PROTECTION OF GERBILS FROM AMEBIC LIVER-ABSCESS BY IMMUNIZATION WITH A RECOMBINANT ENTAMOEBA-HISTOLYTICA ANTIGEN

Amebiasis, infection by the intestinal protozoan parasite Entamoeba hi stolytica, is a leading parasitic cause of death. As a step in the dev elopment of a recombinant antigen vaccine to prevent E. histolytica in fection, we looked at the ability of a recombinant version of the seri ne-rich E. histolytica protein (SREHP) to elicit a protective immune r esponse against invasive amebic disease. Gerbils, a standard model for amebic liver abscess, were immunized with either a recombinant SREHP/ maltose-binding protein (MBP) fusion, recombinant MBP alone, or phosph ate-buffered saline (PBS), all combined with complete Freund's adjuvan t. In the first trial (group 1), gerbils received a primary and two bo oster immunizations intraperitoneally; in the second trial (group 2), gerbils were immunized by a single intradermal injection. SREHP/MBP-im munized gerbils in both groups produced antibody to native SREHP and d eveloped delayed-type hypersensitivity responses to recombinant SREHP. All gerbils were challenged by an intrahepatic injection with 5 X 10( 4) virulent E. histolytica HM1:IMSS trophozoites. Complete protection from amebic liver abscess was seen in 64% of the SREHP/MBP-immunized g erbils in group 1 and in 100% of the SREHP/MBP-immunized gerbils in gr oup 2. There was no protection observed in MBP- or PBS-immunized gerbi ls in either group. Our results indicate that the SREHP molecule has p otential as a vaccine to prevent amebic infection and demonstrate that successful vaccination of animals with recombinant E. histolytica ant igen vaccines is possible.