Ageing impairs parasite-specific antibody responses in cystic echinococcosis.

Humoral immunity wanes during healthy ageing, increasing susceptibility to infections in the elderly. In this sense, information about parasite infections and human immunosenescence is scarce. Cystic echinococcosis (CE) is an infectious disease caused by the larval stage of the cestode parasite Echinococcus granulosus, whose prevalence in humans shows an increase with host age. Susceptibility to human CE has been associated with humoral immunity to some extent, and, therefore, we have here analysed the influence of host age on the serological profile of young, middle-aged and aged patients. Our results highlighted the detrimental influence of ageing on the intensity and quality of the antiparasite antibody response. Remarkable differences in serological profiles between young and aged individuals were observed. In this sense, through Principal Components Analysis, we identified aged patients as those exhibiting overall less intense antibody responses, mainly in isotypes/subclasses supposed to exert efficient antiparasite activities (eg IgE and IgG1). Thus, these humoral defects could at least partially explain the reported increase in CE prevalence among older individuals, as a weaker immune response in the elderly might facilitate the establishment and maintenance of the parasite infection. Finally, a possible association between age-dependent susceptibility to CE and host immunosenescence is discussed.

Antibody profiling in ultrasound normal individuals with positive serology for cystic echinococcosis.

Cystic echinococcosis is a zoonotic disease caused by the cestode parasite Echinococcus granulosus. In endemic regions, seropositive individuals to E. granulosus usually and markedly outnumber image-confirmed cases of cystic echinococcosis, suggesting that some parasite challenges derive in unsuccessful infection establishments. However, it is still unknown whether such parasite-specific antibodies in healthy individuals might play a role in resistance/susceptibility to the infection. Therefore, we have here analysed the profile of antibodies recognizing E. granulosus antigens in seropositive but ultrasound normal individuals, as well as in surgery-confirmed patients and healthy donors. Our results showed that ultrasound normal individuals exhibited low avidity IgG antibodies, as well as low levels of parasite-specific IgG1 and IgG4 antibodies. In addition, they displayed significant levels of specific IgE, and thus, they revealed a uniquely high IgE:IgG4 ratio. Moreover, high levels of parasite-specific IgM were detected in such individuals, which showed characteristics of natural cross-reacting antibodies. Therefore, our results indicate that ultrasound normal individuals but seropositive for E. granulosus antigens exhibit a distinctive antibody profile. In this regard, possible associations between their antiparasite antibodies and potential resistance mechanisms to cystic echinococcosis are discussed.

Echinococcus granulosus pig strain (G7 genotype) protoscoleces did not develop secondary hydatid cysts in mice.

Echinococcus granulosus, the aetiological agent of cystic hydatid disease, exists as a series of strains or genotypes which differ in biological features. Pig strain (G7 genotype) has been shown to differ from sheep strain (G1 genotype) in phenotypical characters such as intermediate host range, geographical distribution and rate of development of the adult worm. Since in vivo studies of different parasite genotypes can provide insights into host-parasite relationship we analysed for the first time the behaviour of E. granulosus G7 genotype protoscoleces in the murine experimental model. Our results show that G7 protoscoleces were unable to establish a regular infection in mice in contrast to G1 protoscoleces which developed intraperitoneal hydatid cysts. This inability was observed in co-infection experiments, i.e. even in the presence of a controlled immune response that allows G1 genotype protoscoleces establishment. In addition, the implantation of in vitro obtained E. granulosus G7 genotype microcysts resulted in a low percentage of hydatid cysts establishment. These results show a difference in the biological ability of both E. granulosus strains to develop secondary hydatid cysts in mice. We suggest that the comparison of infective and non infective genotypes of E. granulosus in the experimental host can be regarded as a new model to study the mechanisms of infection of Echinococcus spp. This knowledge could provide helpful information for the development of therapies, drugs and/or vaccines against cystic hydatid disease.

Echinococcus granulosus glycoconjugates induce peritoneal B cell differentiation into antibody-secreting cells and cytokine production.

Helminth parasite infections are associated with predominant Th2-type cytokine responses, and parasite glycoconjugates have been recognized as partially responsible for such immune bias. It has been proved that Echinococcus granulosus evokes a Th2-type cytokine pattern characterized by a high production of IL-4, IL-5, IL-6 and IL-10, and no or mild IFN-γ levels in animal models and in patients with cystic echinococcosis, respectively. Here, we show that E4(+) (a glycoconjugate-enriched fraction from E. granulosus protoscolex) stimulated the secretion of a high concentration of IL-6, followed by IL-10 and TNF-α by normal peritoneal B cells. We determined that E4(+) bound to the surface of peritoneal B cells and induced their activation and, also, triggered the differentiation of peritoneal B cells into IgM-, IgG2b- and IgG3-secreting cells in a T-independent way. Interestingly, the IgM released by E4(+) -stimulated peritoneal B cells from normal mice recognized protoscolex antigens. Results showed that, after the encounter with antigens from E. granulosus protoscolex, peritoneal B cells are a source of Th2-type cytokines and polyclonal antibodies, some of which recognize parasite antigens, suggesting that peritoneal B cells can condition the outcome of the infection.

Identification of Echinococcus granulosus microRNAs and their expression in different life cycle stages and parasite genotypes.

The aetiological agent of cystic hydatid disease, the platyhelminth parasite Echinococcus granulosus, undergoes a series of metamorphic events during its complex life cycle. One of its developmental stages, the protoscolex, shows a remarkable degree of heterogeneous morphogenesis, being able to develop either into the vesicular or strobilar direction. Another level of complexity is added by the existence of genotypes or strains that differ in the range of intermediate hosts where they can develop and form fertile cysts. These features make E. granulosus an interesting model for developmental studies. Hence, we focused on the study of the regulation of gene expression by microRNAs (miRNAs), one of the key mechanisms that control development in metazoans and plants and which has not been analysed in E. granulosus yet. In this study, we cloned 38 distinct miRNAs, including four candidate new miRNAs that seem to be specific to Echinococcus spp. Thirty-four cloned sequences were orthologous to miRNAs already described in other organisms and were grouped in 16 metazoan miRNA families, some of them known for their role in the development of other organisms. The expression of some of the cloned miRNAs differs according to the parasite life cycle stage analysed, showing differential developmental expression. We did not detect differences in the expression of the analysed miRNAs between protoscoleces of two parasite genotypes. This work sets the scene for the study of gene regulation mediated by miRNAs in E. granulosus and provides a new approach to study the molecules involved in its developmental plasticity and intermediate host specificity. Understanding the developmental processes of E. granulosus may help to find new strategies for the control of cystic hydatid disease, caused by the metacestode stage of the parasite.