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

Urotensin II and urantide exert opposite effects on the cellular components of atherosclerotic plaque in hypercholesterolemic rabbits

Increasing levels of plasma urotensin II (UII) are positively associated with atherosclerosis. In this study we investigated the role of macrophage-secreted UII in atherosclerosis progression, and evaluated the therapeutic value of urantide, a potent competitive UII receptor antagonist, in atherosclerosis treatment. Macrophage-specific human UII-transgenic rabbits and their nontransgenic littermates were fed a high cholesterol diet for 16 weeks to induce atherosclerosis. Immunohistochemical staining of the cellular components (macrophages and smooth muscle cells) of aortic atherosclerotic lesions revealed a significant increase (52%) in the macrophage-positive area in only male transgenic rabbits compared with that in the nontransgenic littermates. However, both male and female transgenic rabbits showed a significant decrease (45% in males and 31% in females) in the smooth muscle cell-positive area compared with that of their control littermates. The effects of macrophage-secreted UII on the plaque cellular components were independent of plasma lipid level. Meanwhile the wild-type rabbits were continuously subcutaneously infused with urantide (5.4 µg· kg^-1· h^-1) using osmotic mini-pumps. Infusion of urantide exerted effects opposite to those caused by UII, as it significantly decreased the macrophage-positive area in male wild-type rabbits compared with that of control rabbits. In cultured human umbilical vein endothelial cells, treatment with UII dose-dependently increased the expression of the adhesion molecules VCAM-1 and ICAM-1, and this effect was partially reversed by urantide. The current study provides direct evidence that macrophage-secreted UII plays a key role in atherogenesis. Targeting UII with urantide may promote plaque stability by decreasing macrophage-derived foam cell formation, which is an indicator of unstable plaque.

T-cell tolerance and exhaustion in the clearance of Echinococcus multilocularis: role of inoculum size in a quantitative hepatic experimental model

The local immune mechanisms responsible for either self-healing or sustained chronic infection are not clear, in the development of E. multilocularis larvae. Here, we developed a suitable experimental model that mimics naturally infected livers, according to the parasite load. We demonstrated that local cellular immunity and fibrogenesis are actually protective and fully able to limit metacestode growth in the liver of low or medium dose-infected mice (LDG or MDG), or even to clear it, while impairment of cellular immunity is followed by a more rapid and severe course of the disease in high dose-infected mice (HDG). And recruitment and/ or proliferation of memory T cells (including CD4 Tem, CD8 Tcm and CD8 Tem) and imbalance of T1/T2/T17/Treg-type T cells in liver were not only associated with clearance of the parasite infection in LDG, but also with increased hepatic injury in HDG; in particular the dual role of CD8 T cells depending on the parasite load and the various stages of metacestode growth. Besides, we first demonstrate the association between LAG3- or 2B4-expressing T cells exhaustion and HD inocula in late stages. Our quantitative experimental model appears fully appropriate to study immunomodulation as a therapeutic strategy for patients with Alveolar Echinococcosis.

Immunoregulation in larval Echinococcus multilocularis infection

Alveolar echinococcosis (AE) is a clinically very severe zoonotic helminthic disease, characterized by a chronic progressive hepatic damage caused by the continuous proliferation of the larval stage (metacestode) of Echinococcus multilocularis. The proliferative potential of the parasite metacestode tissue is dependent on the nature/function of the periparasitic immune-mediated processes of the host. Immune tolerance and/or down-regulation of immunity are a marked characteristic increasingly observed when disease develops towards its chronic (late) stage of infection. In this context, explorative studies have clearly shown that T regulatory (Treg) cells play an important role in modulating and orchestrating inflammatory/immune reactions in AE, yielding a largely Th2-biased response, and finally allowing thus long-term parasite survival, proliferation and maturation. AE is fatal if not treated appropriately, but the current benzimidazole chemotherapy is far from optimal, and novel options for control are needed. Future research should focus on the elucidation of the crucial immunological events that lead to anergy in AE, and focus on providing a scientific basis for the development of novel and more effective immunotherapeutical options to support cure AE by abrogating anergy, anticipating also that a combination of immuno- and chemotherapy could provide a synergistic therapeutical effect.

The Potential Role of Th9 Cell Related Cytokine and Transcription Factors in Patients with Hepatic Alveolar Echinococcosis

Human alveolar echinococcosis (AE) is a lethal parasitic infectious disease which may lead to liver failure if left untreated. It is caused by the larval stage of the fox tapeworm Echinococcus multilocularis and usually develops a substantial infiltrative occupation in solid organs. During the infection, T helper subsets are known to play crucial role in crosstalk between the parasite and human host. Th9 cells, a new member of CD4⁺ T cell family which is characterized by its specific cytokine IL-9 and transcription factors PU.1 and IRF-4, have been known recently to have a critical role in allergic diseases, and cancers as well as the parasitic infection. To assess the potential role of Th9 cells during the infection, the mRNA levels of IL-9, PU.1, and IRF-4 both in peripheral blood mononuclear cells and in liver tissues were, respectively, detected by using real-time PCR. The plasma concentration levels of IL-9 were detected by using enzyme linked immunosorbent assay (ELISA). Th9 related cytokine IL-9 and transcription factors PU.1 and IRF-4 mRNA levels elevated both in PBMCs, and in hepatic lesion and paralesion tissues in AE patients. This may facilitate the infiltrative growth of the parasite and its persistence in human host.

In vitro induction of lymph node cell proliferation by mouse bone marrow dendritic cells following stimulation with different Echinococcus multilocularis antigens

The immune response of mice experimentally infected with Echinococcus multilocularis metacestodes becomes impaired so as to allow parasite survival and proliferation. Our study tackled the question on how different classes of E. multilocularis antigens (crude vesicular fluid (VF); purified proteinic rec-14-3-3; purified carbohydrate Em2(G11)) are involved in the maturation process of bone-marrow-derived dendritic cells (BMDCs) and subsequent exposure to lymph node (LN) cells. In our experiments, we used BMDCs cultivated from either naïve (control) or alveolar echinococcosis (AE)-infected C57BL/6 mice. We then tested surface markers (CD80, CD86, MHC class II) and cytokine expression levels (interleukin (IL)-10, IL-12p40 and tumour necrosis factor (TNF)-α) of non-stimulated BMDCs versus BMDCs stimulated with different Em-antigens or lipopolysaccharide (LPS). While LPS and rec-14-3-3-antigen were able to induce CD80, CD86 and (to a lower extent) MHC class II surface expression, Em2(G11) and, strikingly, also VF-antigen failed to do so. Similarly, LPS and rec-14-3-3 yielded elevated IL-12, TNF-α and IL-10 expression levels, while Em2(G11) and VF-antigen didn't. When naïve BMDCs were loaded with VF-antigen, they induced a strong non-specific proliferation of uncommitted LN cells. For both, BMDCs or LN cells, isolated from AE-infected mice, proliferation was abrogated. The most striking difference, revealed by comparing naïve with AE-BMDCs, was the complete inability of LPS-stimulated AE-BMDCs to activate lymphocytes from any LN cell group. Overall, the presenting activity of BMDCs from AE-infected mice seemed to trigger unresponsiveness in T cells, especially in the case of VF-antigen stimulation, thus contributing to the suppression of clonal expansion during the chronic phase of AE infection.

Echinococcus multilocularis and its intermediate host: a model of parasite-host interplay

Host-parasite interactions in the E. multilocularis-intermediate host model depend on a subtle balance between cellular immunity, which is responsible for host's resistance towards the metacestode, the larval stage of the parasite, and tolerance induction and maintenance. The pathological features of alveolar echinococcosis. the disease caused by E. multilocularis, are related both to parasitic growth and to host's immune response, leading to fibrosis and necrosis, The disease spectrum is clearly dependent on the genetic background of the host as well as on acquired disturbances of Th1-related immunity. The laminated layer of the metacestode, and especially its carbohydrate components, plays a major role in tolerance induction. Th2-type and anti-inflammatory cytokines, IL-10 and TGF-β, as well as nitric oxide, are involved in the maintenance of tolerance and partial inhibition of cytotoxic mechanisms. Results of studies in the experimental mouse model and in patients suggest that immune modulation with cytokines, such as interferon-α, or with specific antigens could be used in the future to treat patients with alveolar echinococcosis and/or to prevent this very severe parasitic disease.

Serum sIL-2R, TNF-α and IFN-γ in alveolar echinococcosis

AIM: To approach the relationship between alveolar echinococcosis (AE) pathology and level of sIL-2R,TNF-α and IFN-γ in sera and the significance of cytokines in development of AE.

METHODS: After 23 patients with AE were confirmed by ELISA and ultrasound, their sera were collected and the concentrations of sIL-2R,TNF-α and IFN-γ were detected by double antibody sandwich. Twelve healthy adults served as controls. According to the status of livers of AE patients by ultrasound scanning, they were divided into 4 groups: P₂, P₃, P₄ groups and C group (control). Average of concentrations of sIL-2R,TNF-α and IFN-γ in homologous group was statistically analyzed by both ANOV and Newman-Keuls, respectively.

RESULTS: The mean of sIL-2R in P₂ group was 97 ± 29, P₃: 226 ± 80, P₄: 194 ± 23 and control group (111 ± 30) × 10³ u/L (P < 0.01). The mean of TNF-α in P₂ group was 1.12 ± 0.20, P₃: 3.67 ± 1.96 , P₄: 1.30 ± 0.25 and control group 0.40 ± 0.19 µg/L (P < 0.01). The mean of IFN-γ in P₂ group was 360 ± 20, P₃: 486 ± 15, P₄: 259 ± 19 and control group: 16 ± 2 ng/L (P < 0.01). Judged by ANOV and Newman-Keuls, the mean concentrations of sIL-2R, TNF-α and IFN-γ had a significant difference among groups. Except for P₂ group, the mean sIL-2R between other groups of AE patients had a significant difference (P < 0.05). The mean of TNF-α concentration in P₃ group was the highest (P < 0.01). The mean of IFN-γ concentration in all patients was higher than that in control group (P < 0.01), but there was no difference between AE groups (P > 0.05).

CONCLUSION: Low sIL-2R level indicates an early stage of AE or stable status, per contra, a progression stage. Higher level of TNF-α might be related to the lesion of liver. The role of single IFN-γ is limited in immunological defense against AE and it can not fully block pathological progression.

Echinococcosis and allergy

The larval stages of Echinococcus granulosus and E. multilocularis are involved in parasitic diseases in humans: cystic echinococcosis (CE) ("hydatid disease") and alveolar echinococcosis (AE), respectively. Both diseases and parasites have tight links with allergy because of the immunological characteristics that contribute to maintain the larvae in their human host as well as their potential in inducing clinical anaphylactic reactions in some patients. Clinical observations in patients and data obtained from mass screenings in various countries have identified both forms of echinococcosis as "polar diseases," i.e., diseases where immunological background of the patients was related to the clinical presentation and course. In particular, abortive cases (i.e., spontaneous cures) have been found in many subjects in endemic areas. On the other hand, immune suppression was associated with severe disease. AE especially might be considered as an opportunistic infection. Experimental and clinical studies have shown that Th1-related immune response was associated with protection and Th2-related response was associated with parasite growth. Genetic characteristics of the host are related to both occurrence and severity of AE and are associated with the extent of IL-10 secretion, which is a major feature of chronic progressing echinococcosis. Anaphylactic reactions, including urticaria, edema, respiratory symptoms, and anaphylactic shock due to spontaneous or provoked rupture of the parasitic cyst, are well known in CE. Anaphylactic reactions in AE are far less frequent, and have been observed in rare cases at time of metastatic dissemination of the parasitic lesions. Echinococcus-specific IgE is present in most of the patients and associated with severity. Specific histamine release by circulating basophils stimulated with E. granulosus antigens is present in all patients with CE and AE. Echinococcus allergens include (1) AgB 12-kDa subunit, a protease inhibitor and a potent Th2 inducer; (2) Ag5, a serine protease; (3) EA 21, a specific cyclophilin, with a homology with other types of cyclophilins; (4) Eg EF-1 beta/delta an elongation factor, with a homology with Strongyloides stercoralis EF that shares the same IgE epitope. A clinical cross-reaction with Thiomucase, a mucopolysaccharidase used in arthritis treatment, has recently been published. However, despite the potential risk of allergic reactions, the dogma "never puncture a hydatid cyst" is no longer valid. International experience of therapeutic technique of "puncture, aspiration, injection, re-aspiration" of hydatid cysts developed at the beginning of the 1980s has proved to be successful in a variety of selected indications that have been reviewed by WHO recommendations. A better understanding of the immunological background of echinococcosis in humans has led to new therapeutic developments, such as immunomodulation using interferon alpha. Th2-driven immunological response and IL-10-related tolerance state are common characteristics of atopic allergy and echinococcosis. The example of echinococcosis stresses the ambiguous links that exist between parasitic and allergic diseases, and show the usefulness of comparing these diseases to better understand how immune deviation may lead to pathological events and to find new therapeutic and.or preventive agents.

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.

Resistance/susceptibility to Echinococcus multilocularis infection and cytokine profile in humans. II. Influence of the HLA B8, DR3, DQ2 haplotype

Differences have been shown between HLA characteristics of patients with different courses of alveolar echinococcosis (AE). Notably the HLA B8, DR3, DQ2 haplotype was associated with more severe forms of this granulomatous parasitic disease. We compared IL-10, IL-5, interferon-gamma (IFN-gamma) and tumour necrosis factor (TNF) secretion by peripheral blood mononuclear cells (PBMC) isolated from eight HLA-DR3+, DQ2+, B8+ AE patients and from 10 HLA-DR3-, DQ2-, B8- patients after non-specific mitogenic and specific Echinococcus multilocularis antigenic in vitro stimulation. PBMC from seven HLA-DR3+, DQ2+, B8+ healthy subjects and nine HLA-DR3-, DQ2-, B8- subjects were also studied as controls. PBMC from AE patients with HLA DR3+, DQ2+ haplotype secreted higher levels of IL-10 without any stimulation and after specific antigenic stimulation than did patients without this haplotype. Higher levels of IL-5 and IFN-gamma were also produced by these patients' PBMC after stimulation with non-purified parasitic antigenic preparations; however, the specific alkaline phosphatase antigen extracted from E. multilocularis induced only Th2-type cytokine secretion. A spontaneous secretion of TNF by HLA DR3+, DQ2+ B8+ AE patients was also found. These results suggest that HLA characteristics of the host can influence immune-mediated mechanisms, and thus the course of AE in humans; specific antigenic components of E. multilocularis could contribute to the preferential Th2-type cytokine production favoured by the genetic background of the host.

Resistance/susceptibility to Echinococcus multilocularis infection and cytokine profile in humans. I. Comparison of patients with progressive and abortive lesions

To clarify the role of Th1- and Th2-type cytokines in the various outcomes of human alveolar echinococcosis (AE), the cytokine immune response of self-cured patients was studied and compared with those of progressive AE patients and healthy subjects. Self-cured patients were divided into two groups according to the following clinical features: subjects who had positive Echinococcus multilocularis serologies and hepatic calcifications typical of AE were classified as 'abortive AE' patients, and those who had positive E. multilocularis serologies but no hepatic lesions or calcifications detectable by ultrasonography were classified as 'positive serology' subjects. Secretions of IL-5, IL-10 and interferon-gamma, and expression of IL-5 mRNA were evaluated in peripheral blood mononuclear cells (PBMC) stimulated in vitro with the mitogen phytohaemagglutinin-C or specific E. multilocularis antigenic preparations. The cytokine profile of abortive AE patients was the opposite of that observed in progressive AE patients. An intermediate profile was observed in positive serology subjects. PBMC from abortive AE patients, whether non-stimulated or stimulated with PHA and antigenic preparations, secreted significantly lower levels of IL-10 than those isolated from progressive AE patients. Our observations seem to confirm the regulatory role of IL-10 in the immunopathology of human AE.

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.

Experimental investigations on the B and T cell immune response in primary alveolar echinococcosis

Susceptibility/resistance of the intermediate host to alveolar echinococcosis (AE) seems to be based on hitherto unknown immunological mechanisms, possibly involving the activation of different CD4+ T cell immune responses (Th1/Th2). Mice of two strains previously characterized as 'susceptible' (C57BL/6 J) and 'resistant' (C57BL/10 J) to secondary AE were orally infected with eggs of Echinococcus multilocularis and the course of infection was analysed by macroscopical, pathohistological and immunohistochemical examinations of the lymphocytes and cytokines participating in the periparasitic granulomas and by serological examinations of cytokines and E. multilocularis-specific antibodies. Although differences in the extent of parasitic growth were seen between the two groups, the composition of the granulomas was quite similar with CD4+ cells being the dominant lymphocyte subpopulation, succeeded by B cells and CD8+ cells. Interferon (IFN)-gamma-, interleukin (IL)-2- and IL-4-expressing cells could not be detected in the lesions of the early phase of the infection, possibly indicating the host's immunosuppression, but were present at the end. IL-10 was the most prominent cytokine throughout the course of the disease. Serological analyses of the cytokine concentrations revealed small amounts at the beginning and high levels at the end of the infection. The pattern of cytokine response was similar for IL-4 in both strains, but different for IL-2 and IL-10 in the late phase, when the C57BL/10 J strain developed higher levels than the C57BL/6 J strain. Correspondingly only small amounts of immunoglobulin (Ig)M, IgG1, IgG2a and IgG3 could be detected at the beginning of disease, followed by higher levels at the end. The courses of antibody titres were similar in both groups except IgG3, which was more pronounced in the C57BL/10 J strain. Parasite-specific IgG2b could neither be detected in the C57BL/6 J nor in the C57BL/10 J strain by the test system used. The results of the study suggest both subsets of CD4+ T cells (Th1 and Th2) being involved in murine primary alveolar echinococcosis. A strict differentiation of mice in susceptible and resistant animals based on the activation of different CD4+ T cell immune responses (Th1 'resistant' and Th2 'susceptible') should be avoided.

Interleukin (IL)-4, IL-10 and IL-12 profile in serum of patients with alveolar echinococcosis

Alveolar echinococcosis (AE), caused by Echinococcus multilocularis (E.m.), provokes a characteristic immune response. Based mainly on in vitro studies, Th2 dominated immunity is associated with increased susceptibility to disease, while Th1 cell activation is assumed to induce protective immunity. We investigated serum levels of interleukin (IL)4, IL-10, and IL-12 in 40 AE patients and 20 controls to assess Th1/Th2 cell activation in vivo. Significantly higher levels of IL-10 were found in AE patients (P = 0.003) than in controls, with a tendency to higher concentrations in progressive cases. In contrast, IL-4 was only measurable in a minority of patients and controls. IL-12 levels (measured with an ELISA that detects both the p35/p40 heterodimer and free p40) were comparable between AE patients and controls and showed a similar distribution pattern to IL-10 with regard to disease progression. By using an IL-12-ELISA specific for the heterodimer, only minute amounts of IL-12 were detectable in merely a minority of samples. In conclusion, our data are suggestive of Th2 dominated immune response in AE in vivo.

Zinc status in patients with alveolar echinococcosis is related to disease progression

Zinc is an essential trace element for immune function that plays a role in immune response against parasites. To determine a possible relationship between zinc level and disease status in alveolar echinococcosis (AE), we investigated serum concentrations of zinc, immunoglobulin (Ig)E, IgG, and C-reactive protein (CRP) in 40 AE patients and 20 controls. Patients were classified into three groups: group A: patients after curative surgery, group B: patients with stabilized disease, group C: patients with progressive disease. Patients showed significantly higher levels of IgE and IgG than controls. Amounts of IgE and IgG were related to disease severity, achieving highest levels in group C and lowest in group A. Zinc levels were comparable in patients and controls. However, there was an obvious association between zinc concentration and disease severity. Zinc was far below the normal range in group C (median 9.2 micromol/l) and significantly diminished compared to group B and controls. An inverse pattern was seen for CRP. In conclusion, lowered zinc concentration in progressive cases may be caused by enhanced immune activation but consumption of zinc by the growing parasite may also play a role. Furthermore, decreased zinc levels may contribute to the observed immunosuppression in AE.

Intestinal and systemic humoral immunological events in the susceptible Balb/C mouse strain after oral administration of Echinococcus multilocularis eggs

The aim of the study was to investigate the systemic and, for the first time, the intestinal humoral events in the susceptible Balb/C mouse strain after oral administration of Echinococcus multilocularis eggs. Thirty-one mice were divided into three groups; W-2, W-8 and control group. Each mouse of the W-2 and W-8 groups was orally infected with 1,500 E. multilocularis eggs, two weeks and eight weeks before sacrifice respectively. Control group mice received phosphate buffer saline. Measurement of anti-E. multilocularis and non-specific IgG, IgA and IgM, and of a transudation marker, albumin, were performed in serum and intestinal washings by a time-resolved immunofluorometric assay. These results were complemented by microscopic examination of the intestinal mucosa. This infection model is well-suited to the study of mucosal immunity during alveolar echinococcosis. It showed a major specific intestinal response in the early stage of the disease whereas the systemic response predominated later in the disease. Histopathological studies and calculation of the relative coefficient of excretion of Ig also confirmed that the presence of the parasite, even during a short period, was responsible for a local immunological and inflammatory response and for a change in mucosal permeability. Mucosal immunity could thus play a role in tolerance induction against E. multilocularis that could be a prerequisite for the subsequent development of the larvae in the liver, and for the occurrence of the parasitic disease, 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.

Evaluating the activity of liver cystic echinococcosis using the delayed-hypersensitivity skin reaction to common antigens

When 11 patients with active liver cystic echinococcosis were tested with a commercial, delayed-hypersensitivity, skin test (DHST) to seven common antigens (Multitest; Merieux Institute, Lyon) they all reacted less than 30 patients with non-parasitic liver cysts, who had normal reactions. This immunosuppression in cystic echinococcosis was transient, as DHST performed within a few months of treatment were normal. DHST may help in evaluating the activity of Echinococcus granulosus cysts.

Echinococcus multilocularis: parasite-specific humoral and cellular immune response subsets in mouse strains susceptible (AKR, C57B1/6J) or 'resistant' (C57B1/10) to secondary alveolar echinococcosis

Parasite-specific humoral and cell-mediated immune responses were investigated in highly susceptible (AKR and C57B1/6J) and relatively resistant (C57B1/10) mice undergoing secondary alveolar echinococcosis (infection with Echinococcus multilocularis metacestode). The parasite-specific proliferative immune response of lymph node cells upon in vitro antigen stimulation remained weak in all three mouse strains. By day 30 p.i., CD4+ lymphoblast cells dominated the total population of blast cells in all three mouse strains. There was, however, an unexpectedly high proportion of CD8+ blast cells; by day 90 p.i., a marked proportional increase in CD8+ cells was seen in susceptible (AKR and C57B1/6J), but not in resistant (C57B1/10) mice. Susceptible, but not resistant mice exhibited a significantly decreased responsiveness of lymph node cells to concanavalin A (Con A) stimulation on day 90 p.i. Analysis of the humoral immune response by ELISA showed that resistance in C57B1/10 mice was associated with the ability of the host to synthesize antibodies to Em2 of the IgG3 and IgG1 isotype. Em2 is a lectin-binding carbohydrate antigen of the laminated layer. In susceptible AKR and C57B1/6J mice, low levels of anti-Em2 antibodies of the IgG2a isotype were detected. Anti-Em2 antibodies of the IgG3/IgG1 isotype, however, were absent. Differences in subclass-specific IgG responses were confirmed by immunoblot analyses. Our findings suggest that differences in antigen recognition (with respect to subsets of humoral and cellular immune components), probably controlled by non-H-2 gene(s), coupled to immune suppression modulated by CD8+ cells and/or respective cytokines, may determine susceptibility or resistance in experimental infection with E. multilocularis.

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.

Lymphocyte engraftment conveys immunity and alters parasite development in scid mice infected with Echinococcus multilocularis

Severe combined immune-deficient (scid) mice, which lack functional B- and T-lymphocytes, were infected with Echinococcus multilocularis larval tissue before or after reconstitution with lymphoid cells from immunocompetent donor mice. Untreated scid mice were highly susceptible to E. multilocularis infection, while scid mice reconstituted with purified lymphocytes derived from either infected or uninfected normal donor mice were capable of almost totally suppressing the growth of the larval cyst mass. The somatic development of the larval parasite varied according to the infection status of the cell donor, with protoscolices forming in scid mice reconstituted with cells from uninfected normal mice but not in those receiving cells from infected normal mice. These results confirm earlier findings that lymphocytes are important in suppressing the growth of E. multilocularis cysts in the intermediate host and also indicate that protoscolex development is influenced by lymphocytes or their products.

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.

Molecular and immunological diagnosis of echinococcosis

Echinococcosis is an infectious disease of humans caused by the larval (metacestode) stage of the cestode species Echinococcus granulosus (cystic echinococcosis or hydatid disease) or Echinococcus multilocularis (alveolar echinococcosis or alveolar hydatid disease). Clinical manifestations depend primarily on localization and size of hepatic lesions and may include hepatomegaly, obstructive jaundice, or cholangitis. Prognostically, alveolar echinococcosis is considered similar to liver malignancies, including a lethality rate of 90% for untreated cases. Diagnosis is based on imaging techniques coupled with immunodiagnostic procedures. Antibody detection tests for E. multilocularis have markedly improved with the use of affinity-purified Em2 antigen and recombinant antigen II/3-10 in enzyme immunoassays. Antigens of corresponding quality for E. granulosus are still unavailable. The detection of circulating antigens and immune complexes in the sera of patients with cystic echinococcosis, the demonstration of in vitro lymphocyte proliferation in response to stimulation with Echinococcus antigens, and the discrimination of serum immunoglobulin isotype activity to various Echinococcus antigens in both cystic and alveolar echinococcosis have been suggested for diagnostic purposes as well as for monitoring patients after treatment. New diagnostic molecular tools include DNA probes for Southern hybridization tests and polymerase chain reaction for the amplification of E. multilocularis and E. granulosus species-specific DNA fragments.

Effects of cyclosporin A on the course of murine alveolar echinococcosis and on specific cellular and humoral immune responses against Echinococcus multilocularis

The effects of cyclosporin A (CsA) on Echinococcus multilocularis (E. multilocularis) metacestode growth, and on the specific immune responses of the hosts, were examined in AKR mice. Mice were intra-peritoneally infected with a metacestode homogenate. CsA (40 mg kg(-1) day(-1)) was injected subcutaneously from the 45th day after infection (Group 1), and from the day before infection (Group 2) until the day of autopsy (days 125 and 80, respectively). Results showed that unlike ths situation with some other helminthiases, CsA had no antiparasitic effect, although it lengthened the maturation time of protoscoleces in Group 1. The parasitic burden, unmodified in Group 1, was significantly enhanced in Group 2. This enhancement was associated with a decrease in antibody levels, whereas the delayed-type hypersensitivity was decreased in the two groups. These results confirm the role of cellular immunity in controlling the first stages of the larval development of E. multilocularis and indicate the necessity for a careful follow-up of any recurrence of alveolar echinococcosis in patients treated with CsA after liver transplantation.

Cellular immunity in experimental Echinococcus multilocularis infection. II. Sequential and comparative phenotypic study of the periparasitic mononuclear cells in resistant and sensitive mice

Cellular immune responses have been shown to be associated with differential evolutions of E. multilocularis infection in intermediate hosts. A relationship between course of delayed-type hypersensitivity (DTH) against parasitic antigens and receptivity of murine strains has been demonstrated recently. The aim of this study was to correlate resistance and sensitivity to E. multilocularis infection with the phenotypic patterns of cells within the periparasitic granuloma. Evolution of the ratios, macrophages/T lymphocyte and Ly1/Ly2 T lymphocytes, was associated with the receptivity of the strains. Persistence of numerous L3T4 + T lymphocytes and low numbers of macrophages and Ly2 + T lymphocytes were observed in the 'resistant' C57BL.10 mice. Comparison of the results with course of the DTH against E. multilocularis antigens showed that the particular phenotypic pattern observed in resistant mice was associated with a particular profile of DTH after infection. These results and similar observations in human alveolar echinococcosis suggest that cell composition of the periparasitic granuloma might be of crucial importance in controlling the spontaneous development of E. multilocularis larvae in the intermediate host.