Molecular and cellular tools in human cystic echinococcosis

Potential role of NF-κB pathway in the immuno-inflammatory responses during human cystic echinococcosis

Cystic echinococcosis (CE) induces in the human host innate and adaptive immune response that plays an important role in controlling the immunopathogenesis. Due to the crucial role of nuclear factor kappa B (NF-κB) in regulating immuno-inflammatory processes, we investigated its potential contribution in systemic and local immuno-inflammatory responses in primary CE patients and relapsed patients. The expression of NF-κB and inducible nitric oxide synthase (iNOS) was analyzed in peripheral blood mononuclear cells (PBMC) as well as in pericystic layer of pulmonary hydatid cysts from Algerian primary CE patients and relapsed patients. Tumor necrosis factor alpha (TNF-α) and nitric oxide (NO) production was evaluated in plasma samples. Our results showed high iNOS and NF-κB expression in both PBMCs and pericystic histiocytes from primary CE patients. In addition, substantial amounts of systemic NO and TNF-α were detected in the same patients. Remarkably, relapsed patients exhibited a low NF-κB and iNOS expression associated with low amounts of plasmatic TNF-α and NO. Collectively, NF-κB/iNOS pathway is involved in the host defense mechanisms at the systemic and local level during primary CE. Our results indicate that the inhibition of this pathway in relapsed patients will attenuate protective immunity and promote parasite escape. This study allowed to identify a novel predictive biomarkers of hydatidosis.

Immunogenetics of human echinococcosis

Susceptibility and resistance to human Echinococcus infection and disease, although poorly understood, appear to reflect a complex interaction of parasite and host immunological and genetic factors. Disease stage, progression, and prognosis following treatment appear to be strongly influenced by cytokine and antibody profiles, and more recent evidence has suggested an important role of dendritic cells (DCs) and T regulatory cells (Tregs) in immunomodulation. Microarrays have supported these findings, highlighting both known and novel pathways involved in chronic murine disease. Genetic studies to date have been few and with limited success. Advanced genomic approaches, such as genome-wide association studies (GWAS), may provide further insight to identify the relevant pathways involved, thereby facilitating a new approach for the development of new clinical therapies.

Host-parasite relationship in cystic echinococcosis: an evolving story

The larval stage of Echinococcus granulosus causes cystic echinococcosis, a neglected infectious disease that constitutes a major public health problem in developing countries. Despite being under constant barrage by the immune system, E. granulosus modulates antiparasite immune responses and persists in the human hosts with detectable humoral and cellular responses against the parasite. In vitro and in vivo immunological approaches, together with molecular biology and immunoproteomic technologies, provided us exciting insights into the mechanisms involved in the initiation of E. granulosus infection and the consequent induction and regulation of the immune response. Although the last decade has clarified many aspects of host-parasite relationship in human cystic echinococcosis, establishing the full mechanisms that cause the disease requires more studies. Here, we review some of the recent developments and discuss new avenues in this evolving story of E. granulosus infection in man.

Molecular characterization of antigen B2 subunit in two genotypes of Echinococcus granulosus from Indian bubaline isolates, its stage specific expression and serological evaluation

Echinococcus granulosus is a parasitic helminth which affects both man and animals. During infection with larval stage of the organism secretory and membrane-bound (S/M) proteins play a meaningful role for evasion of immune system. Antigen B (AgB) is one of them. Present investigation has defined sequence diversity of AgB2 subunit of cattle and buffalo isolates of the organism. A total of 55 isolates were screened by polymerase chain reaction based single stranded conformation polymorphism (PCR-SSCP). Subsequently, six conformers could be detected. Based on predicted amino acid sequences of 90 amino acid residues, three clusters could be deduced. Sequence information of two buffalo isolates was homologous to AgB4 indicating gene switching phenomenon in between closely related isoforms. Numerical value of Tajima's D test proved negative selection pressure. Using artificial neural network (ANN), B cell linear epitope and stretches of agretope were predicted. Three clusters could be defined on the basis of B cell linear epitope. Out of three clusters, two showed more than 50% binding propensity with same MHCII alleles whereas, cluster 3 exhibited binding propensity with other MHCII alleles (DRB1_1501, DRB1_1502). Relative expression of AgB2 was more in active cysts (1.636 ± 0.092) followed by degenerating (0.449 ± 0.037) and calcified (0.255 ± 0.008). This result suggested that relative expression of AgB2 declines with progression of the disease. Using recombinant AgB2 sensitivity, specificity and accuracy of the ELISA test was 96.7, 94.7 and 95.9%, respectively. No cross reactivity was found with common cestode and trematode infected cattle and buffalo because cross reactive antigen was expressed intracellularly. Finally, this was concluded that AgB2 is the suitable immunological marker for detection, diagnosis and progression of the disease.

Human cystic echinococcosis: old problems and new perspectives

Cystic echinococcosis (CE) is a widespread chronic endemic helminthic disease caused by infection with metacestodes of the tapeworm Echinococcus granulosus. CE affects humans and has a worldwide prevalence of approximately six million. In this review, we discuss current findings in diagnosis and clinical management of CE and new concepts relating to E. granulosus molecules that directly modulate the host immune responses favouring a strong anti-inflammatory response and perpetuating parasite survival in the host. New insights into the molecular biology of E. granulosus will improve considerably our knowledge of the disease and will provide new potential therapeutic applications to treat or prevent inflammatory immune-mediated disease.

Molecular cross-talk in host-parasite relationships: the intriguing immunomodulatory role of Echinococcus antigen B in cystic echinococcosis

Cystic echinococcosis (CE), a zoonosis caused by the development of Echinococcus granulosus tapeworm larvae in the internal organs of ungulates and humans, continues to pose a major public health burden in underdeveloped and industrialised areas worldwide. Research designed to improve parasitic disease control and find out more about parasite biology has already identified a number of E. granulosus antigenic molecules. The major E. granulosus immunomodulant antigen isolated from hydatid fluid is antigen B, a 120 kDa polymeric lipoprotein consisting of various 8 kDa subunits. By inhibiting elastase activity and neutrophil chemotaxis and eliciting a non-protective Th2 cell response, antigen B helps the parasite evade the human response. In this review, we briefly discuss current information on the molecular characteristics and immunomodulatory properties of E. granulosus antigen B. Besides focusing on findings that provide intriguing insights into the complex interplay between host and parasite, we suggest how this information could extend the current therapeutic options in inflammatory diseases.

Immunomodulatory mechanisms during Echinococcus granulosus infection

The pathologic events that ensue after humans ingest the eggs of Echinococcus granulosus and continue while cystic echinococcosis develops, provide an excellent example illustrating the evasive strategies helminth parasites use to develop, progress and cause chronic disease. The hydatid cyst secretes and exposes numerous immunomodulatory molecules to the host's immune system. By characterizing these molecules we can understand the mechanisms that E. granulosus uses for increasing the efficiency and persistency of infection in the host. These molecules modulate both the innate and adaptive arms of the immune response and appear to target cellular and humoral responses. In this review, we discuss recent advances in the immunobiology of host-E. granulosus interactions that provide intriguing insights into the complex interplay between host and parasite that ultimately facilitates parasite survival.

Echinococcus granulosus antigen B impairs human dendritic cell differentiation and polarizes immature dendritic cell maturation towards a Th2 cell response

Despite inducing a strong host cellular and humoral immune response, the helminth Echinococcus granulosus is a highly successful parasite that develops, progresses, and ultimately causes chronic disease. Although surgery remains the preferred therapeutic option, pharmacological research now envisages antihelminthic strategies. To understand the mechanisms that E. granulosus uses to escape host immunosurveillance and promote chronic infection, we investigated how two hydatid cyst components, purified antigen B (AgB) and sheep hydatid fluid (SHF), act on host dendritic cell (DC) differentiation from monocyte precursors and how they influence maturation of DC that have already differentiated. We evaluated the immunomodulatory potential of these antigens by performing immunochemical and cytofluorimetric analyses of monocyte-derived DCs from healthy human donors. During monocyte differentiation, AgB and SHF downmodulated CD1a expression and upregulated CD86 expression. Compared with immature DCs differentiated in medium alone (iDCs), AgB- and SHF-differentiated cells stimulated with lipopolysaccharide included a significantly lower percentage of CD83(+) cells (P < 10(-4)) and had weaker costimulatory molecule expression. When stimulated with AgB and SHF, iDCs matured and primed lymphocytes towards the Th2 response typical of E. granulosus infection. SHF and particularly AgB reduced the production of interleukin-12p70 (IL-12p70) and tumor necrosis factor alpha in lipopolysaccharide-stimulated iDCs. Anti-IL-10 antibodies increased the levels of IL-12p70 secretion in AgB- and SHF-matured DCs. AgB and SHF induced interleukin-1 receptor-associated kinase phosphorylation and activated nuclear factor-kappaB, suggesting that Toll-like receptors could participate in E. granulosus-stimulated DC maturation. These results suggest that E. granulosus escapes host immunosurveillance in two ways: by interfering with monocyte differentiation and by modulating DC maturation.

Screening of an Echinococcus granulosus cDNA library with IgG4 from patients with cystic echinococcosis identifies a new tegumental protein involved in the immune escape

The worldwide problem of chronic Echinococcus granulosus disease calls for new parasite-derived immunomodulatory molecules. By screening an E. granulosus cDNA library with IgG4 from patients with active cystic echinococcosis, we identified a cDNA that encodes a predicted partial protein that immunofluorescence studies localized in the protoscolex tegument and on the germinal layer of cyst wall. We named this protein EgTeg because the 105 amino acid sequence scored highest against a family of Schistosoma tegumental proteins. Evaluating the role of EgTeg in the human early inflammatory response we found that EgTeg significantly inhibited polymorphonuclear cell (PMN) chemotaxis. Cytometric analysis of intracellular cytokines disclosed a significantly higher percentage of cells producing IL-4 than IFN-gamma (P = 0.001, Student's t-test) in T lymphocytes from patients with cystic echinococcosis stimulated with EgTeg. EgTeg induced weak Th1-dependent proliferation in 42% of patients' peripheral blood mononuclear cells. In immunoblotting (IB) analysis of total IgG and IgG subclass responses to EgTeg in patients with cystic echinococcosis, patients with other parasitoses, patients with cystic lesions and healthy controls, total IgG specific to EgTeg yielded high sensitivity (73%) but low specificity (44%) precluding its use in immunodiagnosis. Conversely, IgG4 specific to EgTeg gave acceptable sensitivity (65%) and high specificity (89%) suggesting its use in immunodiagnosis to confirm ultrasound documented cysts suggestive of E. granulosus. Because the new tegumental antigen EgTeg inhibits chemotaxis, induces IL-4-positive T lymphocytes and noncomplement fixing antibodies (IgG4) it is an immunomodulatory molecule associated with chronic infection.

Echinococcus granulosus-specific T-cell lines derived from patients at various clinical stages of cystic echinococcosis

To investigate the role of T lymphocytes in the immune response to Echinococcus granulosus, using sheep hydatid fluid (SHF) and antigen B (AgB), we generated T-cell lines from patients with active, transitional and inactive hydatid cysts. We established 16 T-cell lines, eight specific to SHF and eight specific to AgB. At surface phenotyping 88-98% of cells displayed the helper/inducer CD4 antigen. In all patients, at all clinical stages of hydatid cyst disease, T-cell stimulation with SHF and AgB invariably amplified a large number of almost identical Vbeta subfamily fragments. Irrespective of antigen-specificity, the two cell lines from the patient with an inactive cyst had a Th1 profile, because they exclusively expressed and produced IFN-gamma. Conversely, the T-cell lines derived from the seven patients with active and transitional hydatid cysts had mixed Th1/Th2 and Th0 clones. The functional characteristics of the 16 T-cell lines differed markedly in the various clinical stages of cystic echinococcosis, thus providing new in vitro evidence that Th1 lymphocytes contribute decisively to the inactive stage of hydatid disease, Th2 lymphocytes in the active and transitional stages. The parasite-specific T-cell lines, especially the two Th1 lines from the patient with an inactive cyst, may help identify Th1 protective epitopes on SHF and AgB.

Molecular and immunological characterization of the C-terminal region of a new Echinococcus granulosus Heat Shock Protein 70

By screening an expression library of Echinococcus granulosus with IgE from sera of patients with cystic echinococcosis (CE) and allergic reactions, we isolated the C-terminal region of a new heat shock protein (HSP)70 of E. granulosus. The protein, named Eg2HSP70, has close homology with the C-terminal region of Dermatophagoides farinae and human HSP70. We investigated the humoral and cell-mediated immune responses to this antigen in patients with CE grouped according to the presence of allergic reactions. Immunoblotting detected total IgG, IgG4 and IgE specific to Eg2HSP70 (83% of sera contained IgG, 31% IgG4 and 57% IgE). No significant difference was found in immunoglobulin percentages according to the presence of allergic reactions. Immunoblotting inhibition showed that no IgG or IgE specific to Eg2HSP70 cross-reacted with D. farinae or human HSP70. Eg2HSP70-stimulated PBMC from 26 patients produced significantly greater amounts of TNF-alpha, IFN-gamma, and IL-10 than unstimulated cultures in all patients, irrespective of the presence of allergic reactions (P < 0.05). They also produced significantly greater amounts of IL-4 than unstimulated cultures exclusively in patients with allergic reactions (P < 0.05). These findings show that Eg2HSP70 is a new antigenic molecule inducing both B and T cell responses.