Intranasal Immunization with Gal-Inhibitable Lectin plus an Adjuvant of CpG Oligodeoxynucleotides Protects against Entamoeba histolytica Challenge

Abstract

The development of an effective amebiasis vaccine could improve child health in the developing world, reducing cases of amebic colitis and liver abscess. An ideal vaccine would be comprised of a well-characterized parasite antigen and an adjuvant, which would have high potency while driving the immune response in a Th1 direction. This study describes a mucosal vaccine composed of the Entamoeba histolytica galactose/N-acetyl-Dgalactosamine-inhibitable lectin (Gal-lectin) and CpG oligodeoxynucleotides (CpG-ODN). The Gal-lectin is a protein involved in parasite virulence and adherence and is known to activate immune cells, while CpG-ODN are known to be potent inducers of type 1-like immune responses. We demonstrated that intranasal administration of the vaccine resulted in strong Gal-lectin-specific Th1 responses and humoral responses. Vaccination induced the production of Gal-lectin-specific T cells and the production of the proinflammatory cytokine gamma interferon. Vaccinated animals had detectable serum anti-Gal-lectin immunoglobulin G (IgG) and stool anti-Gal-lectin IgA capable of blocking parasite adherence to target cells in vitro. One week after immunization, gerbils were challenged intrahepatically with live trophozoites. Vaccinated gerbils had no detectable abscesses after day 5, whereas control gerbils developed larger abscesses. These results show that mucosal vaccination with Gal-lectin and CpG-ODN can induce both systemic and humoral immune responses.Entamoeba histolytica is the enteric protozoan parasite which causes amoebic colitis and liver abscess in humans. This parasite is estimated to infect 8% of the world's population, leading to 50,000 deaths annually (36). Amebic colitis is the most common clinical manifestation of disease as the parasite must first colonize the colon. Intestinal infection by E. histolytica and progression to disease could theoretically be prevented by vaccine intervention targeted to block parasite colonization (26,35). E. histolytica trophozoites are able to colonize the human intestine by adhering to colonic mucins and subsequently to epithelial cells via a cell surface lectin (3). This galactose/Nacetyl-D-galactosamine-inhibitable lectin (Gal-lectin) is a heterodimer containing disulfide-linked light and heavy subunits, the latter of which has high binding specificity for galactose and N-acetyl-D-galactosamine residues (29). The Gal-lectin is a prime vaccine candidate as it is an immunogenic molecule able to induce protection against amebic liver abscess (ALA) in rodent models of the disease (16,27,30). Recently, it has also been reported that there is a correlation between the presence of anti-lectin fecal immunoglobulin A (IgA) antibodies and protection from parasite colonization in humans (12, 13). Mucosal immunity against the parasite seems to be required to prevent infection, and there is substantial evidence suggesting that a colonization-blocking vaccine targeting the parasite Gallectin could prevent trophozoite adherence and thus provide protection against subse...

Characterization ofEntamoeba histolyticaIntermediate Subunit Lectin-Specific Human Monoclonal Antibodies Generated in Transgenic Mice Expressing Human Immunoglobulin Loci

“…The adherence is mediated by a galactose (Gal)-and N-acetyl-D-galactosamine (GalNAc)-inhibitable lectin (39). The lectin is a 260-kDa heterodimeric glycoprotein composed of a 170-kDa heavy subunit (Hgl) and a 31-or 35-kDa light subunit (Lgl) (38), and the Hgl is a candidate vaccine for amebiasis (22,27,30). We have demonstrated previously that a 150-kDa intermediate subunit (Igl), which is noncovalently associated with Hgl, also contributes to adherence (13).…”

Use of CpG Oligonucleotides as Mucosal Adjuvants

“…It also stimulated the production of neutralizing IgG anti-Gal lectin in the serum and IgA anti-Gal lectin antibodies in the stool (Ivory and Chadee, 2007). That study, which involved vaccinated gerbils, demonstrated protection from abscess formation after an intrahepatical challenge with live trophozoites.…”

Chew on this: amoebic trogocytosis and host cell killing by Entamoeba histolytica

“…Vaccination with fragments of the Gal/GalNAc lectin heavy chain has been shown to be protective in animal models [5–12]. Treatment with metronidazole is the standard [13, 14], though it has toxic side effects [13] and E. histolytica can develop resistance in vitro [15, 16].…”