MUCOSAL IMMUNOGENICITY OF A HOLOTOXIN-LIKE MOLECULE CONTAINING THE SERINE-RICH ENTAMOEBA-HISTOLYTICA PROTEIN (SREHP) FUSED TO THE A(2) DOMAIN OF CHOLERA-TOXIN

One strategy for the induction of mucosal immune responses by oral imm unization is to administer the antigen in conjunction with cholera tox in, Cholera toxin consists of one A polypeptide (CTA) which is noncova lently linked to five B subunits (CTB) via the A(2) portion of the A s ubunit (CTA(2)), Coupling of antigens to the nontoxic B subunit of cho lera toxin may improve the immunogenicity of antigens by targeting the m to GM1 ganglioside on M cells and intestinal epithelial cells. Here, we describe the construction of a translational fusion protein contai ning the serine-rich Entamoeba histolytica protein (SREHP), a protecti ve amebic antigen, fused to a maltose binding protein (MBP) and to CTA (2). When coexpressed in Escherichia coli with the CTB gene, these pro teins assembled into a holotoxin-like chimera containing MBP-SREHP-CTA (2) and CTB. This holotoxin-like chimera (SREHP-H) inhibited the bindi ng of cholera toxin to GM1 ganglioside, Oral vaccination of mice with SREHP-H induced mucosal immunoglobulin A (IgA) and serum IgG antiamebi c antibodies and low levels of mucosal anti-CTB antibodies, Our studie s confirm that the genetic coupling of antigens to CTA(2) and their co expression in E. coli can produce holotoxin-like molecules that are mu cosally immunogenic without the requirement for supplemental cholera t oxin, and they establish the SREHP-H protein as a candidate for evalua tion as a vaccine to prevent amebiasis.