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, recombinant 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 SHEHP and developed 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 SHEHP/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.