This study investigated the immunological aspects of Entamoeba histolytica infection in Syrian hamsters. Immunization of hamsters by an intradermal injection with live axenic amoebae, conferred complete protection against amoebic liver abscess. Protection was achieved with homologous or heterologous strains of E. histolytica and was dose-dependent. Combination of thymectomy and anti T-cell serum treatment significantly increased the size of liver abscess and metastatic dissemination of the parasite. It was shown that a cell-mediated immune response controls the healing of skin ulcers in vaccinated animals and thus confers on them resistance to intrahepatic amoebic challenge infection. Resistance to hepatic infection with E. histolytica can be passively transferred to normal recipients with sensitized cells, but not with immune serum. Sensitized cells from vaccinated, protected or infected animal kill E. histolytica trophozoites in vitro. Splenectomy reduces the resistance of hamsters to amoebic infection. It is suggested that macrophages are required in the host defence against the establishment of amoebic abscess in the liver and dissemination of amoebae to other organs.

No description available.

Invasive amebiasis, caused by the protozoan parasite Entamoeba histolytica, is one of the leading parasitic causes of mortality worldwide, and there are no vaccines available to control the disease. The heavy subunit of the E. histolytica Gal-lectin is regarded as a potential subunit vaccine candidate. A Th1 (cell-mediated) immune response is protective against invasive amebiasis, and DNA vaccination is a strategy to induce such a response against specific antigens. The objective of this study was to construct and test a Gal-lectin-based DNA vaccine against E. histolytica. DNA encoding as 894--1081 of the Gal-lectin heavy subunit was resynthesized using a gerbil codon frequency bias and inserted in a mammalian expression vector to generate the DNA vaccine pCISToGL6. Balb/c mice vaccinated intradermally developed a Gal-lectin-specific cellular immune response, as well as an anti-Gal-lectin humoral immune response. Serum antibodies recognized a recombinant portion of the Gal-lectin heavy subunit by immunoblot and ELISA, and bound to native Gal-lectin on the surface of live trophozoites, inhibiting adherence to target cells. The Gal-lectin-specific serum antibodies were of the IgG2a isotype, indicating that a Th1 response was stimulated by the vaccine. We were also interested in using DNA encoding IL-12, IL-18 or GM-CSF as genetic adjuvants co-injected with pCISToGL6 to potentiate the immune response. Since the DNA vaccine was destined to confer protection in the gerbil model of invasive amebiasis, we cloned gerbil IL-12 (p35 and p40), IL-18 and its convertase caspase-1, and GM-CSF. The proteins were expressed in mammalian cells and showed bioactivity in vitro. Taken together, these results have laid the foundation to optimize and test a working Gal-lectin with co-stimulatory molecules to elicit a Th1 immune response for protective immunity against invasive amebiasis.

Entamoeba histolytica, etiological agent of amebiasis, continues to be a significant threat to human health worldwide. The disease affects 10% of the world's population and leads to an estimated 100, 000 deaths a year. The parasite's surface Gal-lectin is an immunodominant protein that also mediates colonization and pathogenicity. The Gal-lectin is the most promising vaccine candidate against amebiasis. However, the immune mechanisms involved in protection against disease remain unclear. The objective of this study was to characterize the immunological basis of the host defense mechanisms using a Gal-lectin based vaccine. Exposure of the Gal-lectin with immature dendritic cells increased cell maturation and activation and upregulated co-stimulatory molecules and pro-inflammatory cytokines production. Dendritic cell activation was dependent on NF-kappaB and MAPK activation. In vaccination studies, the adjuvant effect of CpG-ODN, a synthetic oligodeoxynucleotide capable of stimulating Th1 immune responses enhanced the immune response to the Gal-lectin when administered systemically or mucosally. Protected animals had elevated anti-Gal-lectin serum and stool IgA antibodies capable of blocking parasite adherence in vitro. Analysis of cytokine responses in vaccinated and protected animals revealed increased IFN-gamma production compared to controls. Finally, E. histolytica DNA was shown to activate macrophages in a TLR9 and MYD88-dependent manner. Immunized gerbils with Gal-lectin and E. histolytica DNA induced protective immunity against a challenge infection. Taken together, these findings underscore the importance of multivalent subunit vaccines in Th1 mediated immune responses in host defense against amebiasis.

No description available.

No description available.