ORAL IMMUNIZATION WITH AN ATTENUATED VACCINE STRAIN OF SALMONELLA-TYPHIMURIUM EXPRESSING THE SERINE-RICH ENTAMOEBA-HISTOLYTICA PROTEIN INDUCES AN ANTIAMEBIC IMMUNE-RESPONSE AND PROTECTS GERBILS FROM AMEBIC LIVER-ABSCESS

Attenuated salmonellae represent attractive candidates for the deliver y of foreign antigens by oral vaccination. In this report, we describe the high-level expression of a recombinant fusion protein containing the serine-rich Entamoeba histolytica protein (SREHP), a protective an tigen derived from virulent amebae, and a bacterially derived maltose- binding protein (MBP) in an attenuated strain of Salmonella typhimuriu m. Mice and gerbils immunized with S. typhimurium expressing SREHP-MBP produced mucosal immunoglobulin A antiamebic antibodies and serum imm unoglobulin G antiamebic antibodies. Gerbils vaccinated with S. typhim urium SREHP-MBP were protected against amebic liver abscess, the most common extraintestinal complication of amebiasis. Our findings indicat e that the induction of mucosal and immune responses to the amebic SRE HP antigen is dependent on the level of SREHP-MBP expression in S. typ himurium and establish that oral vaccination with SREHP can produce pr otective immunity to invasive amebiasis.