Protection of gerbils from amebic liver abscess by immunization with a recombinant protein derived from the 170kilodalton surface adhesin of Entamoeba histolytica. Infect. Immun

Amebiasis, infection by the intestinal protozoan parasite Entamoeba histolytica, is a leading parasitic cause of death. As a step in the development of a recombinant antigen vaccine to prevent E. histolytica infection, we looked at the ability of a recombinant version of the serine-rich E. histolytica protein (SREHP) to elicit a protective immune response against invasive amebic disease. Gerbils, a standard model for amebic liver abscess, were immunized with either a recombinant SREHP/maltose-binding protein (MBP) fusion, recombi-nant MBP alone, or phosphate-buffered saline (PBS), all combined with complete Freund's adjuvant. In the first trial (group 1), gerbils received a primary and two booster immunizations intraperitoneally; in the second trial (group 2), gerbils were immunized by a single intradermal injection. SREHP/MBP-immunized gerbils in both groups produced antibody to native SREHP and developed delayed-type hypersensitivity responses to recombinant SREHP. All gerbils were challenged by an intrahepatic injection with 5 X 10 ' virulent E. histolytica HM1:IMSS trophozoites. Complete protection from amebic liver abscess was seen in 64 % of the SREHP/MBP-immunized gerbils in group 1 and in 100 % of the SREHP/MBP-immunized gerbils in group 2. There was no protection observed in MBP- or PBS-immunized gerbils in either group. Our results indicate that the SREHP molecule has potential as a vaccine to prevent amebic infection and demonstrate that successful vaccination of animals with recombinant E. histolytica antigen vaccines is possible