Arginine-dependent generation of reactive nitrogen intermediates is instrumental in the in vitro killing of protoscoleces of Echinococcus multilocularis by activated macrophages

Regulatory T cells in lung disease and transplantation

Pulmonary disease can refer to the disease of the lung itself or the pulmonary manifestations of systemic diseases, which are often connected to the malfunction of the immune system. Regulatory T (Treg) cells have been shown to be important in maintaining immune homeostasis and preventing inflammatory damage, including lung diseases. Given the increasing amount of evidence linking Treg cells to various pulmonary conditions, Treg cells might serve as a therapeutic strategy for the treatment of lung diseases and potentially promote lung transplant tolerance. The most potent and well-defined Treg cells are Foxp3-expressing CD4+ Treg cells, which contribute to the prevention of autoimmune lung diseases and the promotion of lung transplant rejection. The protective mechanisms of Treg cells in lung disease and transplantation involve multiple immune suppression mechanisms. This review summarizes the development, phenotype and function of CD4+Foxp3+ Treg cells. Then, we focus on the therapeutic potential of Treg cells in preventing lung disease and limiting lung transplant rejection. Furthermore, we discussed the possibility of Treg cell utilization in clinical applications. This will provide an overview of current research advances in Treg cells and their relevant application in clinics.

The effects of Zataria multiflora aromatic water and nano emulsion of Z. multiflora essential oil on the serum level of IFN-γ and IL-4 in mice with hydatidosis

The aim of the present investigation was to evaluate the impacts of Zataria multiflora aromatic water (ZMAW) and nano emulsion (NE) of Z. multiflora essential oil (ZMEO) on IL-4 (Th2-derived cytokine) and IFN-γ (Th1-derived cytokine) concentrations in mice with hydatidosis. Sixty four healthy BALB/c female mice were intraperitoneally injected by 1500 live protoscoleces of Echinococcus granulosus. Five month after injection, the infected mice were divided into seven treatment groups, including: Albendazole (100 mg/kg), ZMAW (100 ml/L), Albendazole 100 + ZMAW (Albendazole 100 mg/kg and ZMAW 100 ml/L), Albendazole 50 + ZMAW (Albendazole 50 mg/kg and ZMAW 100 ml/L), Albendazole 100 + NE of ZMEO (Albendazole 100 mg/kg and NE of ZMEO 10 ml/L), albendazole 50 + NE of ZMEO (albendazole 50 mg/kg and NE of ZMEO 10 ml/L) and the control group with no treatment. The mice received the ZMAW, NE of ZMEO and/or albendazole through drinking water for 90 days. At the end of treatment (90 days), blood specimens were harvested from all mice. A significant reduction in IL-4 concentration was revealed in the albendazole 50 group + NE of ZMEO, when compared to the control group (P < 0.05). No significant difference was noticed for the IFN-γ concentration between the trial groups. Increased IFN-γ: IL-4 ratio was observed in the albendazole 50 + ZMAW, Albendazole 50 + NE of ZMEO, Albendazole 100 + NE of ZMEO groups in comparison with the control group (P < 0.05). The findings observed in the current study showed that the administration of ZMAW and NE of ZMEO along with albendazole could enhance the IFN-γ: IL-4 ratio (Th1/Th2 balance), which may have therapeutic value in the treatment of hydatid disease.

The Effects of Nitric Oxide and Inhibitor, and Combination of Albendazole and Praziquantel On Liver in Mice Injected with Echinococcus granulosus Larvae

In this study, the role of nitric oxide (NO) in the pathogenesis of hydatidosis and the interaction with effects of anthelmintic drugs, albendazole and praziquantel, were examined in larval infection caused by protoscolices obtained from hydatid cysts of sheep liver in Albino Balb/c mice. Animals were divided into ten groups including controls and infected groups. Larval infection was established with intraperitoneal injection of protoscolices. Eight months after infection with protoscolices, the infected animals were divided into 6 groups. The infected animals were given a selective inhibitor of inducible nitric oxide synthase (iNOS) L-N⁶-(1-Iminoethyl) lysine-hydrochloride (L-NIL), NO donor sodium nitroprusside (SNP), albendazole and praziquantel as anthelmintic drugs for 7 days. In addition, control groups were composed of intact group, control, anthelmintic drugs + L-NIL, and anthelmintic drugs + SNP. The liver and blood samples were taken for cytological, histological, immunohistochemical and biochemical analyses 7 days after treatments at the end of experiment. The animals injected with protoscolices showed histopathological changes including inflammation areas, infiltration and accumulation of leukocytes, dilation of sinusoids, and damage in endothelial cells and hepatocytes at light microscopy. Electron microscopy were revealed severe damage in sinusoidal endothelial cells, leukocytes especially eosinophils in sinusoid lumens and disorganization in endoplasmic reticulum and nuclear membrane. Endothelial nitric oxide synthase (eNOS) and iNOS reactions were increased in the tissue. Anthelmintic drugs decreased inflammation areas and damages; however, it did not change NOS reactions in the animals given protoscolices. L-NIL and SNP diminished both iNOS and eNOS reactions. Unlike the group administered the inhibitor, SNP treated group exhibited less inflammation areas. Combination of these substances and drugs resulted in decreased inflammation areas. eNOS and iNOS reactions decreased in the drugs and SNP administered group, while only iNOS reaction was decreased in L-NIL given infection group. In addition, the infected groups which received SNP displayed expanded sinusoids and hepatocytes with vacuoles, intriguingly. While levels of serum nitrite/nitrate elevated only in the infection group given drugs and SNP, it decreased in the L-NIL administered group. Tissue level of malondialdehyde increased in infection groups with drugs and SNP. In conclusion, the results indicated that NO plays an important role in the pathogenesis of hydatidosis.

Dual Role of Hepatic Macrophages in the Establishment of the Echinococcus multilocularis Metacestode in Mice

Echinococcus multilocularis larvae, predominantly located in the liver, cause a tumor-like parasitic disease, alveolar echinococcosis (AE), that is characterized by increased infiltration of various immune cells, including macrophages, around the lesion that produces an "immunosuppressive" microenvironment, favoring its persistent infection. However, the role of hepatic macrophages in the host defense against E. multilocularis infection remains poorly defined. Using human liver tissues from patients with AE and a hepatic experimental mouse model of E. multilocularis, we investigated the phenotype and function of hepatic macrophages during the parasite infection. In the present study, we found that a large number of CD68⁺ macrophages accumulated around the metacestode lesion in the liver of human AE samples and that both S100A9⁺ proinflammatory (M1 phenotype) and CD163⁺ anti-inflammatory (M2 phenotype) macrophages were significantly higher in close liver tissue (CLT) than in distant liver tissue (DLT), whereas M2 macrophages represent the dominant macrophage population. Furthermore, E. multilocularis-infected mice exhibited a massive increase in macrophage (F4/80⁺) infiltration in the liver as early as day 5, and the infiltrated macrophages were mainly monocyte-derived macrophages (CD11b^hi F4/80^int MoMFs) that preferentially differentiated into the M1 phenotype (iNOS⁺) at the early stage of E. multilocularis infection and then polarized to anti-inflammatory macrophages of the M2 phenotype (CD206⁺) at the chronic stage of infection. We further showed that elimination of macrophages by treatment of mice with clodronate-liposomes before E. multilocularis infection impaired worm expulsion and was accompanied by a reduction in liver fibrosis, yielding a high parasite burden. These results suggest that hepatic macrophages may play a dual role in the establishment and development of E. multilocularis metacestodes in which early larvae clearance is promoted by M1 macrophages while persistent metacestode infection is favored by M2 macrophages.

Effects of Allium sativum on IFN-γ and IL4 concentrations in mice with cystic echinococcosis

The aim of the current investigation was to assess the impacts of methanolic extract of Allium sativum (MEAS) on IL-4 (a cytokine derived from Th2 cells) and IFN-ɣ (a cytokine derived from Th1 cells) levels in mice infected with Echinococcus granulosus. Sixty healthy BALB/c female mice were used in this study. Each animal was intraperitoneally injected with 1500 protoscoleces. The infected animals were randomly divided into six groups: albendazole (100 mg/kg), MEAS 10 (10 mg/kg), MEAS 20 (20 mg/kg), MEAS 40 (40 mg/kg), MEAS 80 (80 mg/kg) and control group with no treatment. The studied animals received albendazole and/or MEAS through drinking water for 30 days. Serum IFN-γ concentration significantly increased in the MEAS 20 and 80 groups in comparison to the control, albendazole and MEAS 10 groups (P < 0.05). The serum IL-4 level showed no significant difference between the trial groups. The findings of this study showed that MEAS at 20 and 80 mg/kg concentrations enhanced Th1 cell response in mice with cystic echinococcosis.

Albendazole increases the inflammatory response and the amount of Em2-positive small particles of Echinococcus multilocularis (spems) in human hepatic alveolar echinococcosis lesions

Background

Alveolar echinococcosis (AE) is caused by the metacestode stage of Echinococcus multilocularis. The inflammatory response to this infection is influenced by the interaction of the parasite with the host. We aimed to analyze human liver lesions infected with Echinococcus multilocularis and the changes of the cellular infiltrates during albendazole (ABZ) treatment.

Methodology/Principal findings

We analyzed liver tissue samples from 8 untreated patients, 5 patients treated with two daily doses of 400 mg ABZ for up to two months and 7 patients treated for more than two months with the same ABZ therapy. A broad panel of monoclonal antibodies was used to characterize the lesion by immunohistochemistry. A change in the cellular infiltrate was observed between the different chemotherapy times. During the initial phases of treatment an increase in CD15⁺ granulocytes and CD68⁺ histocytes as well as in small particles of Echinococcus multilocularis (spems) was observed in the tissue surrounding the metacestode. Furthermore, we observed an increase in CD4⁺ T cells, CD20⁺ B cells and CD38⁺ plasma cells during a longer duration of treatment.

Conclusions/Significance

ABZ treatment of AE leads to morphological changes characterized by an initial, predominantly acute, inflammatory response which is gradually replaced by a response of the adaptive immune system.

Alveolar echinococcosis (AE) is a life-threatening disease in humans caused by the larval stages of E. multilocularis. It has been shown that the infection in humans is associated with a modulated immune response. Depending on multiple factors, such as the stage of disease, total or partial surgical resection and albendazole (ABZ) therapy are treatments of choice. ABZ is known as a parasitostatic drug that has to be administered for years to suppress metacestode development. Here we compared human liver lesions before and after short and long term treatment with ABZ by immunohistochemistry using a broad panel of antibodies. We found a change in the cellular infiltrate, characterized by a shift to an infiltrate rich in T cells, B cells and plasma cells during long-term treatment with ABZ, including a pronounced detection of small particles of E. multilocularis (spems). We argue that ABZ treatment is likely to change the cellular infiltrate, leading to an enhancement of the host immune response during treatment.

Molecular cloning and characterization of cystatin, a cysteine protease inhibitor, from Angiostrongylus cantonensis

Cystatins are thiol proteinase inhibitors ubiquitously present in mammalian body and serve various important physiological functions. In the present study, a novel cystatin molecule (AcCystatin) was cloned from a cDNA library of Angiostrongylus cantonensis fourth-stage larvae. The putative 14-kDa protein contained 120 residues with cystatin-conserved motifs known to interact with the active site of cysteine peptidases and showed high identities with cystatins from other nematodes. RT-PCR analysis revealed that the expression pattern of AcCystatin was equal at the time points of third-stage larvae, fourth-stage larvae, and adults of the parasite life cycle. The recombinant AcCystatin (rAcCystatin) expressed and purified from Escherichia coli has been demonstrated to possess an obvious inhibitory activity against cathepsin B and could significantly upregulate nitric oxide production from IFN-gamma activated RAW 264.7 macrophages. Sera from mice (non-permissive host) infected with A. cantonensis detected rAcCystatin by Western blot, while the sera from infected rats (permissive host) could not. The results implied that AcCystatin might be an immunoregulator in A. cantonensis infection.

Nitric oxide and respiratory helminthic diseases

Nitric oxide (NO) is a very simple molecule that displays very important functions both in helminths (mainly those involved in respiratory pathology) and in mammalian hosts. In this paper we review four issues related to interaction of NO and lung helminthic diseases. Firstly, we evaluated data available on the NO synthesis and release by helminths and their biological role. Next, we summarized the effect of antigens obtained from different phases of the biological cycle on NO production by host mammalian cells (mainly from human sources). Thirdly, we revised the evaluation of NO on the biological activities and/or the viability of respiratory helminths. Lastly, the deleterious consequences of increased production of NO during helminthic human infection are detailed.

Similarity and diversity in macrophage activation by nematodes, trematodes, and cestodes

This review summarizes current knowledge of macrophages in helminth infections, with a focus not only on delineating the striking similarities in macrophage phenotype between diverse infections but also on highlighting the differences. Findings from many different labs illustrate that macrophages in helminth infection can act as anti-parasite effectors but can also act as powerful immune suppressors. The specific role for their alternative (Th2-mediated) activation in helminth killing or expulsion versus immune regulation remains to be determined. Meanwhile, the rapid growth in knowledge of alternatively activated macrophages will require an even more expansive view of their potential functions to include repair of host tissue and regulation of host metabolism.

In Vitro Study of Nitric Oxide Metabolites Effects on Human Hydatid of Echinococcus granulosus

Hydatidosis is characterized by the long-term coexistence of larva Echinococcus granulosus and its host without effective rejection. Previous studies demonstrated nitric oxide (NO) production (in vivo and in vitro) during hydatidosis. In this study, we investigated the direct in vitro effects of NO species: nitrite (NO₂⁻), nitrate (NO₃⁻) and peroxynitrite (ONOO⁻) on protoscolices (PSCs) viability and hydatid cyst layers integrity for 24 hours and 48 hours. Our results showed protoscolicidal activity of NO₂⁻ and ONOO⁻ 24 hours and 3 hours after treatment with 320 μM and 80 μM respectively. Degenerative effects were observed on germinal and laminated layers. The comparison of the in vitro effects of NO species on the PSCs viability indicated that ONOO⁻ is more cytotoxic than NO₂⁻. In contrast, NO₃⁻ has no effect. These results suggest possible involvement of NO₂⁻ and ONOO⁻ in antihydatic action and point the efficacy of these metabolites as scolicidal agents.

14-3-3 proteins in Echinococcus: their role and potential as protective antigens

14-3-3 Proteins are a family of highly conserved proteins among all eukaryotic organisms studied so far. As basically intracellular proteins, they play a key role in basic cellular events related to cellular proliferation, including signal transduction, cell-cycle control, cell differentiation and cell survival. The 14-3-3 proteins have been described and characterized in several parasites, and mostly studied in Echinococcus granulosus and Echinococcus multilocularis. Here, we review the discoveries regarding this protein family in the genus Echinococcus, describing new data about specific aspects related with their implication in the parasite biology and immunology in the frame of the host-parasite relationship.

Taeniid history, natural selection and antigenic diversity: evolutionary theory meets helminthology

Large sets of nucleotide sequence data of parasitic helminths have been accumulated in the past two decades. Our ability to improve the health of people and animals using this knowledge has not increased proportionally, however. Evolutionary biology provides the background to understand how parasites adapt to their hosts, and computational molecular biology offers the tools to infer the mechanisms involved. The study of antigenic diversity, a way for parasites to overcome host defenses against parasites, has been neglected in helminths, yet such a study could contribute to the development of more efficient drugs, diagnostic tests and vaccines. This review focuses on the study of adaptive evolution as the cause of antigenic diversity in tapeworms and its potential applications.

Research on targeting sources of alveolar echinococcosis in Japan

Echinococcus multilocularis is a fatal zoonotic parasite in the Northern Hemisphere. Recently, it has become endemic in many countries in Asia, especially in the northern island of Hokkaido in Japan. The increasing threat of public health due to alveolar echinococcosis has compelled researches for sensitive diagnosis and effective control. This paper reviews on the epidemiology, diagnosis and control of echinococcosis specifically in Japan. International collaborative responses by researchers and government initiatives such as mandatory reporting system for veterinarians who diagnose echinococcosis in dogs are presented. Successful control measures in Japan using anthelmintic fortified baits for foxes are described. Assessment of prevalence rates during control campaigns is analyzed favoring the use of intravital diagnosis rather than the traditional necropsy method from hunting or trapping activities of wild foxes. The novel concept of "endogenous development" by local resident volunteers towards sustainable control of echinococcosis is stressed.

Echinococcus multilocularis laminated-layer components and the E14t 14-3-3 recombinant protein decrease NO production by activated rat macrophages in vitro

Echinococcus multilocularis and Echinococcus granulosus cause alveolar and cystic (unilocular) echinococcosis, respectively, in humans and animals. It is known that these parasites can affect, among other molecules, nitric oxide (NO) production by periparasitic host cells. Nevertheless, detailed dissection of parasite components specifically affecting cell NO production has not been done to date. We compare the effect of E. granulosus and E. multilocularis defined metacestode structural (laminated-layer associated) and metabolic (14-3-3 protein, potentially related with E. multilocularis metacestode tumor-like growth) components on the NO production by rat alveolar macrophages in vitro. Our results showed that none of these antigens could stimulate macrophage NO production in vitro. However, a reversed effect of some Echinococcus antigens on NO in vitro production was found when cells were previously exposed to LPS stimulation. This inhibitory effect was found when E. multilocularis laminated-layer (LL) or cyst wall (CW) soluble components from both species were used. Pre-stimulation of cells with LPS also resulted in a strong, dose-dependent reduction of NO and iNOS mRNA production after incubation of cells with the E14t protein. Thus, the E. multilocularis 14-3-3 protein appears to be one of the components accounting for the suppressive effect of the CW and LL metacestode extracts.

Enhanced inducible nitric oxide synthase expression and nitrotyrosine accumulation in experimental granulomatous hepatitis caused by Toxocara canis in mice

The involvement of inducible nitric oxide synthase (iNOS) and nitrotyrosine (NT) in pathogenesis of toxocaral granulomatous hepatitis (TGH) in a murine host was quantitatively determined by biochemical, parasitological, pathological, and immunohistochemical assessments in a 42-week investigation. Mice were sacrificed for serum collection and histological processing as well as acid-pepsin digestion of the liver in a larval recovery study. Significantly increased levels of total serum NO were found in the trial, indirectly suggesting iNOS activation in the liver. iNOS reactivity was predominantly observed in infiltrating leucocytes in lesions and normal and apocrine-like cholangiocytes; in contrast, hepatocytes and multinucleated giant cells showed negative cytoplasmic staining in TGH. Strong iNOS-like reactivity was also detected on the body wall of larvae. The locations of NT reactivity were nearly identical to those of iNOS expression; infiltrating leucocytes or cholangiocytes stained for iNOS were also stained for NT in TGH. Enhanced iNOS expression, but not invading larvae (r = 0.256, P = 0.211), seemed to play a certain role in pathological damage in TGH due to a significant correlation between iNOS expression and serum alanine aminotransferase (ALT) levels (r =0.593, P = 0.021) in the trial. Our present results indicate a potential therapeutic strategy for treatment of GH caused by other nematodes through manipulation of iNOS expression.

Poorer NF-κB signaling by microfilariae in macrophages from BALB/c mice affects their ability to produce cytotoxic levels of nitric oxide to kill microfilariae

Upon activation with microfilariae (mf), macrophages from C57Bl/6 mice showed higher nuclear factor-kappa B (NF-kappa B) but lower activating protein 1 DNA-binding activity as compared to BALB/c macrophages. The C57Bl/6 macrophages produced cytotoxic levels of nitric oxide (NO) to kill Setaria cervi mf as compared to BALB/c macrophages. Inhibition of the NF-kappa B signal by pyrrolidine dithiocarbamate (PDTC) blocked NO production and microfilaricidal activity of C57Bl/6 macrophages and inclusion of the exogenous NO generator (SNP) in the PDTC treated C57Bl/6 macrophage cultures induced mf cytotoxicity. These results underscore that the NF-kappa B signal (induced in response to mf) is important for the NO-mediated microfilaricidal activity of macrophages.

Cytokine response and outcome of infection depends on the infective dose of parasites in experimental infection by Echinococcus granulosus

We here analysed whether the cytokine responses in early and late experimental infection with Echinococcus granulosus depend on the dose of parasites to which the host is exposed. To this purpose Balb/c mice were inoculated intraperitoneally (i.p.) with either 500 or 2000 protoscoleces. Splenocytes of mice were obtained at days 3, 7, 14 and 21 and also on week 37 post-infection and cultured in vitro with protoscolex antigens. Type-1 and type-2 cytokines were analysed in supernatants by ELISA. Results showed that the inoculation of 500 protoscoleces induced an early type-0 and a late type-2 cytokine response, whereas the inoculation of 2000 protoscoleces induced an early type-2 and a late type-0 cytokine response. Parasite growth was lower in the group inoculated with the low infective dose. These results indicate that the cytokine response during the infection by the helminth E. granulosus depends on the dose of parasites to which the host has been exposed.

Inducible nitric oxide synthase deficiency in mice increases resistance to chronic infection with Echinococcus multilocularis

The production of nitric oxide (NO) by intraperitoneal macrophages of mice during secondary infection with Echinococcus multilocularis mediates immunosuppression at early and late stages of infection. We addressed the role of NO in host resistance against this extracellular metazoan parasite by infecting inducible nitric oxide synthase knockout ((iNOS-KO) mice (of the C57BL/6 background) with 100 metacestode vesicles. The parasite weight was significantly lower in iNOS-KO mice when compared with wild-type (WT) mice at 4 months postinfection (late stage), thus demonstrating that iNOS deficiency confers a certain degree of resistance against persistent chronic infection. However, histological analysis of periparasitic tissue showed no differences between WT and iNOS-KO mice, as both exhibited granuloma formation and the presence of giant cells. Together with histology, the production of a high level of interferon-gamma (IFN-gamma) in infected iNOS-KO mice upon stimulation with concanavalin A (Con A) and VF-antigen indicated normal T-cell signalling in these animals. As expected, peritoneal exudate cells (PEC) from infected iNOS-KO mice produced no detectable NO, while the PEC from infected WT mice produced high levels of NO after stimulation with lipopolysaccharide (LPS) and parasite protein or carbohydrate antigen, or even without in vitro stimulation. Consequently, the high level of NO production observed during chronic infection in WT mice appears to contribute more to immunosuppression than to limitation of parasite growth. This is also reflected by the fact that splenocyte proliferation was significantly higher and parasite masses lower in iNOS-KO mice (at 1 and 4 months postinfection) than in WT mice.

Concepts in immunology and diagnosis of hydatid disease

Echinococcosis is a cosmopolitan zoonosis caused by adult or larval stages of cestodes belonging to the genus Echinococcus (family Taeniidae). The two major species of medical and public health importance are Echinococcus granulosus and E. multilocularis, which cause cystic echinococcosis (CE) and alveolar echinococcosis (AE), respectively. Both CE and AE are both serious diseases, the latter especially so, with a high fatality rate and poor prognosis if managed inappropriately. This review discusses new concepts and approaches in the immunology and diagnosis of CE, but comparative reference has also been made to AE infection and to earlier pivotal studies of both diseases. The review considers immunity to infection in the intermediate and definitive hosts, innate resistance, evasion of the immune system, and vaccination of intermediate and definitive hosts, and it particularly emphasizes procedures for diagnosis of CE and AE, including the value of immunodiagnostic approaches. There is also discussion of the new advances in recombinant and related DNA technologies, especially application of PCR, that are providing powerful tools in the fields of vaccinology and molecular diagnosis of echinococcosis.

Toxocara canis antigens stimulate the production of nitric oxide and prostaglandin E2 by rat alveolar macrophages

The effect of four Toxocara canis antigens on nitric oxide (NO) and prostaglandin E2 (PGE2) synthesis was studied in vitro using rat alveolar macrophages. Somatic and excretory/secretory T. canis antigens prepared from adult worms and LII larvae were incubated with rat alveolar macrophages obtained by bronchoalveolar lavage at concentrations of 0.1-50 microg/ml. Both excretory/secretory adult antigen (ESA) and somatic LII antigen (SLII) stimulate the release of nitrites by alveolar macrophages. This effect was specific (inhibited by L-NAME and L-canavanine) and dose-dependent; 30 microg and 10 microg being the most effective concentrations of ESA and SLII, respectively. Western blot and reverse transcriptase-polymerase chain reaction analyses revealed that ESA antigen stimulates the production of NO at transcriptional level. T. canis ESA also stimulated macrophages to produce PGE2 at transcriptional level. The addition of L-canavanine decreased the release of PGE2 significantly, which suggests that NO mediates the production of this prostaglandin. These results indicate that T. canis can stimulate the release of vasodilatory mediators by macrophages of the host.

In-vitro susceptibility of hydatid cysts of Echinococcus granulosus to nitric oxide and the effect of the laminated layer on nitric oxide production

Murine hydatid cysts of Echinococcus granulosus were incubated in vitro in the presence of nitric oxide produced from S-nitroso-N-acetylpenicillamine (SNAP) or interferon-gamma activated peritoneal macrophages. In both situations, evidence of cyst damage and death was observed by microscopy in over 77% of cysts after 3 days, indicating that intact hydatid cysts could be susceptible to a Th1 driven macrophage attack. A crude extract of the laminated layer from cysts was found to be able to reduce the production of nitric oxide from activated macrophages in vitro and in vivo and this may have been due to phagocytosis of laminated layer fragments by the macrophages. The results indicate that, although cysts may be susceptible to the effects of nitric oxide, the laminated layer may be involved in downregulating nitric oxide production.

Course of Brugia malayi infection in C57BL/6J NOS2 +/+ and -/- mice

Previous results from our laboratory using pharmacological approaches suggested a role for nitric oxide (NO) in the host defense against the human filarial parasite, Brugia malayi. We sought to determine whether a complementary genetic approach, using mice homozygous for a targeted mutation in the gene encoding inducible nitric oxide-synthase (NOS2), would confirm our observation. We hypothesized that such mice would exhibit some deficit in their ability to clear B. malayi. Our data show that the course of infection in NOS2-/- mice is the same as in wild-type mice. Thus, peritoneal cellular responses to infection are similar in NOS2-/- and wild-type mice, with the exception that T cells form a higher percentage of total peritoneal cells in the former. We find virtually no serum IgE in NOS2-/- mice, suggesting a less robust Th2 response. In contrast, NOS2-/- mice demonstrate an early rise in IgG2a titers compared to B6 +/+ mice. Our data suggest that NO is not an obligate requirement for the elimination of B. malayi from the peritoneal cavities of mice.

Oestrus ovis (Diptera: Oestridae): effects of larval excretory/secretory products on nitric oxide production by murine RAW 264.7 macrophages

Larvae of Oestrus ovis (Insecta: Diptera: Oestridae) are common parasites of nasal and sinus cavities of sheep and goats. Previous studies revealed that crude extracts of larvae modify NO synthesis by ovine monocyte derived macrophages. The aim of this study was to investigate the larval excretory/secretory products effects on nitric oxide production by murine tumour macrophages RAW 264.7. Stimulation of RAW macrophages by excretory/secretory products of the three instars larvae (25 microg/ml) significantly increased nitrite concentrations in culture supernatants compared to negative and positive Escherichia coli lipopolysaccharide control. This effect was time and dose dependent. Nitrite production in culture supernatants was due to induction of isoform NOS-2 because both NG monomethyl L-arginine (100 microM) and dexamethasone (20 microM) inhibited, by 60 and 50%, respectively, nitrite accumulation in culture supernatants. First steps of purification, by ion exchange chromatography, indicated that one protein of 29 kDa was able to induce NO synthesis by macrophages. Further studies are needed for a better characterization of these molecule and to investigate their immunogenicity for a vaccine approach.

Cytokine gene expression in peripheral blood mononuclear cells (PBMC) from patients with pharmacologically treated cystic echinococcosis

The influence of pharmacological treatment on the immune response of patients with Echinococcus granulosus infection was evaluated by reverse transcriptase-polymerase chain reaction (RT-PCR) to determine mRNA expression for IL-12 p35, IL-12 p40, interferon-gamma (IFN-gamma), tumour necrosis factor-alpha (TNF-alpha) and IL-4 in PBMC from 12 patients before and after chemotherapy and from seven uninfected controls. Most patients' PBMC showed measurable amounts of IL-12 p35, IL-4, IFN-gamma and TNF-alpha mRNA in parasite antigen-stimulated and unstimulated cultures. Conversely, IL-12 p40 mRNA was detected almost exclusively in successfully treated patients (86%) after therapy. In these patients semiquantitative analysis of RT-PCR products showed a significant difference between IL-12 p40 mRNA mean levels before and after therapy (P = 0.03 in parasite antigen-stimulated cultures; P = 0.001 in unstimulated cultures). IL-4 mRNA was weakly expressed before therapy and more highly so after treatment in both groups of patients and under both culture conditions; IL-4 mRNA reached its highest level in post-therapy PBMC from patients in whom therapy failed (stimulated cultures). IFN-gamma and TNF-alpha mRNA expression increased in patients who responded to therapy and decreased in patients who did not. In contrast to IL-12 p35, IFN-gamma and TNF-alpha mRNAs, IL-12 p40 and IL-4 mRNAs were detected exclusively in patients, suggesting a close relationship between these two cytokines and cystic echinococcosis. Our findings indicate that chemotherapy influences the immune response, thus determining changes in Th1/Th2 cytokine mRNA patterns, predominantly in IL-12 p40 and IL-4 mRNA expression.

Effects of Anisakis simplex on nitric oxide production in J774 macrophages

Since nitric oxide (NO) was recognized as a potent microbicidal agent, its role in host defence against intracellular parasites has been widely demonstrated. Recent evidence suggests a role for NO in combating extracellular and multicellular pathogens. This defence activity has been demonstrated toward the larvae of Schistosoma mansoni, microfilariae of Onchocerca linealis, several stages of Brugia malayi and protoscoleces of Echinococcus multilocularis. Many parasites suppress Th1 lymphocytes and directly inhibit NO production by inducing cytokines, such as IL-4, IL-10 and TGF-beta. In this study, we have investigated the effects of Anisakis simplex, an enhancer of Th2-dominant responses, on NO production. We studied the effect of crude extracts (CE) and excretory-secretory (ES) products on the induction of inducible nitric oxide synthase (iNOS) in bacterial lipopolysaccharide (LPS)-treated J774 macrophages. Stimulation of macrophages by LPS (1 microg/ml) increased nitrite concentrations in the culture medium at 24 h. Co-administration of A. simplex products with LPS, dose-dependently reduced the accumulation of nitrite. Nitrite production is due to induction of iNOS, and both L-NAME (N(G)-nitro-L-arginine methyl ester) (50 microM) and dexamethasone (10 microM) inhibited nitrite accumulation (54.2 and 92.1% inhibition, respectively). The inhibition of nitrite production by A. simplex was 42.1-97.8% in the range 4.75-76 microg/well (CE products) and 37.2-61.5% in the range 5-20 microg/well (ES products). Cell viability assayed by the mitochondrial-dependent reduction of MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) verified that the inhibition was not due to general cellular toxicity. However, the effects of A. simplex, were reduced when NOS had been induced by prior exposure to LPS and any possible further induction was blocked by cycloheximide, an inhibitor of protein synthesis.

Nitric oxide-mediated immunosuppression following murine Echinococcus multilocularis infection

In some parasitic infections immunosuppression is a prominent characteristic of the host-parasite interplay. We have used a murine alveolar echinococcosis (AE) model in susceptible C57BL/6 mice to document a suppressed splenocyte proliferative response to concanavalin A (Con A) at the early (1-month) stage and to Echinococcus multilocularis-crude antigen (Emc-antigen) at the late (4-6-month) stage of chronic infection. Despite proliferative suppression, splenic cytokine production [interleukin-2 (IL-2), IL-4 and interferon-gamma (IFN-gamma)] in response to Con A or Emc-antigen stimulation was not suppressed at 1 month postinfection (p.i.). Infection resulted in a strong Mac-1+ cell infiltration of the peritoneal cavity and spleen. Peritoneal cells (PEC) from mice infected at the 1-month stage were rich in macrophages and expressed significantly higher levels of transcripts for the inflammatory cytokine IL-1beta and for tumour necrosis factor-alpha and inducible nitric oxide synthase (iNOS), when compared with PEC from non-infected control mice. Conversely, the IL-10 transcript level remained low and did not change during infection. Spleen cells supplemented with PEC from infected mice induced a marked increase in the levels of nitrite in response to Con A and Emc-antigen stimulation, and also a complete suppression of splenic proliferation. The spleen cells from late-stage infected mice expressed only background levels of IL-10 but greatly increased levels of iNOS, when compared with normal spleen cells. This observation correlated with the immunosuppression demonstrated at the late stage of murine AE. Furthermore, the suppressed splenic proliferative responses observed at the early and late stage were reversed to a large extent by the addition of NG-monomethyl-l-arginine and partially by anti-IFN-gamma. Thus, our results demonstrated that the immunosuppression observed in chronic AE was not primarily dependent on IL-10 but rather on nitric oxide production by macrophages from infected animals.

T-cell activity associated with secondary infections and implanted cysts of Echinococcus granulosus in BALB/c mice

Selected cytokine profiles of lymphocytes were assessed in BALB/c mice infected with protoscoleces of Echinococcus granulosus. Late stages of the infection (three months+) were characterized by more dominant Th2 activity with elevated IL-4 and IL-10 and reduced IFN-gamma output by Con-A and antigen stimulated splenocytes. Circumparasitic leucocytes produced mainly IL-10 by five months post infection. A peak in IFN-gamma production in the first month of infection may suggest Th1 or Th0 activity at this time and this may be correlated with initial protoscolex death. In addition, cytokine profiles from mice implanted with intact hydatid cysts were also assessed. At two weeks post implantation all cysts were still viable and cytokine production was characterized mainly by elevated IL-10 production. However, at four months post implantation, some of the cysts from two mice had been killed whilst all cysts in the remaining mouse remained viable. In the mice where dead cysts were present, elevated levels of IFN-gamma were detected from splenocytes and circumparasitic cells. Elevated IL-4 was also evident with the splenocytes. In the mouse with viable cysts IFN-gamma production was reduced Results indicate that IFN-gamma(Th1) activity may be correlated with killing of both protoscoleces and established cysts of E. granulosus.

Role of nitric oxide in host defense against an extracellular, metazoan parasite, Brugia malayi

The mechanisms by which mammalian hosts eliminate microparasites such as bacteria and viruses are well established. In viral infections, these mechanisms include the interferons, neutralizing and opsonizing antibodies, and cytotoxic T lymphocytes. In bacterial infections, polymorphonuclear leukocytes and macrophages, often facilitated by opsonizing antibodies, ingest the infectious agent and mediate host defense. In addition, complement, in the presence of specific antibodies directed against surface antigens, can lyse certain bacterial pathogens. In contrast, our understanding of the host defenses against metazoan, extracellular parasites is less well grounded. We obtained data by two different approaches to document the role of nitric oxide (NO) as a mediator of host defense against a human nematode parasite. First, treatment of immunocompetent, nonpermissive mice with an inhibitor of NO synthase abrogated resistance to Brugia malayi, one of the causative agents of human lymphatic filariasis. Second, treatment of permissive, immunodeficient mice with a compound that releases NO conferred resistance to infection. These data reinforce studies by James and her coworkers (I. P. Oswald, T. A. Wynn, A. Sher, and S. L. James, Comp. Biochem. Physiol. Pharmacol. Toxicol. Endocrinol. 108:11-18, 1994) on the role of NO in defense against trematode parasites and of Kanazawa et al. (T. Kanazawa, H. Asahi, H. Hata; K. Machida, N. Kagei, and M. J. Stadecker, Parasite Immunol. 15: 619-623, 1993) on cestode parasites.

Protective immune mechanisms against the metacestode of Echinococcus multilocularis

Infection with the larval stage of the fox tapeworm Echinococcus multilocularis results in a life-threatening hepatic disease concerning humans and intermediate rodent hosts. Immunoepidemiological surveys provided information that a large proportion of infected individuals may demonstrate either constitutional resistance to early post-oncospheral development of the parasite or late resistance to disease by exhibiting an intrahepatic died-out parasite lesion. Similar events have been found in secondary infections of laboratory rodents. Dissection of humoral and cell-mediated immune responses in susceptible versus resistant individuals provides insight into immunological pathways associated with the different outcome of infection. Survival strategy of the metacestode obviously focuses on the crucial role played by the parasite laminated layer. This layer protects the metacestode from host effector mechanisms which can potentially kill the proliferating germinative compartments in case of resistant hosts. Bruno Gottstein and Richard Felleisen here discuss the need to search for more parameters discriminating between the different immune pathways in order to find out (immunogenetic?) predispositions responsible for the respective phenomena.