Echinococcus multilocularis: cell-mediated immune response in early and chronic alveolar murine hydatidosis

Expansion of Host Regulatory T Cells by Secreted Products of the Tapeworm Echinococcus multilocularis

Background

Alveolar echinococcosis (AE), caused by the metacestode larval stage of the fox-tapeworm Echinococcus multilocularis, is a chronic zoonosis associated with significant modulation of the host immune response. A role of regulatory T-cells (Treg) in generating an immunosuppressive environment around the metacestode during chronic disease has been reported, but the molecular mechanisms of Treg induction by E. multilocularis, particularly parasite immunoregulatory factors involved, remain elusive so far.

Methodology/Principal Findings

We herein demonstrate that excretory/secretory (E/S) products of the E. multilocularis metacestode promote the formation of Foxp3+ Treg from CD4+ T-cells in vitro in a TGF-β-dependent manner, given that this effect was abrogated by treatment with antibody to mammalian TGF-β. We also show that host T-cells secrete elevated levels of the immunosuppressive cytokine IL-10 in response to metacestode E/S products. Within the E/S fraction of the metacestode we identified an E. multilocularis activin A homolog (EmACT) that displays significant similarities to mammalian Transforming Growth Factor-β (TGF-β/activin subfamily members. EmACT obtained from heterologous expression failed to directly induce Treg expansion from naïve T cells but required addition of recombinant host TGF-β to promote CD4+ Foxp3+ Treg conversion in vitro. Furthermore, like in the case of metacestode E/S products, EmACT-treated CD4+ T-cells secreted higher levels of IL-10. These observations suggest a contribution of EmACT to in vitro expansion of Foxp3+ Treg by the E. multilocularis metacestode. Using infection experiments we show that intraperitoneally injected metacestode tissue expands host Foxp3+ Treg, confirming the expansion of this cell type in vivo during parasite establishment.

Conclusion/Significance

In conclusion, we herein demonstrate that E. multilocularis larvae secrete factors that induce the secretion of IL-10 by T-cells and contribute to the expansion of TGF-b-driven Foxp3+ Treg, a cell type that has been reported crucial for generating a tolerogenic environment to support parasite establishment and proliferation. Among the E/S factors of the parasite we identified a factor with structural and functional homologies to mammalian activin A which might play an important role in these activities.

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.

Animal model for the pathogenesis of reactive amyloidosis

The pathogenesis of amyloidosis is not well understood. Here, Zafer Ali-Khan, Weihua Li and Sic L. Chan present a metazoan parasite mouse model of reactive amyloidosis, review the relationship between chronic inflammation and multiorgan AA amyloidosis and postulate how ubiquitin might function in the processing of serum amyloid A and in AA amyloid formation in the endosomes-lysosomes of activated murine reticuloendothetial cells.

An experimental field approach to parasitism and immune defence in voles

The fox tapeworm Echinococcus multilocularis is typically perpetuated in a cycle with red foxes as definitive hosts and various rodent species as intermediate hosts. In this study, foxes were baited with a highly efficient drug against cestodes (praziquantel) in 5 blocks of 1 km2. Voles, Arvicola terrestris, the most abundant intermediate host species, were trapped in the 5 baited blocks and in 5 non-baited control blocks. Baiting the foxes reduced the prevalence of E. multilocularis in fox faecal samples in the baited blocks, but voles trapped in the two blocks did not differ in their infection rates. However, voles from the baited blocks had significantly smaller spleen masses and were more likely to be infested with mites than those from the control blocks, possibly reflecting different immunological activities. Our study suggests that the environmental contamination with E. multilocularis eggs, and perhaps those of other tapeworms, influences the immune system of the intermediate host species A. terrestris in the wild.

Immunohistochemical observations on cellular response in unilocular hydatid lesions and lymph nodes of cattle

As we believe the immunohistochemistry of the hydatid lesions and draining lymph nodes has never been studied, we collected them from the liver and lungs of cattle in Uruguay for such a study. Frozen sections of the tissues were immunohistochemically stained using monoclonal antibodies against surface markers CD2, CD4, CD5, CD8, B cell and granulocyte-monocyte/macrophage and antiserum against specific granules of bovine eosinophils. The adventitial layer of the cyst wall consists of a layer of epithelioid cells and connective tissue. The cells from the epithelioid cell layer were a kind of macrophage. In most cases having progressive hydatid cysts, CD8+ cells were predominant in the pericystic adventitia, and a relatively small number of CD4+ cells were in the same area. In the adventitial layer surrounding the regressive and involutional hydatid cysts, infiltrating lymphocytes were composed mostly of CD4+ cells. An eosinophil-mediated destruction of the laminated layer was recognized in the regressive and involuted hydatid cysts. The subpopulations of T cells in the local lymph nodes tended to be similar to T cells in the adventitial layer of hydatid lesions. From our findings, we consider that infiltration of eosinophils and the subpopulations of lymphocytes infiltrating the hydatid lesions in the liver and lungs are derived from cells in the draining lymph nodes of both organs.

The ambiguous role of immunity in echinococcosis: protection of the host or of the parasite?

In Echinococcus infection, at the metacestode stage, studies of the immune responses in the experimental murine model as well as in humans have shown that (1) cellular immunity induced by a Th1-type cytokine secretion was able to successfully kill the metacestode at the initial stages of development; (2) antigenic proteins and carbohydrates (and perhaps non-antigenic, mitogenic components) of the oncosphere/metacestode were able to interfere with antigen presentation and cell activation so that host lymphocytes and other immune cells could produce cytokines (especially IL-10) and other mediators able to inhibit the effector phase of cellular immune reaction; and (3) immunogenetic characteristics of the host were essential to this parasite-induced deviation of the immune response. In E. multilocularis infection, a combined Th1 and Th2 cytokine profile appears crucial for prolonged metacestode growth and survival. It may be hypothesized that Th1 cytokines promote the initial cell recruitment around the metacestode and are involved in the chronicity of the cell infiltrate leading to a fully organized periparasitic granuloma and its consequences, fibrosis and necrosis. The Th2 cytokines, on the other hand, could be responsible for the inhibition of a successful parasite killing especially because of the 'anti-inflammatory' potency of IL-10. This combination of various arms of the immune response results in a partial protection of both Echinococcus metacestode and host. However, it may also be considered responsible for several complications of the disease. The Th2-related IgE synthesis and mast cell activation, well known to be responsible for anaphylactic reactions in cystic echinococcosis, are more rarely involved in 'allergic' complications in alveolar echinococcosis (AE). However, the partial but chronic effects of the efficient Th1-related cellular immune response are responsible for cytotoxic events which both help metacestode growth and dissemination and lead to the central necrosis of the lesions and clinical complications of AE. Moreover, the Th-1 response is responsible for the major and irreversible fibrosis which leads to bile duct and vessel obstruction. In addition, the peri-parasitic fibrosis may be one of the reasons for the relative lack of efficacy of antiparasitic drugs. Modulation of the host immune response, by using Interferon alpha for instance, may be a new tool to generate an effective immune response against the parasite and to prevent AE and its complications.

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.

Secondary alveolar echinococcosis in lymphotoxin-alpha and tumour necrosis factor-alpha deficient mice: exacerbation of Echinococcus multilocularis larval growth is associated with cellular changes in the periparasitic granuloma

The availability of mice carrying a deletion of LT-alpha and tumour necrosis factor (TNF)-alpha genes enabled us to investigate the role of the TNF during alveolar echinococcosis. We compared the growth rate of Echinococcus multilocularis in LT-alphaTNF-alpha +/+ mice to that of mice having either no or only one LT-alphaTNF-alpha functionnal allele. LT-alphaTNF-alpha -/- mice harboured a significantly higher parasite burden than did the other two populations at 5, 10, and 15 weeks of infection, and they did not survive thereafter. Liver metacestodes removed from these mice were alive and the dehydrogenase activities of peritoneal metacestodes were decreased. Liver lesions regressed in most wild-type mice. Indeed, dead parasites were cordoned by granulomas containing numerous macrophages and lymphocytes leading to focal liver fibrosis at an early stage of infection. In contrast, most of LT-alphaTNF-alpha -/- mice harboured metacestodes interspersed with leucocytes, realising purulent abscesses with secondary extensive irregular fibrosis at a late stage of infection. Heterozygous mice had behavioural characteristics intermediate between homozygous mutants and wild-type mice. Levels of E. multilocularis-specific delayed-type hypersensitivity and serum antibodies were slightly decreased in LT-alphaTNF-alpha -/- mice. This study shows that TNF-alpha and/or LT-alpha genes play an essential role in the immune protection mechanisms against E. multilocularis at the site of infection.

In vivo treatment with recombinant IL-12 protects C57BL/6J mice against secondary alveolar echinococcosis

Using an experimental model of hepatic Echinococcus multilocularis infection in C57BL/6J mice, intraperitoneal administration of 0.8 microgram of recombinant IL-12 to mice with an established infection was shown to reduce the parasite burden as soon as two weeks after the end of treatment. At that time, in vitro Echinococcus multilocularis-induced spleen T cell proliferative responses as well as IFN-gamma and IL-5 production were higher in IL-12 treated mice than in untreated mice. Administration of 0.8 microgram of IL-12 at the time of infection was shown to be without effect on the parasite establishment. However, this treatment greatly inhibited the subsequent metacestode development. Indeed, ten weeks after infection, it induced a complete healing in 37.5% of mice. At that time, the development of metastases was inhibited in 68.75% of IL-12-treated mice. This reduction of parasite burden was mainly associated with a strong proliferation of spleen cells to E. multilocularis antigen and with a high IFN-gamma production. Altogether, our results show that IL-12 is of crucial importance in inhibiting the larval growth after the metacestode establishment in the liver and suggest that this cytokine could be of potential value in the treatment of human alveolar echinococcosis.

Characterization of T-cell immune responses of Echinococcus multilocularis-infected C57BL/6J mice

Specific and non-specific parasite-induced changes in lymphocyte responses were analysed in C57/BL/6J mice after intrahepatic infection with Echinococcus multilocularis. Spleen cells harvested at selected times after infection were in vitro stimulated with mitogens or a crude soluble parasite extract (EmAg) at an optimized dose. Cell proliferative responses to Con-A were not modified by the infection over the first 22 weeks. In contrast, LPS-induced responses were decreased from the 13th week. A strong CD4+ proliferative T-cell response to the parasitic extract of infected mouse spleen cells was observed at the early stage of infection. This response then progressively decreased but remained significantly higher than that of control mice until the 19th week of infection. Cytokine production was investigated after in vitro EmAg stimulation of spleen cells. IFN-gamma, IL-2, IL-5 were produced within the first weeks after infection whereas the detection of IL-10 was slightly delayed. Thus, the promotion of the disease does not appear associated with the expansion of one rather than another T-cell subset in C57BL/6J mice. A general immunosuppression affecting both mitogenic and parasite-specific T-cell responses was observed at the end of the infection.

Interleukin-5 is the predominant cytokine produced by peripheral blood mononuclear cells in alveolar echinococcosis

An involvement of cellular immunity in alveolar echinococcosis is strongly suggested by the intense granulomatous infiltrations observed around the hepatic parasite lesions. However, the basis of cellular immunoregulation in patient with alveolar echinococcosis is poorly understood. The present report shows a comparative analysis of lymphoid cell function in peripheral blood mononuclear cells (PBMC) of 16 patients with alveolar echinococcosis and of healthy individuals. Our in vitro restimulation studies with crude Echinococcus multilocularis antigen demonstrated that PBMC from patients with alveolar echinococcosis were responsive to challenge with parasitic antigen as measured by lymphoid cell proliferation. In this system, we also evaluated cytokine expression at the gene and protein levels after stimulation with E. multilocularis antigen. Analysis of cytokine mRNA expression revealed distinct patterns of cytokine expression in patients and normal donors. By using reverse transcriptase PCR, we could demonstrate that the TH1 cytokine transcripts interleukin-2 (IL-2) and gamma interferon (IFN-gamma) are present in PBMC from patients with alveolar echinococcosis. Moreover, it was found that stimulation with E. multilocularis antigen induced or enhanced the expression of the TH2 cytokine IL-3, IL-4, IL-10, and especially IL-5 mRNAs in PBMC from 13 of 16 patients with alveolar echinococcosis. Two patients who were examined after radical surgery, as well as another patient with a stable course of the disease under continuous chemotherapy, were not able to generate the same pattern of cytokine response and had no evidence of IL-5 mRNA synthesis. In contrast to the frequent expression of TH2 cytokine mRNAs observed in patients with alveolar echinococcosis, PBMC cultures from normal donors showed prominent IL-2 and IFN-gamma mRNA expression but weak IL-3, IL-4, and IL-10 mRNA expression. Most interestingly, IL-5 mRNA was substantially absent in PBMC from healthy individuals. In accordance with the mRNA studies, it was found that E. multilocularis antigen induced the secretion of large amounts of IL-5 and intermediate amounts of IFN-gamma in patients with alveolar echinococcosis, whereas large amounts of IFN-gamma and no or threshold amounts of IL-5 were detected in supernatants from healthy individuals. Collectively, the present study provides the first evidence that a TH2 immune response is gradually activated during the course of E. multilocularis infection, indicating a critical role for IL-5 in the manifestation of human alveolar echinococcosis.

Echinococcus multilocularis: in vitro interactions between protoscolices and Kupffer cells

Echinococcus multilocularis protoscolices collected from experimentally infected jirds were incubated for 2 weeks in rat hepatic cell cultures cocultivated with or without feeder cells (BALB/c 3T3 and IAR 20). Scanning and transmission electron microscopy studies were performed during the course of the culture period. Kupffer cells (Kc) were seen adhering to the anterior and posterior ends of the protoscolices. Some protoscolices were fixed to the cell monolayer by a cluster of Kc adhering to the posterior end of the parasite. These cells were phagocytosing the glycocalyx and the electron-dense distal end of the microthrix of the protoscolex tegument. An alteration in the superficial tegumental cytoplasm with extensive mitochondrial damage was also noted. The properties expressed by Kc against protoscolices in vitro might also be relevant for proliferation of metacestodes in vivo.

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

The interaction between protoscoleces of Echinococcus multilocularis and activated murine macrophages was examined in this study. Marked protoscolicidal activity was displayed by peritoneal macrophages (PM) activated with interferon-gamma (IFN-gamma), or IFN-gamma plus lipopolysaccharide. Pretreatment of the parasites with heat-inactivated specific murine infection serum, but not with normal serum rendered them more susceptible to PM killing. NG-monomethyl-L-arginine, a competitive inhibitor of L-arginine completely inhibited the killing activity of activated PM, while reconstitution of arginine-free medium with L-arginine restored the killing properties of the activated PM. The results show that activated PM have the ability to kill E. multilocularis protoscoleces in vitro and suggest that reactive nitrogen intermediates (RNI) play an important role in the mechanism. An oxygen-mediated mechanism did not appear to play a role because scavengers of reactive oxygen species did not reduce the killing activity. The arginine-dependent killing mechanism was enhanced by superoxide dismutase (SOD), probably because SOD might prolong the effect of nitric oxide. Secretion of RNI by activated macrophages may be capable of a significant role in preventing of the dissemination of E. multilocularis infection in vivo.

Suppression of T-cell proliferation by CD8+ T cells induced in the presence of protoscolices of Echinococcus multilocularis in vitro

Immunoregulatory influences of protoscolices (PSC) of Echinococcus multilocularis on murine T-lymphocyte functions have been examined in an in vitro system. Proliferative responses of spleen cells stimulated with concanavalin A (ConA) or anti-CD3 monoclonal antibodies were depressed by the addition of PSC. In the presence of PSC, both interleukin-2 (IL-2) production and IL-2 receptor (IL-2R) expression by lymphocytes stimulated with ConA were significantly reduced. However, exogenous IL-2 reconstituted both the ConA-stimulated proliferative responses and IL-2R expression. These findings suggest that PSC of E. multilocularis can suppress lymphoid cell responses via influences on IL-2 production. Indeed, addition of CD(8+)-enriched cells from cultures stimulated with ConA plus PSC to fresh spleen cells showed marked suppression of the ConA responses. IL-2 production as well as IL-2R expression on the spleen cells so treated were suppressed. These findings reveal a suppressive immunologic function induced by E. multilocularis PSC that involves inhibition of IL-2 production and reduction of IL-2R expression. The PSC-induced CD8+ cells appear to play a key role in the suppressive regulation of host immune responses against E. multilocularis.

Secondary Echinococcus multilocularis infection in severe combined immunodeficient (scid) mice: biphasic growth of the larval cyst mass

E. multilocularis infection was suppressed in C.B-17 mice after intraperitoneal inoculation of protoscoleces, with larval cysts weighing no more than 1.0 g. In scid mice, which are genetically identical to C.B-17 except for a deficiency in functional lymphocytes, infection progressed and larval cysts reached a mass of 17.5 g at 15 weeks post-infection. The growth of the larval cyst mass in scid mice was similar to that in other susceptible mouse strains, with a biphasic pattern. Histological observations revealed giant cells and granulomatous inflammation in the C.B-17, but not in the scid mice. These results led to the conclusion that suppression of the growth of the larval cyst mass in the initial stage of infection in susceptible mice strains is caused by factors other than the host's lymphocytic immune response.

Cellular immunity in experimental Echinococcus multilocularis infection. I. Sequential and comparative study of specific in vivo delayed-type hypersensitivity against E. multilocularis antigens in resistant and sensitive mice

Species- or strain-related differences in receptivity of intermediate hosts to E. multilocularis larvae could be related to differences in specific cellular immune response of the host. In order to test this hypothesis, we assessed the delayed-type hypersensitivity (DTH) to E. multilocularis antigens (EmAg) in mice of three strains differing by their sensitivity (AKR and C57BL.6) or resistance (C57BL.10) to E. multilocularis infection. DTH was determined by measuring in vivo the foot-pad response 24 h after an EmAg antigenic challenge. The level of positive response was evaluated in immunized mice; however, a typical DTH response was only observed by immunizing mice with a strong adjuvant schedule. Course of DTH in the immunized mice was shown to be somewhat different in sensitive and resistant mice. The differences were much more marked in mice infected with proliferative E. multilocularis larvae. The levels of the footpad response was significantly higher in resistant mice, although the peak of the reaction was obtained later than in sensitive mice. DTH, expressed by the foot-pad response against EmAg, remained significant for the entire period of observation in sensitive as well as in resistant mice. There was no correlation between receptivity of the murine hosts and levels of specific antibodies against EmAg. These results suggest a relationship between resistance to E. multilocularis infection and intensity and/or course of DTH in mice. The resistance could be mediated by some particularities of the in situ cellular immune response in the periparasitic granuloma.

Immunology and molecular biology of Echinococcus infections

Echinococcus spp. are the etiological agents of hydatid disease in man and other intermediate hosts. Many questions regarding the factors which determine susceptibility/resistance to hydatid disease, and the factors which influence the viability and fertility of hydatid cysts, remain to be answered. Recent research into the effects of hydatid infection on the immune system of the host has provided some insights into the host-parasite relationships. Immunochemical and recombinant DNA techniques are being applied to improve diagnosis of hydatidosis in man and E. granulosus infection in dogs, and also in the development of vaccines against infection with taeniid cestode larvae. The successes which have been achieved in these areas are likely to provide valuable tools for the control of cystic hydatidosis in man. These recent studies in the areas of immunobiology, serological diagnosis and vaccination are reviewed.

Echinococcus multilocularis: inhibition of murine neutrophil and macrophage chemotaxis

Resident peritoneal neutrophils and macrophages from mice infected with 50 +/- 5 cysts of Echinococcus multilocularis were collected at 2, 4, 6, 8, 10, and 16 weeks postinfection. Their ability to respond and migrate to purified parasite larval antigens or endotoxin-activated mouse serum (EAMS) in comparison to normal peritoneal cells from uninfected mice was tested in vitro using Boyden chambers. Early in the infection, both cell types responded to the specific and nonspecific chemoattractants as the control group. However, at 8 and 10 weeks postinfection, the neutrophils and macrophages lost their response to parasite antigens but retained their ability to migrate to EAMS. Toward the 12th and 16th week postinfection, both cell types lost their ability to migrate to the specific as well as the nonspecific factors. The data presented suggest that the cellular mechanisms of recognition and chemotaxis in mice infected with alveolar hydatid cysts are impaired.

Echinococcus multilocularis: relationship between persistent inflammation, serum amyloid A protein response and amyloidosis in four mouse strains

LPS-hyporesponsive (C3H/HeJ) and LPS-sensitive (C57BL/6, CBA/J, C3H/HeSn) strains of mice were infected intraperitoneally with 50 alveolar hydatid cysts (AHC) to assess the effect of protracted severe inflammation on serum amyloid A protein (SAA) concentrations, splenic amyloid deposition, and pre- and postamyloidotic alterations in the splenic architecture. In general, the SAA concentrations in all the four mouse strains showed a moderate but steady increase throughout the course of infection. Splenic amyloid deposition commenced between 6 to 8 weeks postinfection (p.i.) when the SAA concentrations were relatively low and increased progressively until 12 weeks p.i. when 52 to 78% of the splenic parenchyma was obliterated. CBA mice which harbored the largest AHC throughout the 12-week course of infection showed the poorest SAA and amyloid responses; the situation was reversed in the C3H/HeSn strain. Histologically, most of the splenic follicles, during the stage of maximum amyloid deposition, appeared hypocellular. Their T-cell-dependent periarterial sinuses were either totally depleted of cells or contained plasma cells or myeloid cells. These results show that (a) there is no direct correlation between the intensity of inflammation, SAA concentrations, or amounts of amyloid deposition in either of the four mouse strains and (b) amyloidosis secondary to AHC infection differs from other experimental mouse models of amyloidosis in the magnitude of SAA elevation during the preamyloid phase.

Echinococcus multilocularis: the non-specific binding of different species of immunoglobulins to alveolar hydatid cysts grown in vivo and in vitro

Alveolar hydatid cysts (AHC) were isolated from C57BL/6J and BALB/c mice at 8 and 12 weeks post-infection from subcutaneous and intraperitoneal foci and cultured in vitro. Freshly isolated as well as in vitro-grown cysts were incubated with Fc or F(ab')2 fragments of human, rabbit, mouse, goat or sheep immunoglobulins, then washed and incubated with a fluorescein-conjugated rabbit or goat F(ab')2 fraction of antisera to each of the above primary sera. Significant fluorescence on the surface of AHC was detected when they were incubated with human, rabbit or mouse Fc fractions followed by the addition of goat or rabbit fluorescein-conjugated antiserum. No fluorescence was detected when the AHC were incubated with the F(ab')2 fragments and fluorescein-conjugated antiserum, except when the primary antiserum was mouse F(ab')2 fractions. Cysts grown in vitro retained their binding ability to human, rabbit or mouse Fc fractions. However, the intensity of fluorescence decreased proportionally with time. The maximum intensity of staining was observed with small cysts. Large cysts showed diminished fluorescence. The non-specific binding of human, mouse or rabbit immunoglobulins (Fc fractions) to AHC was also confirmed by rosetting with sheep erythrocytes (SRBC) which suggests that the larvae of Echinococcus multilocularis may utilize the presence of Fc receptors on their surface in order to elude immune destruction by the host.

Characterization of amyloid protein from mice infected with alveolar hydatid cyst: isolation, purification, and amino acid composition

The physicochemical properties of alveolar hydatid cyst-induced amyloid (AHCA) were investigated. The AHCA was extracted from spleens, livers, and kidneys of C57BL/6J mice at 12 weeks postinfection and purified on Sephadex G-100 and G-50 gel columns. By using SDS-PAGE and isoelectric focusing techniques the purified AHCA protein showed a molecular weight (MW) of approximately 8,700 and a pI value of 5.3, respectively. The azocasein-induced AA amyloid from C57BL/6J mice had a similar MW but a pI value of 5.8. Unlike mouse AA amyloid, the AHCA was resistant to KMnO4-trypsin treatment, and was shown to cross-react with antisera raised against mouse AA amyloid. The immunologic cross-reactivity between mouse AA, serum amyloid A protein, and AHCA as determined by immunoperoxidase, indirect immunofluorescence, and gel diffusion tests indicated antigenic similarity between AHCA and mouse AA. The amino acid composition of purified AHCA presented both similarities and differences when compared with published data from mouse AA and spontaneously developed mouse amyloid proteins. We report here for the first time the presence of small amounts of methylated basic amino acids and amino sugars in AHCA protein.

Echinococcus granulosus: in vitro effect of monensin on the tegument of the protoscolex

Protoscoleces of Echinococcus granulosus were incubated in a 10 microM solution of monensin and their viability and the ultrastructure of their tegument were monitored over a 36 h period. The earliest effects of the ionophore, apparent within 15 min, involved a degree of cisternal swelling of the tegumentary Golgi complexes. Swelling became more pronounced with time and cytons eventually contained numerous large electron-lucent vesicles. Residual bodies indicative of autophagy were observed in the cytons and distal cytoplasm from 1 h onwards. All movement of protoscoleces ceased after 1 h and the surface of the soma subsequently became folded, possibly suggesting spastic paralysis. Later, vacuoles and large cytoplasmic blebs were observed in the distal cytoplasm and viability dropped rapidly after 12 h. All protoscoleces were dead at 36 h. The potential of monensin as an in vivo protoscolicidal agent is discussed.

Echinococcus granulosus: changes in the transformational behaviour of murine lymph node cells during early infection

Subcutaneous inoculation of living Echinococcus granulosus protoscolices (PSC) caused blastic transformation in local lymph node cells (LNC). The effect was maximal seven days post-infection (p.i.), had declined by day 21, and was prevented by killing the PSC prior to inoculation. LNC from inoculated mice also showed marked enhancement of blastogenesis in response to a secondary stimulation by live PSC in vitro. This secondary reaction occurred after exposure to living or killed PSC. There was generally enhanced reactivity to T- and B-cell mitogens at day 7. Phytohaemagglutinin was exceptional in that the killed parasite caused early changes in reactivity as above, but the live parasite induced a rise at 56 days p.i. It is concluded that E. granulosus may cause a determinate change in T-cell function.

Echinococcus multilocularis: responses to infection in Mongolian gerbils

Mongolian gerbils (Meriones unguiculatus) inoculated intraperitoneally with three acephalic cysts of Echinococcus multilocularis were very susceptible to infection. Aspects of the responses of gerbils to this infection were examined to determine if they could be related to the progress of the infection. Hematologic changes observed during the infection included anemia, reticulocytosis, lymphocytopenia, neutrophilia, monocytosis, and eosinopenia; these changes were related to the size of the infection. Infected gerbils also produced specific protein-A binding antibodies to E. multilocularis. At 14 weeks after inoculation, infected gerbils showed splenomegaly and somewhat elevated serum transaminase levels, although serum 5'-nucleotidase levels were normal.

The immune response to Echinococcus granulosus: sequential histological observations of lymphoreticular and connective tissues during early murine infection

This paper describes the organ weight changes and the early (0 to 56 days) histological and ultrastructural changes in the lymphoid structures and injection sites after subcutaneous infection of Balb/c mice with Echinococcus granulosus protoscolices (psc). Local lymph nodes enlarged markedly, reaching maximal weight 5 to 14 days after infection (pi). Expansion of the thymus-dependent areas of draining lymph nodes was first recognized at 3 days pi and reached a maximum between 14 and 21 days pi. Lymphoproliferation within B-cell-dependent areas was less extensive and of shorter duration. Comparable, but diminished, changes were seen in contralateral lymph nodes and spleen. Lymphoid cell depletion was observed in T-dependent areas of lymphoid organs by 56 days pi. Local inflammatory reactions to psc, at the site of injection, were intense, involving neutrophils, eosinophils, macrophages and mast cells. Viable psc were present until at least 6 weeks pi. The central role of the T-lymphocyte in recognition of, and response, to E. granulosus psc is discussed.

Experimental alveolar echinococcosis. Suitability of a murine model of intrahepatic infection by Echinococcus multilocularis for immunological studies

An experimental model of human alveolar echinococcosis was developed, using intrahepatic injection of E. multilocularis larvae in mice differing by their sensitivity to this parasite; it seems to be suitable for studying the relationship between cell-mediated immunity and a) growth of the parasite, b) development of fibrosis.

Humoral and cellular immunity in patients with hepatic alveolar echinococcosis. A 2 year follow-up with and without flubendazole treatment

Parameters of humoral and cellular immunity were assessed in 12 patients with alveolar echinococcosis (AE) of the liver before, during and after discontinuation of treatment with flubendazole (FZ). In infected patients, before any medical treatment values of serum IgG, IgA, total haemolytic complement and C4 were significantly higher than those observed in control subjects; IgA levels were higher in jaundiced patients. Specific antibodies assayed by indirect haemagglutination and immunoelectrophoresis were present only in infected patients and were shown to decrease by the sixth month of treatment; however, similar fluctuations were observed without treatment. The percentage and absolute number of B lymphocytes, and total circulating lymphocytes, were significantly lower in patients with AE. An impairment of functional activity of T cells assayed by the leucocyte migration test, with PPD and Candidin as antigens, was demonstrated despite a normal percentage of SRBC rosettes. The 'score' of migration index still decreased during FZ treatment and returned to initial values after the year of follow-up without treatment. These results suggest that human AE is associated with important immunological disturbances. Changes in humoral immunity can be unequivocally considered to be a consequence of the parasite infection. The primary or secondary nature of the impairment of cellular immune responses and its mechanisms remain to be elucidated. Flubendazole could be responsible for an increase of cellular immune alterations in these patients.

Cystolytic events and the possible role of germinal cells in metastasis in chronic alveolar hydatidosis

Two and six week old alveolar cysts of Echinococcus multilocularis were isolated from C57BL/6J and Balb/cJ mice and used to study the cystolytic events mediated by resident inflammatory cells. Ultramicroscopic degenerative changes in these cysts were compared with the ultrastructure of in vitro grown cysts (free of inflammatory cells). Macrophages, eosinophils and neutrophils were found to bind to the laminated layer of plasma membrane of the germinal layer of cysts. Hydrolytic enzymes and eosinophil granules released extracellularly from inflammatory cells at the cyst surface appear to dissolve the laminated layer and produce gaps in the plasma membrane. Macrophages actively phagocytose the granular ground substance of the disintegrated laminated layer. Cystolysis results in the release of germinal cells which measure 6-17 microns, possess nuclei with prominent nucleoli, sparse endoplasmic reticulum, Golgi complexes and oval mitochondria. Based on histologic evidence we believe that germinal cells may be the progenitors of cysts. The possibility that germinal cells may give rise to distant metastatic foci of alveolar cysts, in immunocompromised hosts, is discussed.

Growth of Echinococcus multilocularis in gerbils exposed to different environmental temperature

Gerbils kept at high (35 degrees C) temperature harbored a significantly larger Echinococcus multilocularis cyst biomass than those kept at room (21 degrees C) and low (5 degrees C) temperature. Parasite induced adrenomegaly was observed in all temperature groups.

Pathogenesis and host response in subcutaneous alveolar hydatidosis. I. Histogenesis of alveolar cyst and a qualitative analysis of the inflammatory infiltrates

C57L/J male mice were infected subcutaneously in their left flank with 10 cysts of Echinococcus multilocularis. The dimensions and histologic features of the larval cyst mass (LCM) were determined at three days, at weekly intervals for 12 weeks, and at 22 weeks postinfection. The LCM doubled its size between 3 and 12 weeks, and at 22 weeks it was five times larger than at three weeks. During the proliferative phase, the LCM was infiltrated massively by neutrophils, macrophages, and progenitors of the plasma cell series. The first two cell types were found firmly bound to the laminated layer of both intact and degenerating cysts, whereas plasma cells colonized the fibrohistocytic corona and the interlacunar stroma harboring individual cysts. By 22 weeks, the proliferation of the cysts had ceased and histologically the LCM consisted of fibrous and fibrohistiocytic stroma, thick-walled fertile and sterile brood capsules, and predominantly plasmacytic and histiocytic infiltrates. In addition to exogenous budding evidence has been presented also suggesting the role of free germinal cells in the histogenesis of LCM. Regulation of cyst proliferation in susceptible hosts is discussed with reference to antibody-dependent cell mediated cytotoxicity with nonlymphoid inflammatory cells.

Pathogenesis and host response in subcutaneous alveolar hydatidosis. II. Intense plasmacellular infiltration in the paracortex of draining lymph nodes

Male C57L/J mice were infected subcutaneously in the left flank with 10 cysts of Echinococcus multilocularis. The draining and contralateral nodes were excised at weekly intervals, weighed, and examined histologically. Lymphoproliferation occurred in both the follicles and the paracortex (PCA) of the draining lymph nodes at one week postinfection (p.i.). Disorganization in the PCA of the draining nodes, was characterized by replacement of lymphocytes by plasma cells and the flattening of the endothelial cells lining the postcapillary venules. This began at three weeks p.i. and was completed by 12 weeks p.i. No comparable alterations occurred in the contralateral nodes during this period, but at 22 weeks p.i. these nodes were disorganized and histologically identical to the draining nodes. The growth and histogenesis of the subcutaneous alveolar cysts correlated with the expansion and disorganization of the PCA. The regulation of subcutaneous murine alveolar hydatidosis is discussed with reference to immune-deviation which is brought about by the antigenic load and plasmacellular infiltration in the draining lymph nodes.

Humoral response to sheep red blood cells in C57L/J mice during early and chronic stages of infection with Echinococcus multilocularis cysts

C57L/J male mice infected with Echinococcus multilocularis cysts were challenged intraperitoneally at 4, 8, and 12 weeks postinfection (p.i.) with 3 x 10(9) sheep erythrocytes. The direct plaque forming cells, 2-mercaptoethanol (2-ME) sensitive (4-day sera) and 2-ME-resistant (8-day sera) haemagglutinin responses were significantly elevated at eight and 12 weeks p.i. as compared to controls or the fourweeks postinfected mice. Possible mechanisms of immunopotentiation in the chronically infected mice is discussed in relation to the larval cyst mass, splenomegaly, and B cell hyperplasia in the lymphoid tissues during the course of infection.

Pathological changes in the lymphoreticular tissues of Swiss mice infected with Echinococcus granulosus cysts

Swiss mice infected intraperitoneally with approximately 1,500 protoscolices of Echinococcus granulosus and sacrificed at three and 13 months post infection yielded both viable and degenerated hydatid cysts. The mean cyst weights in the three and 13 months post infected mice were 0.13 and 2.1 g, respectively. Sections of spleens and lymph nodes in the three months post infected mice showed hyperplastic follicles and blastoid cells in thymus dependent areas. At 13 months post infection T cells from paracortex and periarterial areas were replaced by plasma cells and confluent sheets of histiocytes; follicles had retained germinal centres and medullary areas showed intense plasmacytosis and sinus histiocytosis. Failure of mice to control the histogenesis of hydatid cyst with reference to numerical reduction in T cells is discussed.