Caspase-3-mediated apoptosis of human eosinophils by the tissue-invading helminth Paragonimus westermani

Regulation of immune response against third-stage Gnathostoma spinigerum larvae by human genes

Background

Gnathostomiasis is an important zoonosis in tropical areas that is mainly caused by third-stage Gnathostoma spinigerum larvae (G. spinigerum L3).

Objectives

This study aimed to prove whether G. spinigerum L3 produces extracellular vesicles (EVs) and investigate human gene profiles related to the immune response against the larvae.

Methods

We created an immune cell model using normal human peripheral blood mononuclear cells (PBMCs) co-cultured with the larvae for 1 and 3 days, respectively. The PBMCs were harvested for transcriptome sequencing analysis. The EV ultrastructure was examined in the larvae and the cultured medium.

Results

Extracellular vesicle-like particles were observed under the larval teguments and in the pellets in the medium. RNA-seq analysis revealed that 2,847 and 3,118 genes were significantly expressed on days 1 and 3 after culture, respectively. The downregulated genes on day 1 after culture were involved in pro-inflammatory cytokines, the complement system and apoptosis, whereas those on day 3 were involved in T cell-dependent B cell activation and wound healing. Significantly upregulated genes related to cell proliferation, activation and development, as well as cytotoxicity, were observed on day 1, and genes regulating T cell maturation, granulocyte function, nuclear factor-κB and toll-like receptor pathways were predominantly observed on day 3 after culture.

Conclusion

G. spinigerum L3 produces EV-like particles and releases them into the excretory-secretory products. Overall, genotypic findings during our 3-day observation revealed that most significant gene expressions were related to T and B cell signalling, driving T helper 2 cells related to chronic infection, immune evasion of the larvae, and the pathogenesis of gnathostomiasis. Further in-depth studies are necessary to clarify gene functions in the pathogenesis and immune evasion mechanisms of the infective larvae.

Upregulated galectin-1 in Angiostrongylus cantonensis L5 reduces body fat and increases oxidative stress tolerance

Background

Angiostrongylus cantonensis L5, parasitizing human cerebrospinal fluid, causes eosinophilic meningitis, which is attributed to tissue inflammatory responses caused primarily by the high percentage of eosinophils. Eosinophils are also involved in killing helminths, using the peroxidative oxidation and hydrogen peroxide (H₂O₂) generated by dismutation of superoxide produced during respiratory burst. In contrast, helminthic worms have evolved to attenuate eosinophil-mediated tissue inflammatory responses for their survival. In previous study, we demonstrated the extracellular function of Acan-Gal-1 in inducing the apoptosis of macrophages. Here, the intracellular functions of Acan-Gal-1 were investigated, aiming to further reveal the mechanism involved in A. cantonensis L5 worms surviving inflammatory responses in the human central nervous system.

Methods

In this study, a model organism, Caenorhabditis elegans, was used as a surrogate to investigate the intracellular functions of Acan-Gal-1 in protecting the worm from its host’s immune attacks. First, structural characterization of Acan-Gal-1 was analyzed using bioinformatics; second, qRT-PCR was used to monitor the stage specificity of Acan-gal-1 expression in A. cantonensis. Microinjections were performed to detect the tissue specificity of lec-1 expression, the homolog of Acan-gal-1 in C. elegans. Third, microinjection was performed to develop Acan-gal-1::rfp transgenic worms. Then, oxidative stress assay and Oil Red O fat staining were used to determine the functions of Acan-Gal-1 in C. elegans.

Results

The results of detecting the stage specificity of Acan-gal-1 expression showed that Acan-Gal-1 was upregulated in both L5 and adult worms. Detection of the tissue specificity showed that the homolog of Acan-gal-1 in C. elegans, lec-1 was expressed ubiquitously and mainly localized in cuticle. Investigating the intracellular functions of Acan-Gal-1 in the surrogate C. elegans showed that N2 worms expressing pCe-lec-1::Acan-gal-1::rfp, with lipid deposition reduced, were significantly resistant to oxidative stress; lec-1 mutant worms, where lipid deposition increased, showed susceptible to oxidative stress, and this phenotype could be rescued by expressing pCe-lec-1::Acan-gal-1::rfp. Expressing pCe-lec-1::Acan-gal-1::rfp or lec-1 RNAi in fat-6;fat-7 double-mutant worms, where fat stores were reduced, had no significant effect on the oxidative stress tolerance.

Conclusion

In C. elegans worms, upregulated Acan-Gal-1 plays a defensive role against damage due to oxidative stress for worm survival by reducing fat deposition. This might indicate the mechanism by which A. cantonensis L5 worms, with upregulated Acan-Gal-1, survive the immune attack of eosinophils in the human central nervous system.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-022-05171-4.

Apoptosis of Eosinophil Granulocytes

Simple Summary

Eosinophil granulocytes (eosinophils) belong to the family of white blood cells that play important roles in the development of asthma and various types of allergy. Eosinophils are cells with a diameter of 12–17 µm and they originate from myeloid precursors. They were discovered by Paul Ehrlich in 1879 in the process of staining fixed blood smears with aniline dyes. Apoptosis (programmed cell death) is the process by which cells lose their functionality. Therefore, it is very important to study the apoptosis of eosinophils and their survival factors to understand how to develop new drugs based on the modulation of eosinophil apoptosis for the treatment of asthma and allergic diseases.

Abstract

In the past 10 years, the number of people in the Czech Republic with allergies has doubled to over three million. Allergic pollen catarrh, constitutional dermatitis and asthma are the allergic disorders most often diagnosed. Genuine food allergies today affect 6–8% of nursing infants, 3–5% of small children, and 2–4% of adults. These disorders are connected with eosinophil granulocytes and their apoptosis. Eosinophil granulocytes are postmitotic leukocytes containing a number of histotoxic substances that contribute to the initiation and continuation of allergic inflammatory reactions. Eosinophilia results from the disruption of the standard half-life of eosinophils by the expression of mechanisms that block the apoptosis of eosinophils, leading to the development of chronic inflammation. Glucocorticoids are used as a strong acting anti-inflammatory medicine in the treatment of hypereosinophilia. The removal of eosinophils by the mechanism of apoptosis is the effect of this process. This work sums up the contemporary knowledge concerning the apoptosis of eosinophils, its role in the aforementioned disorders, and the indications for the use of glucocorticoids in their related therapies.

Downregulated RPS-30 in Angiostrongylus cantonensis L5 plays a defensive role against damage due to oxidative stress

Background

Eosinophilic meningitis, caused by fifth-stage larvae of the nematode (roundworm) Angiostrongylus cantonensis, is mainly attributed to the contribution of eosinophils to tissue inflammatory responses in helminthic infections. Eosinophils are associated with the killing of helminths via peroxidative oxidation and hydrogen peroxide generated by the dismutation of superoxide produced during respiratory bursts. In contrast, when residing in the host with high level of eosinophils, helminthic worms have evolved to attenuate eosinophil-mediated tissue inflammatory responses for their survival in the hosts. In a previous study we demonstrated that the expression of the A. cantonensis RPS 30 gene (Acan-rps-30) was significantly downregulated in A. cantonensis L5 roundworms residing in cerebrospinal fluid with a high level of eosinophils. Acan-RPS-30 is a protein homologous to the human Fau protein that plays a pro-apoptotic regulatory role and may function in protecting worms from oxidative stress.

Methods

The isolation and structural characterization of Acan-RPS-30 were performed using rapid amplification of cDNA ends (RACE), genome walking and bioinformatics. Quantitative real-time-PCR and microinjection were used to detect the expression patterns of Acan-rps-30. Feeding RNA interference (RNAi) was used to knockdown the apoptosis gene ced-3. Microinjection was performed to construct transgenic worms. An oxidative stress assay was used to determine the functions of Acan-RPS-30.

Results

Our results showed that Acan-RPS-30 consisted of 130 amino acids. It was grouped into clade V with C. elegans in the phylogenetic analysis. It was expressed ubiquitously in worms and was downregulated in both L5 larvae and adult A. cantonensis. Worms expressing pCe-rps30::Acan-rps-30::rfp, with the refractile “button-like” apoptotic corpses, were susceptible to oxidative stress. Apoptosis genes ced-3 and ced-4 were both upregulated in the transgenic worms. The phenotype susceptible to oxidative stress could be converted with a ced-3 defective mutation and RNAi. rps-30^−/− mutant worms were resistant to oxidative stress, with ced-3 and ced-4 both downregulated. The oxidative stress-resistant phenotype could be rescued and inhibited by through the expression of pCe-rps30::Acan-rps-30::rfp in rps-3^−/− mutant worms.

Conclusion

In C. elegans worms, downregulated RPS-30 plays a defensive role against damage due to oxidative stress, facilitating worm survival by regulating downregulated ced-3. This observation may indicate the mechanism by which A. cantonensis L5 worms, with downregulated Acan-RPS-30, survive in the central nervous system of humans from the immune response of eosinophils.

Graphic abstract

Dioscin Promotes Prostate Cancer Cell Apoptosis and Inhibits Cell Invasion by Increasing SHP1 Phosphorylation and Suppressing the Subsequent MAPK Signaling Pathway

Dioscin possesses antioxidant effects and has anticancer ability in many solid tumors including prostate cancer (PCa). Nevertheless, its effect and mechanism of anti-PCa action remain unclear. The tyrosine protein phosphatase SHP1, which contains an oxidation-sensitive domain, has been confirmed as a target for multicancer treatment. Further studies are needed to determine whether dioscin inhibits PCa through SHP1. We performed in vitro studies using androgen-sensitive (LNCaP) and androgen-independent (LNCaP -C81) cells to investigate the anticancer effects and possible mechanisms of dioscin after administering interleukin-6 (IL-6) and dihydrotestosterone (DHT). Our results show that dioscin inhibited cell growth and invasion by increasing SHP1 phosphorylation [p-SHP1 (Y536)] and inhibiting the subsequent P38 mitogen-activated protein kinase signaling pathway. Further in vivo studies confirmed that dioscin promoted caspase-3 and Bad-related cell apoptosis in these two cell lines. Our research suggests that the anticancer effects of dioscin on PCa may occur through SHP1. Dioscin may be useful to treat androgen-sensitive and independent PCa in the future.

Paragonimiasis

Paragonimiasis is a zoonotic disease caused by lung flukes of the genus Paragonimus. Humans usually become infected by eating freshwater crabs or crayfish containing encysted metacercariae of these worms. However, an alternative route of infection exists: ingestion of raw meat from a mammalian paratenic host. Adult worms normally occur in pairs in cysts in the lungs from which they void their eggs via air passages. The pulmonary form is typical in cases of human infection due to P. westermani, P. heterotremus, and a few other species (Table 5.1). Worms may occupy other sites in the body, notably the brain, but lung flukes have made their presence felt in almost every organ. Ectopic paragonimiasis is particularly common when infection is due to members of the P. skrjabini complex (Table 5.1). Human paragonimiasis occurs primarily in the tropics and subtropics of Asia, Africa, and the Americas, with different species being responsible in different areas (Table 5.1).

Helminth-induced apoptosis: a silent strategy for immunosuppression

During microbial infections, both innate and adaptive immunity are activated. Viruses and bacteria usually induce an acute inflammation in the first setting of infection, which helps the eliciting an effective immune response. In contrast, macroparasites such as helminths are a highly successful group of invaders known to be capable of maintaining a chronic infestation with the minimum instigation. Undoubtedly, generating such an immunoregulatory environment requires the exploitation of various immunosuppressive mechanisms to debilitate host immunity supporting their survival and replication. Several mechanisms have been recognized whereby helminths prolong their infections including an increase of immunoregulatory cells, inhibition of Th1 or Th2 responses, targeting pattern recognition receptors (PRRs) and lowering the immune cells quantity via induction of apoptosis. Apoptosis is a programmed intracellular process involving a series of consecutive downstream signalling event evolved to cell death. It plays a pivotal role in several immunological reactions in particular deletion of autoreactive immune cells. Helminth-triggered apoptosis in immune cells exhausts host immunity, which paves the way for generating a permissive environment and chronic infection. This review provides a compilation of recent investigations discussing the apoptotic mechanisms exploited by different worms and the immunological consequences of immune cell death. Finally, the anti-cancer effects of some worm-derived molecules due to their apoptotic effects are discussed, highlighting as potentially druggable candidates to combat cancer.

Anisakis pegreffii (Nematoda: Anisakidae) products modulate oxidative stress and apoptosis-related biomarkers in human cell lines

BACKGROUND

In countries with elevated prevalence of zoonotic anisakiasis and high awareness of this parasitosis, a considerable number of cases that associate Anisakis sp. (Nematoda, Anisakidae) and different bowel carcinomas have been described. Although neoplasia and embedded larvae were observed sharing the common site affected by chronic inflammation, no association between the nematode and malignancy were directly proved. Similarly, no data are available about the effect of secretory and excretory products of infecting larvae at the host's cellular level, except in respect to allergenic interaction.

METHODS

To test the mechanisms by which human non-immune cells respond to the larvae, we exposed the fibroblast cell line HS-68 to two Anisakis products (ES, excretory/secretory products; and EC, crude extract) and evaluated molecular markers related to stress response, oxidative stress, inflammation and apoptosis, such as p53, HSP70, TNF-α, c-jun and c-fos, employing cell viability assay, spectrophotometry, immunoblotting and qPCR.

RESULTS

Both Anisakis products led to increased production of reactive oxygen species (ROS), especially in EC-treated cells. While the ES treatment induces activation of kinases suggesting inflammation and cell proliferation (or inhibition of apoptosis), in EC-treated cells, other signaling pathways indicate the inhibition of apoptosis, marked by strong upregulation of Hsp70. Elevated induction of p53 in fibroblasts treated by both Anisakis products, suggests a significantly negative effect on the host DNA.

CONCLUSIONS

This study shows that in vitro cell response to Anisakis products can result in at least two different scenarios, which in both cases lead to inflammation and DNA damage. Although these preliminary results are far from proving a relationship between the parasite and cancer, they are the first to support the existence of conditions where such changes are feasible.

Fasciola hepatica induces eosinophil apoptosis in the migratory and biliary stages of infection in sheep

The aim of the present work was to evaluate the number of apoptotic eosinophils in the livers of sheep experimentally infected with Fasciola hepatica during the migratory and biliary stages of infection. Four groups (n=5) of sheep were used; groups 1-3 were orally infected with 200 metacercariae (mc) and sacrificed at 8 and 28 days post-infection (dpi), and 17 weeks post-infection (wpi), respectively. Group 4 was used as an uninfected control. Apoptosis was detected using immunohistochemistry with a polyclonal antibody against anti-active caspase-3, and transmission electron microscopy (TEM). Eosinophils were identified using the Hansel stain in serial sections for caspase-3, and by ultrastructural features using TEM. At 8 and 28 dpi, numerous caspase-3(+) eosinophils were mainly found at the periphery of acute hepatic necrotic foci. The percentage of caspase -3(+) apoptotic eosinophils in the periphery of necrotic foci was high (46.1-53.9) at 8 and 28 dpi, respectively, and decreased in granulomas found at 28 dpi (6%). Transmission electron microscopy confirmed the presence of apoptotic eosinophils in hepatic lesions at 8 and 28 dpi. At 17 wpi, apoptotic eosinophils were detected in the infiltrate surrounding some enlarged bile ducts containing adult flukes. This is the first report of apoptosis induced by F. hepatica in sheep and the first study reporting apoptosis in eosinophils in hepatic inflammatory infiltrates in vivo. The high number of apoptotic eosinophils in acute necrotic tracts during the migratory and biliary stages of infection suggests that eosinophil apoptosis may play a role in F. hepatica survival during different stages of infection.

Genome-wide analysis of regulatory proteases sequences identified through bioinformatics data mining in Taenia solium

Background

Cysticercosis remains a major neglected tropical disease of humanity in many regions, especially in sub-Saharan Africa, Central America and elsewhere. Owing to the emerging drug resistance and the inability of current drugs to prevent re-infection, identification of novel vaccines and chemotherapeutic agents against Taenia solium and related helminth pathogens is a public health priority. The T. solium genome and the predicted proteome were reported recently, providing a wealth of information from which new interventional targets might be identified. In order to characterize and classify the entire repertoire of protease-encoding genes of T. solium, which act fundamental biological roles in all life processes, we analyzed the predicted proteins of this cestode through a combination of bioinformatics tools. Functional annotation was performed to yield insights into the signaling processes relevant to the complex developmental cycle of this tapeworm and to highlight a suite of the proteases as potential intervention targets.

Results

Within the genome of this helminth parasite, we identified 200 open reading frames encoding proteases from five clans, which correspond to 1.68% of the 11,902 protein-encoding genes predicted to be present in its genome. These proteases include calpains, cytosolic, mitochondrial signal peptidases, ubiquitylation related proteins, and others. Many not only show significant similarity to proteases in the Conserved Domain Database but have conserved active sites and catalytic domains. KEGG Automatic Annotation Server (KAAS) analysis indicated that ~60% of these proteases share strong sequence identities with proteins of the KEGG database, which are involved in human disease, metabolic pathways, genetic information processes, cellular processes, environmental information processes and organismal systems. Also, we identified signal peptides and transmembrane helices through comparative analysis with classes of important regulatory proteases. Phylogenetic analysis using Bayes approach provided support for inferring functional divergence among regulatory cysteine and serine proteases.

Conclusion

Numerous putative proteases were identified for the first time in T. solium, and important regulatory proteases have been predicted. This comprehensive analysis not only complements the growing knowledge base of proteolytic enzymes, but also provides a platform from which to expand knowledge of cestode proteases and to explore their biochemistry and potential as intervention targets.

Electronic supplementary material

The online version of this article (doi: 10.1186/1471-2164-15-428) contains supplementary material, which is available to authorized users.

Paragonimiasis

Paragonimiasis is a zoonotic disease caused by lung flukes of the genus Paragonimus. Humans usually become infected by eating freshwater crabs or crayfish containing encysted metacercariae of these worms. However, an alternative route of infection exists: ingestion of raw meat from a mammalian paratenic host. Adult worms normally occur in pairs in cysts in the lungs from which they void their eggs via air passages. The pulmonary form is typical in cases of human infection due to P. westermani, P. heterotremus, and a few other species (Table 5.1). Worms may occupy other sites in the body, notably the brain, but lung flukes have made their presence felt in almost every organ. Ectopic paragonimiasis is particularly common when infection is due to members of the P. skrjabini complex (Table 5.1). Human paragonimiasis occurs primarily in the tropics and subtropics of Asia, Africa, and the Americas, with different species being responsible in different areas (Table 5.1).

Staphylococcus aureus induces eosinophil cell death mediated by α-hemolysin

Staphylococcus aureus, a major human pathogen, exacerbates allergic disorders, including atopic dermatitis, nasal polyps and asthma, which are characterized by tissue eosinophilia. Eosinophils, via their destructive granule contents, can cause significant tissue damage, resulting in inflammation and further recruitment of inflammatory cells. We hypothesised that the relationship between S. aureus and eosinophils may contribute to disease pathology. We found that supernatants from S. aureus (SH1000 strain) cultures cause rapid and profound eosinophil necrosis, resulting in dramatic cell loss within 2 hours. This is in marked contrast to neutrophil granulocytes where no significant cell death was observed (at equivalent dilutions). Supernatants prepared from a strain deficient in the accessory gene regulator (agr) that produces reduced levels of many important virulence factors, including the abundantly produced α-hemolysin (Hla), failed to induce eosinophil death. The role of Hla in mediating eosinophil death was investigated using both an Hla deficient SH1000-modified strain, which did not induce eosinophil death, and purified Hla, which induced concentration-dependent eosinophil death via both apoptosis and necrosis. We conclude that S. aureus Hla induces aberrant eosinophil cell death in vitro and that this may increase tissue injury in allergic disease.

Nitric oxide induces apoptosis in GM-CSF-treated eosinophils via caspase-6-dependent lamin and DNA fragmentation

Asthma is characterized by accumulation of eosinophils in the lungs and delayed apoptosis may be one mechanism leading to eosinophilia. Nitric oxide (NO), present in inflamed lungs, has been shown to possess both anti- and proeosinophilic properties. We previously showed that NO induces apoptosis in the presence of survival prolonging cytokine IL-5 in human eosinophils. In the present study, we examined the intracellular mechanisms of NO-induced apoptosis in granulocyte macrophage-colony stimulating factor (GM-CSF)-treated eosinophils concentrating on the role of caspases and calpains. Eosinophils were isolated from human blood and apoptosis was determined by relative DNA fragmentation assay, morphological analysis and/or Annexin-V FITC assay. We showed that NO-donor S-nitroso-N-acetyl-d,l-penicillamine (SNAP) induced apoptosis in GM-CSF-treated eosinophils. SNAP-induced DNA fragmentation was totally prevented by an inhibitor of caspase-6 (Z-VEID-FMK). Decreased levels of caspase-6 proenzyme and increased amounts of cleaved lamin A/C in SNAP-treated cells indicated activation of caspase-6. Furthermore, SNAP-induced lamin A/C and B fragmentation was totally abolished by an inhibitor of caspase-6. According to our results, caspase-6 mediates lamin and DNA fragmentation also in spontaneously dying eosinophils. Inhibitor of calpains prevented most of DNA fragmentation related to spontaneous apoptosis but had no effect in eosinophils undergoing NO-induced apoptosis. In the present study we showed that caspase-6 is essential for the executive phase involving lamin and DNA fragmentation in both NO-induced and spontaneous eosinophil apoptosis. However, differences in the involvement of calpains suggest that the intracellular signalling in NO-induced apoptosis has specific features at the level of proteases. This study demonstrates new mechanisms for NO-induced and spontaneous apoptosis in human eosinophils.

Eosinophil-mediated tissue inflammatory responses in helminth infection

Eosinophilic leukocytes function in host protection against parasitic worms. In turn, helminthic parasites harbor specific molecules to evade or paralyze eosinophil-associated host immune responses; these molecules facilitate the migration and survival of parasitic helminths in vivo. This competition between eosinophil and worm leads to stable equilibria between them. An understanding of such dynamic host-eosinophil interactions will help us to uncover mechanisms of cross talk between host and parasite in helminth infection. In this review, we examine recent findings regarding the innate immune responses of eosinophils to helminthic parasites, and discuss the implications of these findings in terms of eosinophil-mediated tissue inflammation in helminth infection.

North American paragonimiasis (Caused by Paragonimus kellicotti) in the context of global paragonimiasis

Paragonimus species are highly evolved parasites with a complex life cycle that involves at least three different hosts, i.e., snails, crustaceans, and mammals. The adult forms of Paragonimus species reside and mate in the lungs of a variety of permissive mammalian hosts, including humans. Although human paragonimiasis is uncommonly encountered in North America, both autochthonous and imported disease may be encountered. Paragonimus kellicotti, the species endemic to North America, is a well-known pathogen in wild and domestic animals. Five patients with North American paragonimiasis have been reported in the recent medical literature. The biologic, clinical, radiologic, and laboratory features of paragonimiasis are reviewed, with emphasis on North American paragonimiasis whenever possible.

A 27 kDa cysteine protease secreted by newly excysted Paragonimus westermani metacercariae induces superoxide anion production and degranulation of human eosinophils

Eosinophil degranulation plays a crucial role in tissue inflammatory reactions associated with helminth parasitic infections and allergic diseases. Paragonimus westermani, a lung fluke causing human paragonimiasis, secretes a large amount of cysteine proteases, which are involved in nutrient uptake, tissue invasion, and modulation of hos's immune responses. There is, however, limited information about the response of eosinophils to direct stimulation by cysteine proteases (CP) secreted by P. westermani. In the present study, we tested whether degranulation and superoxide production from human eosinophils can be induced by stimulation of the 2 CP (27 kDa and 28 kDa) purified from excretory-secretory products (ESP) of P. westermani newly excysted metacercariae (PwNEM). A large quantity of eosinophil-derived neurotoxin (EDN) was detected in the culture supernatant when human eosinophils isolated from the peripheral blood were incubated with the purified 27 kDa CP. Furthermore, the 27 kDa CP induced superoxide anion production by eosinophils in time- and dose-dependent manners. In contrast, the purified 28 kDa CP did not induce superoxide production and degranulation. These findings suggest that the 27 kDa CP secreted by PwNEM induces superoxide production and degranulation of human eosinophils, which may be involved in eosinophil-mediated tissue inflammatory responses during the larval migration in human paragonimiasis.

Trichomonas vaginalis: Reactive oxygen species mediates caspase-3 dependent apoptosis of human neutrophils

There are many neutrophils in the vaginal discharge from women infected with Trichomonas vaginalis. The aim of our study was to determine whether human neutrophil apoptosis may be regulated by reactive oxygen species (ROS) in response to trichomonads infection. Incubation of human neutrophils with live trichomonads caused marked receptor shedding of CD16, decrease of mitochondrial membrane potential (MMP) and caspase-3 activation in human neutrophils. These proapoptotic effects of T. vaginalis on neutrophils were inhibited by pretreatment of neutrophils with an inhibitor of NADPH oxidase, diphenyleneiodonium chloride (DPI), suggesting an important role of intracellular ROS accumulation in T. vaginalis-triggered apoptosis. Indeed, large amounts of ROS levels were detected in neutrophils incubated with live trichomonads, and were also effectively inhibited by DPI. However, pan-caspase inhibitor z-VAD-fmk or caspase-3 inhibitor z-DEVD-fmk did not affect T. vaginalis-induced ROS generation in neutrophils. These results suggest that ROS-dependent caspase-3 activation plays an important role in apoptosis of human neutrophils induced by T. vaginalis.

Heligmosomoides polygyrus infection down-regulates eotaxin concentration and CCR3 expression on lung eosinophils in murine allergic pulmonary inflammation

There is growing evidence that helminth infections might suppress allergic responses by mechanisms potentially involving regulatory T lymphocytes, cytokines, helminth molecules and polyclonal IgE. Heligmosomoides polygyrus infection in mice is associated with reduced local and systemic immune responses, thus providing an excellent model to study the mechanisms of immune regulation. In this research, we examined the way that nematode infection modulates the influx of eosinophils into the airways of asthmatic mice. We observed a reduction in the total number and percentage of lung eosinophils that coincided with decreased levels of eotaxin in bronchoalveolar lavage fluid (BALF), lower expression of the CCR3 receptor on eosinophils and impaired chemotaxis of these cells toward eotaxin. We conclude that allergen-induced immune response was down-regulated as production of Th1 (IFN-gamma)-, Th2 (IL-4, IL-5)- and Treg (IL-10)-related cytokines as well as IL-6 and TNF-alpha was diminished upon nematode infection. We postulate that attenuation of allergic inflammation during H. polygyrus infection is a consequence of the dichotomy of the immune response in the face of concurrent antigenic challenge.

Excretory-secretory products from Fasciola hepatica induce eosinophil apoptosis by a caspase-dependent mechanism

Eosinophils (Eo) are known to be important effector cells in the host defense against helminth parasites. Excretory-secretory products (ESP) released by helminths have shown wide immunomodulatory properties, such as the induction of cellular apoptosis. We investigated the ability of ESP from Fasciola hepatica to induce Eo apoptosis. In this work, we observed that ESP induced an early apoptosis of rat peritoneal eosinophils and that this phenomenon was time- and concentration-dependent. Furthermore, we demonstrated that activation of protein tyrosine kinases (TyrK) and caspases were necessary to mediate the Eo apoptosis induced by the ESP, and that carbohydrate components present in these antigens were involved in this effect. We have described for the first time the ability of ESP from F. hepatica to modify the viability of Eo by apoptosis induction. Besides that, we have observed Eo apoptosis in the liver of rats 21 days after F. hepatica infection. The diminution in Eo survival in early infection could be a parasite strategy in order to prevent a host immune response.

Critical roles for excretory-secretory cysteine proteases during tissue invasion of Paragonimus westermani newly excysted metacercariae

Paragonimus westermani is a trematode parasite, which causes pulmonary and/or extrapulmonary granulomatous disease in humans. Successful invasion of the host tissue is critical for the survival of this tissue-invasive parasite. The enzymatic hydrolysis of host proteins is clearly a prerequisite of this process. In this study, we have investigated the functional roles of the excretory-secretory cysteine proteases of P. westermani newly excysted metacercariae (PwNEM) in tissue invasion. The 27 and 28 kDa enzymes (PwMc27 and PwMc28) purified from PwNEM excretory-secretory products (ESP), preferentially degraded fibrillar proteins, but not globular proteins. PwMc28 significantly facilitated the invasion of PwNEM into mouse peritoneum, whereas a diffusible cysteine protease inhibitor, trans-epoxysuccinyl-L-leuciloamido-(4-guanidino) butane (E-64) inhibited this process dose-dependently. Two distinct isoforms of PwMc28 (PwMc28a and PwMc28b), which exhibited two amino acid differences in their mature domains, were identified by tandem mass spectrometry and sequence analysis. Both enzymes were localized at the tegument on the anterior border and on the oral sucker, which suggests excretion-secretion via exocytosis or via the excretory canal network. The mRNA transcripts of PwMc28a and b were expressed abundantly during the active invasion/migration through the host's tissues, suggesting their relevant function to tissue invasion/migration in the definitive host.

Macrophageal/microglial cell activation and cerebral injury induced by excretory–secretory products secreted by Paragonimus westermani

Cerebral paragonimiasis causes various neurological disorders including seizures, visual impairment and hemiplegia. The excretory-secretory product (ESP) released by Paragonimus westermani has a cysteine protease activity and plays important roles in its migration in the host tissue and modulation of host immune responses. To gain more insight into the pathogenesis of ESP in the brain, we investigated the inflammatory reaction and cerebral injury following microinjection of ESP into rat striatum. The size of injury was maximally observed 3 days after microinjection of ESP and then declined to control levels as astrocytes have repopulated the injury. ED1-positive monocytes and microglia were confluently found inside the injury. The mRNA expression of inducible nitric oxide synthase (iNOS) occurred as early as 9h after ESP injection and then declined to control levels within 1 day. The iNOS inhibitor aminoguanidine largely decreased the expression of iNOS but did not reduce the size of lesion caused by ESP. Interestingly, however, heat inactivation of ESP caused a decrease of injury formation with no altered expression of iNOS. The data indicate that ESP produces brain tissue injury by recruiting activated monocytes/microglia via heat-labile protease activity.

Identification of immunodominant excretory–secretory cysteine proteases of adultParagonimus westermani by proteome analysis

Paragonimus westermani causes inflammatory lung disease in humans. The parasite excretes a host of biologically active molecules, which are thought to be involved in pathophysiological and immunological events during infection. Analyses of the 2-DE protein profiles of the excretory-secretory products (ESP) of adult P. westermani revealed approximately 147 protein spots, at least 15 of which were identified as cysteine proteases (CPs), at pHs between 4.5 and 8.5, and molecular weights (MWs) between 27 and 35 kDa. An additional three CPs (designated as PwCP-3, -8 and -11) were newly recognized by TOF/TOF MS. Their molecular biological information, which shared a high level sequence homology, was elucidated. The majority of the CPs reacted strongly with sera from paragonimiasis patients. When we observed the chronological changes in the antibody responses of the respective CPs against canine sera collected serially at 1, 3, 5, 7, 11 and 14 wk after experimental infection, these molecules exhibited a multiplicity of distinct immune recognition patterns. Our results clearly showed that P. westermani adult ESP were principally composed of excretory-secretory CPs, and that these CPs may exert effects not only on host tissue degradation and nutrient uptake, but also on the immune-regulating cells via synergistic and independent interactions.

Eosinophilia: Causes and pathobiology in persons with prior exposures in tropical areas with an emphasis on parasitic infections

Eosinophilia in patients exposed to tropical or subtropical environments is caused most commonly by helminth (worm) infections. Besides a detailed exposure history, the diagnostic approach must consider other infections and noninfectious causes of eosinophilia, as treatments for many of these disorders differ.