Enhanced immunogenicity of a novel Stx2Am-Stx1B fusion protein in a mice model of enterohemorrhagic Escherichia coli O157:H7 infection

Shiga toxins (Stxs) which include Stx1 and Stx2 produced by EHEC O157:H7 are responsible for severe diseases, including hemolytic uremic syndrome (HUS) in humans. In our previous study, a fusion protein Stx2B-Stx1B (2S for short) was prepared and displayed immunogenicity against low lethal dose challenge of E. coli O157:H7. To enhance the immunogenicity against both toxins above, we constructed a novel fusion protein carrying the Stx1B subunit and enzyme-inactive Stx2A subunit, designated Stx2Am-Stx1B (SAmB for short). The fusion protein SAmB elicited high level humoral IgG and IgG1 in mice and induced Th2-typical cytokines IL-4/IL-10 but not Th1-typical cytokine INF-γ, indicating a partial to humoral immunoresponse mediated by Th2-type cells that contributed to this humoral reactivity. Higher level neutralizing antibodies against Stx2 were elicited by SAmB than 2S. An enhanced effect of protection (93.3%) against high lethal dose challenge of lysed E. coli O157:H7 was observed, and the SAmB also provided cross protection against purified Stx1 and Stx2.