The enteric protozoan Entamoeba histolytica is a major cause of morbidity and mortality worldwide. In general, transmission of infection and resultant amebic colitis and liver abscess is due to poor sanitary conditions, there is no vaccine available. By defining the mechanisms of parasite and lysis of tissue and the human immune response, substantial progress is vaccine development has occurred. Both humoral and cell- mediated mechanisms are operative in protection against amebic liver abscess. The role of mucosal immunity in a relevant model of intestinal amebiasis has not been defined. A parasite 260kDa galactose-inhibitable adherence protein (GIAP) mediates binding of trophozoites to colonic mucins, epithelial cells and host inflammatory cells. GIAP binding is required for the CA ++ dependent lysis of host tissues by E. histolytica. The GIAP consists of a 170kDa heavy subunit and a 35kDa light subunit, the heavy subunit is antigenic and possesses carbohydrate binding activity. Purified native GIAP is highly efficacious as a vaccine in the gerbil model of amebic livery abscess; the gene from the GIAP heavy subunit has been cloned and sequenced. Patients cured of invasive amebiasis possess salivary sIgA to the GIAP. The objectives of this proposal are: 1) to define the role of mucosal anti-GIAP secretory IgA (sIgA) in immunity intestinal amebiasis; 2) to construct a recombinant GIAP subunit vaccine effective in primate models of intestinal amebiasis and amebic liver abscess; 3) to determine if use of selected E. histolytica recombinant antigens in combination with GIAP subunits will enhance vaccine efficacy.
The specific aims and methods of this proposal are: 1) to define the sIgA response to the GIAP heavy subunit in human infection and experimental intestinal amebiasis in the baboon by ELISA assay of salivary and intestinal secretions; 2) to identify which portions of the GIAP heavy subunit elicit protective sIgA responses by production of adherence- inhibitory IgA monoclonal antibodies to may the heavy subunit, immunization of mice with selected GIAP subunits with assay of sIgA responses, and passive immunization of baboons with IgA monoclonal antibodies and active immunization of baboons with recombinant GIAP subunits to determine protection against experimental intestinal amebiasis; and 3) to determine in the baboon and gerbil models of experimental intestinal and liver amebiasis the efficacy of a recombinant amebiasis subunit vaccine containing GIAP subunits and the major cysteine proteinase or the liver abscess specific 29kDa surface antigen. Previous studies and preliminary data indicate that the proposed studies will greatly enhance our understanding of mucosal immunity to E. histolytica and lead to development of an effective amebiasis subunit vaccine.
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