Activation of RIG-I signaling in the early stage of Paragonimus proliferus infection causes lung injury via type I immune response in rat

Paragonimiasis is a common zoonotic parasitic disease. The retinoic acid-inducible gene I (RIG-I) signaling is very important for the host to recognize invading pathogens (especially viruses and bacteria). However, the role of RIG-I signaling in the early stages of P. proliferus infection remains unclear. Therefore, in this study, Sprague-Dawley (SD) rat models with lung damage caused by P. proliferus were established. Experimental methods including Enzyme-linked Immuno Sorbent Assay (ELISA), real-time fluorescent quantitative polymerase chain reaction (PCR), western blotting, and hematoxylin and eosin (HE) staining were used to explore the mechanisms of lung injury caused by P. proliferus. As a result, the expression of the mRNA and proteins of RIG-I signal-related key target molecules, including RIG-I, tumor necrosis factor (TNF) receptor associated factor 6 (TRAF6), interferon regulatory Factor 7 (IRF7), IPS-1, and downstream C-X-C chemokine ligand 10 (CXCL10), were significantly up-regulated immediately after infection, peaked at 3 or 7 days, and showed a downward trend on after 14 days. The levels of pro-inflammatory cytokines interleukin-1 (IL-1), interferon (IFN)-α, -β, and -γ, which represent type 1 immune response, gradually increased and reached a peak by 14 days, which was consistent with the changes in the degree of inflammatory damage observed under HE staining of lung tissues. In conclusion, RIG-I signaling is activated in the early stage (before 14 days) of P. proliferus infection, it is inferred that the lung injury of the host may be related to the activation of RIG-I like signaling to induce type I immune response.

Effects of L-type Ca2+ channel antagonists on in vitro excystment of Paragonimus ohirai metacercariae induced by sodium cholate

The inhibitory effects of L-type Ca2+ channel antagonists on Na cholate-induced in vitro excystment (CIIE) of Paragonimus ohirai metacercariae were studied. At concentrations of 10 microM, nicardipine and nimodipine inhibited CIIE completely and by approximately 92%, respectively. Nitrendipine and (+/-)-verapamil inhibited CIIE by about one half and one third, respectively. Nifedipine and diltiazem did not inhibit CIIE significantly. At higher concentrations, nitrendipine at 20 microM completely inhibited CIIE, and (+/-)-verapamil at 40 microM inhibited CIIE by 93%. Nifedipine and diltiazem inhibited CIIE only slightly and little, respectively, even at 40 microM. Complete inhibition by nicardipine at 10 microM required preincubation of metacercariae with the antagonist for 15 min. The inhibitory effects of nicardipine and nimodipine were reversible, and most of the nimodipine-treated metacercariae could excyst within 1 h after being washed, but the nicardipine-treated ones started to excyst 1 h after washing. Nicardipine suppressed the active movement of encysted juveniles evoked by Na cholate, whereas nimodipine did not suppress this significantly. These results suggested that L-type Ca2+ channels appeared to be involved in CIIE of P. ohirai metacercariae and that the inhibitory effect of the channels was due primarily to factors other than the inhibition of muscular activity, probably involving the secretion and release of enzymes lytic against the metacercarial cyst wall.

Excretory-Secretory Products Secreted by Paragonimus westermani Delay the Spontaneous Cell Death of Human Eosinophils through Autocrine Production of GM-CSF

BACKGROUND

Eosinophils play important roles in tissue inflammatory responses associated with helminth infections. Excretory-secretory products (ESP) produced by tissue-invasive helminths contain a large quantity of proteolytic enzymes that can modulate the host's immune responses. However, little is known regarding the roles of worm-derived products that are responsible for eosinophilic inflammatory responses in helminth infections.

OBJECTIVE

In the present study, we investigated whether ESP produced by Paragonimus westermani, which cause pulmonary or extrapulmonary paragonimiasis in human beings, regulates both cell survival and death of human eosinophils.

METHODS

The ESP was obtained from P. westermani newly excysted metacercariae (PwNEM). Eosinophils were purified from peripheral blood of healthy donors, and the purified eosinophils were incubated with or without the ESP secreted by PwNEM. The viability of eosinophils was assessed by staining with propidium iodide using the flow cytometer.

RESULTS

When eosinophils were incubated with a low concentration of the ESP produced by PwNEM, which totally consists of proteolytic enzymes, eosinophil cell death was delayed compared with results for cells incubated with medium alone. In fact, the ESP at a low concentration stimulated eosinophils to produce detectable levels of GM-CSF that can delay eosinophil cell death. In contrast, eosinophil cell death was dose-dependently accelerated when cells were incubated with high concentrations of the ESP. To see whether the dose-dependent biphasic survival effect of the ESP on eosinophils is primarily due to the protease activity contained in the ESP, a high dose of the ESP was treated with heat at 56 degrees C for 30 min before being added to eosinophils. Attenuating protease activity in a high dose of the ESP by heat treatment reversed the ESP-afforded eosinophil cell death. This prolonged survival of eosinophils induced by the heated ESP was remarkably inhibited by anti-GM-CSF-neutralizing mAb and Jak2 kinase inhibitor AG-490.

CONCLUSION

These results suggest that the proteases in the ESP secreted by PwNEM are able to regulate eosinophil survival through the autocrine production of GM-CSF. Thus, the enhanced eosinophil survival induced by Paragonimus-secreted products may contribute to the elicitation of eosinophilic inflammatory responses at the worm-infected lesion in human paragonimiasis.

Paragonimus westermani: molecular cloning, expression, and characterization of a recombinant yolk ferritin

Ferritin is an intracellular protein involved in iron metabolism. A cDNA PwYF-1 cloned from the adult Paragonimus westermani cDNA library encoded a putative polypeptide of 216 amino acids homologous with ferritins of vertebrates and invertebrates. Febinding motifs identified in PwYF-1 polypeptide were conserved and predicted to form a ferroxidase center. PwYF-1 polypeptide contained an extended peptide of 45 amino acids at its C-terminus. Recombinant PwYF-1 protein, expressed and purified from Escherichia coli, showed iron-uptake ability and ferroxidase activity. Ferroxidase activity of recombinant PwYF-1 protein was reactivated by secondary addition of apotransferrin to assay mixture. Mouse immune serum raised against the recombinant PwYF-1 protein recognized specifically 24 kDa protein from adult P. westermani lysate. PwYF-1 protein was localized to vitelline follicles and the eggs of P. westermani. Collectively, PwYF-1 protein was identified as a P. westermani yolk ferritin.

Excretory-secretory product of Paragonimus westermani newly excysted metacercariae inhibits superoxide production of granulocytes stimulated with IgG

It is well known that the cysteine proteases in excretory-secretory product (ESP) of Paragonimus westermani newly excysted metacercariae (PwNEM) are capable of degrading IgG in vitro. Recent evidence suggests that the IgG-coated surface, such as found on parasites, is one of the most effective physiologic stimuli for granulocyte activation. Therefore, this study was designed to investigate the effect of excretory-secretory product (ESP) of PwNEM on superoxide production of granulocytes stimulated with IgG. The 96-well plates were coated with human IgG (0, 10, 30, 100 micrograms/ml) in the absence or presence of ESP. When granulocytes were incubated in the wells coated with human IgG in the presence of ESP, the level of superoxide production of granulocytes was reduced to about 90% when compared to the cells incubated in the wells coated with IgG alone. This inhibitory effect of the ESP on IgG-induced superoxide production of granulocytes was concentration-dependent. These results suggest that ESP secreted by PwNEM may be important in the control of effector functions of granulocytes stimulated with IgG in human paragonimiasis.

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

Eosinophils are important effector cells in host defense against parasites. Excretory-secretory product (ESP) produced by helminthic worms plays important roles in the uptake of nutrients, migration in the host tissue, and in immune modulation. However, little is known about the ability of the ESP to directly trigger eosinophil apoptosis. This study investigated whether the ESP of newly excysted metacercariae of Paragonimus westermani could induce apoptosis in human eosinophils. Apoptosis was assayed by staining the cells with FITC-annexin V, and the cells were analyzed by flow cytometry. It was found that the ESP of newly excysted metacercariae of P. westermani induced a direct time- and concentration-dependent increase in the rate of constitutive apoptosis in mature human eosinophils. Eosinophil apoptosis was first apparent 3 hr after treatment with the ESP and continued to increase after 6 hr of incubation with respect to the cells cultured in the absence of the ESP. While only 2.8% of the eosinophils incubated in the medium for 3 hr were apoptotic, 7.6%, 10.9% and 22.6% of the eosinophils treated with 10, 30 and 100 micrograms/ml ESP were apoptotic, respectively. This result suggests that the ESP of newly excysted metacercariae of P. westermani directly induce eosinophil apoptosis, which may be important for the survival of the parasites and the reduction of eosinophilic inflammation in vivo.

Two types of parenchymal cells in the lung fluke Paragonimus ohirai (Digenea: Troglotrematidae) characterized by the cytochemistry of their mitochondria

Morphology and respiratory function were studied in situ and in the isolated mitochondria of Paragonimus ohirai. Two types of parenchymal cells (i.e., Pc1 and Pc2 cells), whose mitochondria differ in terms of morphology and staining for cytochrome c oxidase activity, were found in fluke tissues. Enzymatic and spectrophotometric analyses of the isolated mitochondria showed that fluke mitochondria possess both aerobic and anaerobic respiratory chains. These results suggest that there are two mitochondrial populations in fluke parenchymal cells, one possessing an aerobic respiratory chain and the other an anaerobic respiratory chain.

Respiratory chain of the lung fluke Paragonimus westermani: facultative anaerobic mitochondria

The respiratory chain of adult Paragonimus westermani, a lung fluke, was characterized in isolated mitochondria. The fluke mitochondria exhibited cyanide- and antimycin A-sensitive succinate oxidase activity at a rate of 16.8 nmol O2 min-1 mg-1 protein. The succinate oxidation was shown to be stimulated by ADP and linked to the formation of membrane potential. The specific activities of oxidoreductases composing the succinate oxidase system, i.e., succinate-ubiquinone and succinate--cytochrome c oxidoreductase (complex II and complex II-III, respectively) and cytochrome c oxidase (complex IV), were compared in mitochondria from adult Paragonimus, bovine heart (an aerobic tissue), and muscle of adult Ascaris suum which possesses an anaerobic respiratory chain. The activity values of complex II-III and complex IV were high, middle, and low for bovine heart, Paragonimus, and A. suum, respectively, whereas the activity of complex II was comparable among the three sources. The cytochrome contents of Paragonimus mitochondria as determined by difference absorption spectrophotometry ranged between those in Ascaris and bovine mitochondria for types c and aa3 cytochromes. Paragonimus mitochondria exhibited a high activity of NADH-fumarate reductase; the specific activity was about 18-fold higher in fluke submitochondria than in bovine heart submitochondria. Quinone analysis by HPLC and mass spectrometry showed that the fluke mitochondria contain both rhodoquinone-10 and ubiquinone-10 at concentrations of 0.572 and 0.321 nmol mg-1 mitochondrial protein, respectively. These data clearly show that mitochondria from adult P. westermani, unlike adult Ascaris mitochondria, possess both cyanide-sensitive succinate oxidase and NADH-fumarate reductase systems, indicating that the fluke mitochondria are facultatively anaerobic.

[Antigenic localities in the tissues of the young adult worm of Paragonimus westermani using immunogold labeling method]

In order to observe the antigenic localization in the tissues of the young adult Paragonimus westermani, immunogold labeling method was applied using serum immunoglobulins(IgG) of the dog which infected with isolated metacercariae from Cambaroides similis. The sectioned worm tissue was embedded in Lowicryl HM 20 medium and stained with infected serum IgG and protein A gold complex (particle size; 12 nm). It was observed by electron microscopy at each tissues of the worm. The gold particles were not observed on the basal lamina of the tegument, interstitial matrix of the parenchyma, the muscle tissue and mitochondria of the tegument. The gold particles were specifically labeled in the secretory granules in the vitelline cells. They were predominantly labeling on the epithelial lamela and lumen of caecum. The above finding showed that antigenic materials in young adult worm tissue were specifically concentrated on the tegumental syncytium as well as cytoplasm of tegumental cells.