize a novel immunomodulatory cystatin, Iristatin, which is upregulated in the salivary glands of feeding Ixodes ricinus ticks. We present the crystal structure of Iristatin at 1.76 Å resolution. Purified recombinant Iristatin inhibited the proteolytic activity of cathepsins L and C and diminished IL-2, IL-4, IL-9, and IFN-γ production by different T-cell populations, IL-6 and IL-9 production by mast cells, and nitric oxide production by macrophages. Furthermore, Iristatin inhibited OVA antigen-induced CD4+ T-cell proliferation and leukocyte recruitment in vivo and in vitro. Our results indicate that Iristatin affects wide range of anti-tick immune responses in the vertebrate host and may be exploitable as an immunotherapeutic.

Qualitative and quantitative proteomic analyses of Schistosoma japonicum eggs and egg-derived secretory-excretory proteins

BACKGROUND

Schistosome parasites lay up to a thousand eggs per day inside the veins of their mammalian hosts. The immature eggs deposited by females against endothelia of venules will embryonate within days. Approximately 30% of the eggs will migrate to the lumen of the intestine to continue the parasite life-cycle. Many eggs, however, are trapped in the liver and intestine causing the main pathology associated with schistosomiasis mansoni and japonica, the liver granulomatous response. Excretory-secretory egg proteins drive much of egg-induced pathogenesis of schistosomiasis mansoni, and Schistosoma japonicum induce a markedly distinct granulomatous response to that of S. mansoni.

METHODS

To explore the basis of variations in this responsiveness, we investigated the proteome of eggs of S. japonicum. Using mass spectrometry qualitative and quantitative (SWATH) analyses, we describe the protein composition of S. japonicum eggs secretory proteins (ESP), and the differential expression of proteins by fully mature and immature eggs, isolated from faeces and ex vivo adults.

RESULTS

Of 957 egg-related proteins identified, 95 were exclusively found in S. japonicum ESP which imply that they are accessible to host immune system effector elements. An in-silico analysis implies that ESP are able of stimulating the innate and adaptive immune system through several different pathways. While quantitative SWATH analysis revealed 124 proteins that are differentially expressed by mature and immature S. japonicum eggs, illuminating some important aspects of eggs biology and infection, we also show that mature eggs are more likely than immature eggs to stimulate host immune responses.

CONCLUSIONS

Here we present a list of potential targets that can be used to develop better strategies to avoid severe morbidity during S. japonicum infection, as well as improving diagnosis, treatment and control of schistosomiasis japonica.

Parasite-Derived Proteins for the Treatment of Allergies and Autoimmune Diseases

The morbidity associated with atopic diseases and immune dysregulation disorders such as asthma, food allergies, multiple sclerosis, atopic dermatitis, type 1 diabetes mellitus, and inflammatory bowel disease has been increasing all around the world over the past few decades. Although the roles of non-biological environmental factors and genetic factors in the etiopathology have been particularly emphasized, they do not fully explain the increase; for example, genetic factors in a population change very gradually. Epidemiological investigation has revealed that the increase also parallels a decrease in infectious diseases, especially parasitic infections. Thus, the reduced prevalence of parasitic infections may be another important reason for immune dysregulation. Parasites have co-evolved with the human immune system for a long time. Some parasite-derived immune-evasion molecules have been verified to reduce the incidence and harmfulness of atopic diseases in humans by modulating the immune response. More importantly, some parasite-derived products have been shown to inhibit the progression of inflammatory diseases and consequently alleviate their symptoms. Thus, parasites, and especially their products, may have potential applications in the treatment of autoimmune diseases. In this review, the potential of parasite-derived products and their analogs for use in the treatment of atopic diseases and immune dysregulation is summarized.

Functional characterization of single-domain cystatin-like cysteine proteinase inhibitors expressed by the trematode Fasciola hepatica

Cystatins are small, phylogenetically conserved proteins that are tight-binding inhibitors of cysteine proteinases. The liver fluke Fasciola hepatica uses a diverse set of cysteine proteinases of the papain superfamily for host invasion, immune evasion and nutrition, but little is known about the regulation of these enzymes. The aim of this work is to characterize the cystatin repertoire of F. hepatica. For this purpose, we first surveyed the available sequence databases, identifying three different F. hepatica single-domain cystatins. In agreement with the in silico predictions, at least three small proteins with cysteine proteinase binding activity were identified. Phylogenetic analyses showed that the three cystatins (named FhStf-1, -2 and -3) are members of the I25A subfamily (stefins). Whereas FhStf-1 grouped with classical stefins, FhStf-2 and 3 fell in a divergent stefin subgroup unusually featuring signal peptides. Recombinant rFhStf-1, -2 and -3 had potent inhibitory activity against F. hepatica cathepsin L cysteine proteinases but differed in their capacity to inhibit mammalian cathepsin B, L and C. FhStf-1 was localized in the F. hepatica reproductive organs (testes and ovary), and at the surface lamella of the adult gut, where it may regulate cysteine proteinases related with reproduction and digestion, respectively. FhStf-1 was also detected among F. hepatica excretion-secretion (E/S) products of adult flukes. This suggests that it is secreted by non-classical secretory pathway and that it may interact with host lysosomal cysteine proteinases.