Isolation of B subunit-specific monoclonal antibody clones that strongly neutralize the toxicity of Shiga toxin 2.

Shiga toxin 2 (Stx2)-specific mAb-producing hybridoma clones were generated from mice. Because mice tend to produce small amounts of B subunit (Stx2B)-specific antibodies at the polyclonal antibody level after immunization via the parenteral route, mice were immunized intranasally with Stx2 toxoids with a mutant heat-labile enterotoxin as a mucosal adjuvant; 11 different hybridoma clones were obtained in two trials. Six of them were A subunit (Stx2A)-specific whereas five were Stx2B-specific antibody-producing clones. The in vitro neutralization activity of Stx2B-specific mAbs against Stx2 was greater than that of Stx2A-specific mAbs on HeLa229 cells. Furthermore, even at low concentrations two of the Stx2B-specific mAbs (45 and 75D9) completely inhibited receptor binding and showed in vivo neutralization activity against a fivefold median lethal dose of Stx2 in mice. In western blot analysis, these Stx2B-specific neutralization antibodies did not react to three different mutant forms of Stx2, each amino acid residue of which was associated with receptor binding. Additionally, the nucleotide sequences of the VH and VL regions of clones 45 and 75D9 were determined. Our Stx2B-specific mAbs may be new candidates for the development of mouse-human chimeric Stx2-neutralizing antibodies which have fewer adverse effects than animal antibodies for enterohemorrhagic Escherichia coli infection.
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