Excretory-secretory product of newly excysted metacercariae of Paragonimus westermani directly induces eosinophil apoptosis

Gastric lesions in dolphins stranded along the Eastern Adriatic coast

Stranded cetaceans are often found with gastric lesions associated with the presence of parasites; most frequently, nematodes of the genus Anisakis and the heterophyd digenean trematode Pholeter gastrophilus. In this study, we present histopathology mainly (but not exclusively) related to these 2 parasite species. Macroscopically, lesions associated with the presence of Anisakis spp. were characterised by the presence of ulcers within the gastric mucosa, while the digenean P. gastrophilus was found within large submucosal fibrotic nodules in the gastric wall. Anisakis-induced alterations included severe ulcerative gastritis with mixed inflammatory infiltrate often associated with colonies of bacteria, and mild to moderate granulomatous gastritis with eosinophilic infiltrate. P. gastrophilus-associated lesions were characterised by fibrogranulomatous gastritis with mixed inflammatory infiltrate. Additionally, immunohistochemical (IHC) analysis of P. gastrophilus lesions was consistent with the histopathologic findings, revealing inflammation-mediated stimulation. IHC-positive localisation of CD3+, iNOS+ and caspase-3+ cells suggests intensive accumulation of cytotoxic T-cells, proinflammatory cytokines and execution-phase of cell apoptosis at the parasitized area. In contrast, mechanical damage, rather than visible inflammatory response could be observed at the site of attachment of Braunina cordiformis recorded in 4 animals. Lesions not associated with the presence of parasites were mostly characterised by focal loss of superficial epithelial cells and accumulation of brown hemosiderin-like pigment or fibrous gastritis with lymphoplasmacytic infiltrate. In light of these results, we argue that observed 'tolerant' host-parasite interactions that led toward gastric lesions do not represent the cause of death and stranding of cetaceans included in this study.

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.

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.

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.

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.

Excretory-Secretory Products Produced by Paragonimus westermani Differentially Regulate the Nitric Oxide Production and Viability of Microglial Cells

BACKGROUND

Tissue-invading helminth parasites secrete a large amount of cysteine proteases that may play critical roles in tissue invasion and immune modulation. However, roles of excretory-secretory products (ESP) secreted by Paragonimus westermani in the activation and death of microglial cells in brain are poorly understood.

OBJECTIVES

In the present study, we investigated whether ESP could regulate microglial nitric oxide (NO) production and viability.

METHODS

The NO production and cell viability were assessed by respectively measuring the formation of nitrite and the release of lactate dehyrogenase.

RESULTS

At a low (0.2 microg/ml) concentration, ESP significantly stimulated NO production with no apparent cell injury or death in cultured microglial cells. However, at high (> or =2 microg/ml) concentrations, ESP induced severe cell death. Inhibition of inducible NO synthase significantly reduced the NO productivity, but not cytotoxicity, of ESP. Similarly, inhibitors of the extracellular signal-regulated kinase, p38 and nuclear factor kappa B also blocked only the NO productivity of ESP. Interestingly, heat inactivation did not hamper the ability of ESP to stimulate microglial NO production. Similarly, pretreatment with thiol-crosslinking reagents dramatically reduced both proteolytic activity and cytotoxicity of ESP, but did not alter NO production in microglial cells. Interestingly, although cysteine protease competitive inhibitors and thiol-alkylating reagents markedly reduced the proteolytic activity of ESP, they did not influence the NO productivity and cytotoxicity of ESP.

CONCLUSION

The present results indicate that the NO production and cytotoxicity by ESP may be differentially regulated via unknown mechanisms, not related with cysteine protease activity.

Cysteine protease secreted by Paragonimus westermani attenuates effector functions of human eosinophils stimulated with immunoglobulin G

An immunoglobulin G (IgG)-coated surface, such as that found on helminth parasites, is one of the most effective physiologic stimuli for eosinophil activation. The cysteine proteases secreted by tissue-invasive helminth larvae play an important role in evasion of the immune response by degrading the host immunoglobulins. In this study, we investigated whether cysteine proteases in the excretory-secretory product (ESP) produced by Paragonimus westermani newly excysted metacercariae (PwNEM), which cause pulmonary or extrapulmonary paragonimiasis in human beings, could modify effector functions of human eosinophils stimulated with IgG. We coated 96-well plates with human IgG in the absence or presence of the ESP produced by PwNEM. When eosinophils were incubated in the wells coated with IgG in the presence of the ESP, eosinophil degranulation and superoxide production were significantly reduced compared with results for cells incubated in wells coated with IgG alone. This inhibitory effect of the ESP on IgG-induced superoxide production was dose dependent and was significantly abolished by pretreatment of the ESP with heat. These findings suggest that the cysteine proteases secreted by PwNEM attenuate both activation and degranulation of eosinophils stimulated with IgG. Thus, the cysteine proteases produced by tissue-invasive helminth larvae play crucial roles in evasion of IgG-dependent eosinophil helminthotoxicity and in reduction of eosinophil-associated tissue inflammation during the migratory period.

Proteolytic activity of cysteine protease in excretory-secretory product of Paragonimus westermani newly excysted metacercariae pivotally regulates IL-8 production of human eosinophils

This study investigated the effect of the excretory-secretory product (ESP) of Paragonimus westermani newly excysted metacercariae (PwNEM) on IL-8 production of human mature eosinophils. Treatment of eosinophils with lower concentrations (0.3 and 1 microg/ml) of the ESP significantly (P < 0.01) induced IL-8 production, whereas treatment of cells with higher concentrations (3 and 10 microg/ml) did not. This effect of the ESP was concentration-dependent. Interestingly, the amount of IL-8 production released into the culture supernatants was inversely correlated with the rate of eosinophil survival. When eosinophils were cultured with the same concentrations of the ESP for 24 h, the ESP resulted in eosinophil death in a dose-dependent manner. To investigate whether high proteolytic activity of proteases in the ESP could cause little production of IL-8, 10 microg/ml of ESP was pretreated with heat at 100 degrees C for 10 min or 56 degrees C for 30 min to reduce its proteolytic activity. IL-8 production of eosinophils incubated with heat-treated ESP was markedly increased comparable to that of cells treated with the lowest concentration used in this study. These findings suggest that the protease in the ESP of PwNEM pivotally regulates IL-8 production by controlling of eosinophil survival, depending on the amount of ESP released in vivo. Thus, the cysteine protease in the ESP of PwNEM could provide a novel role to control recruitment of inflammatory cells in larval-infected lesions in human paragonimiasis.