Identification of an Epitope on the Entamoeba histolytica 170-kD Lectin Conferring Antibody-mediated Protection against Invasive Amebiasis

Abstract

The emergence of multidrug-resistant organisms and the failure to eradicate infection by a number of important pathogens has led to increased efforts to develop vaccines to prevent infectious diseases. However, the nature of the immune response to vaccination with a given antigen can be complex and unpredictable. An example is the galactose– and N-acetylgalactosamine–inhibitable lectin, a surface antigen of Entamoeba histolytica that has been identified as a major candidate in a vaccine to prevent amebiasis. Vaccination with the lectin can induce protective immunity to amebic liver abscess in some animals, but others of the same species exhibit exacerbations of disease after vaccination. To better understand this phenomenon, we used recombinant proteins corresponding to four distinct domains of the molecule, and synthetic peptides to localize both protective and exacerbative epitopes of the heavy chain subunit of the lectin. We show that protective immunity after vaccination can be correlated with the development of an antibody response to a region of 25 amino acid residues of the lectin, and have confirmed the importance of the antibody response to this region by passive immunization studies. In addition, we show that exacerbation of disease can be linked to the development of antibodies that bind to an NH2-terminal domain of the lectin. These findings are clinically relevant, as individuals who are colonized with E. histolytica but are resistant to invasive disease have a high prevalence of antibodies to the protective epitope(s), compared to individuals with a history of invasive amebiasis. These studies should enable us to develop an improved vaccine for amebiasis, and provide a model for the identification of protective and exacerbative epitopes of complex antigens.

Expression in fibroblasts and in live animals of Entamoeba histolytica polypeptides EhCP112 and EhADH112

“…The humoral response may account for the protection observed in the animals inoculated with the mixture of the plasmids. In fact, studies using both active and passive immunization strategies suggest that certain antibodies to E. histolytica may protect against liver abscesses (Lotter et al, 1997;Seydel et al, 1996;Zhang et al, 1994). The cellular response did not augment in the protected animals, although with these experiments we cannot discard differences in the quality of the cellular response with the different immunization protocols.…”

“…It has been reported that DNA vaccines promote the cellular response more than the humoral one (Kowalczyk & Ertl, 1999), and experimental evidence suggests that the cellular response has a predominant role in protection against amoebiasis (Campbell & Chadee, 1997;Schain et al, 1995), although the role of the humoral response has also been documented (Lotter et al, 1997;Seydel et al, 1996;Zhang et al, 1994).…”

Oral Vaccination with Recombinant Yersinia enterocolitica Expressing Hybrid Type III Proteins Protects Gerbils from Amebic Liver Abscess

“…However, differences in the levels of protection were statistically significant only with Yersinia cells transformed either with YopE-T-170CP or YopE-T-170CR2 (Table 1). The protective potential of 170CR2 to inhibit amebic liver abscess in gerbils has been shown previously (9,10). However, the potential of 170CP to induce protective immunity is surprising, as previous studies have shown that high titers of serum immunoglobulin G anti- bodies to this fragment exacerbate amebic disease (10).…”

“…The protective potential of 170CR2 to inhibit amebic liver abscess in gerbils has been shown previously (9,10). However, the potential of 170CP to induce protective immunity is surprising, as previous studies have shown that high titers of serum immunoglobulin G anti- bodies to this fragment exacerbate amebic disease (10). Interestingly, analysis of antibody responses after oral infection with recombinant Yersinia cells indicated that the observed protection was most likely mediated by antibody-independent immune mechanisms, as antibody titers were relatively low compared to those from previous intraperitoneal vaccination trials with recombinant ameba lectin (10) and there was no correlation between the degree of protection and titers of antibodies (Fig.…”

The Bernhard Nocht Institute: 100 years of tropical medicine in Hamburg

“…In vitro diagnostic tests have been developed to discriminate infection by pathogenic amoebae from infection by non-pathogenic amoebae. A possible candidate antigen for a vaccine has been identified (Lotter et al 1997).…”