Escherichia coli O157:H7 produces Stx1 and Stx2 causing severe diseases. Their B subunits (StxBs) are useful for a vaccine but exhibit low immunogenicity, especially Stx2B. Nasal vaccination with StxBs plus cholera toxin induces only serum anti-Stx1B antibodies in mice. However, nasal administration of a mutant of E. coli enterotoxin and His-tagged Stx2B induced serum antibodies neutralizing Stx2 in vitro or in vivo and mucosal IgA antibodies in lungs. As His-tagged Stx2B showed five or three polymers in gel filtration chromatography, His-tagged Stx2B forms smaller tertiary structure than the native one and is effective for preventing Stx2 toxemia as a nasal vaccine.
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