CpG-Oligodeoxynucleotide Is a Potent Adjuvant with anEntamoeba histolyticaGal-Inhibitable Lectin Vaccine against Amoebic Liver Abscess in Gerbils

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Abstract
The protozoan parasiteEntamoeba histolyticacauses invasive amoebiasis characterized by amoebic dysentery and liver abscesses (ALA). TheE. histolyticagalactose/N-acetyl-d-galactosamine-inhibitable lectin (Gal-lectin), an immunogenic surface molecule involved in colonization and invasion, is a promising vaccine candidate against amoebiasis. Gal-lectin is known to induce Th1 cytokines in macrophages and spleen cells in vitro, and a Th1 response is thought to be protective against ALA. In this study, we report the use of cytosine guanine oligodeoxynucleotide (CpG-ODN) as adjuvant to augment Th1 responses against Gal-lectin in the gerbil model of ALA. Gerbils were vaccinated intramuscularly with the native Gal-lectin plus CpG-ODN or a paired non-CpG control GpC-ODN, and control gerbils received CpG-ODN alone. One week after the last boost gerbils were challenged intrahepatically with 106amoebae. Gerbils receiving CpG-ODN as adjuvant with Gal-lectin were completely protected against the development of ALA, whereas 50% of gerbils receiving GpC-ODN and Gal-lectin developed ALA and 85% of controls developed ALA. Stronger lymphoproliferation in response to the Gal-lectin and higher prechallenge titers of serum Gal-lectin-specific antibodies, capable of blocking amoebic adherence, were observed when CpG-ODN was used as adjuvant. Gerbils vaccinated with CpG-ODN and Gal-lectin also had significantly higher levels of gamma interferon, interleukin-12 (IL-12), and IL-2 mRNA than controls. These data indicate that CpG-ODN can enhance the Th1 responses, which improve the protective effects of Gal-lectin. This is the first report of the use of CpG as a potent Th1 adjuvant with Gal-lectin to increase protection against ALA formation.

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