Nasal immunization with E-coli verotoxin 1 (VT1)-B subunit and a nontoxic mutant of cholera toxin elicits serum neutralizing antibodies

Escherichia coli O157:H7 produces two forms of verotoxin (VT), VT1 and VT2, which cause hemorrhagic colitis with development, in some cases, of hemoly tic uremic syndrome. These toxins consist of an enzymatically active A subu nit and pentamers of B subunit responsible for their binding to host cells. We used the secretion-expression system of Bacillus brevis to produce reco mbinant VT1B and VT2B. The secreted B subunits were purified and sequenced to verify their structure. Receptor-binding showed that rVT1B but not rVT2B bound to Gb3-receptor. When mice were nasally immunized with rVT1B or rVT2 B together with a nontoxic mutant of cholera toxin (mCT) or native cholera toxin (nCT) as adjuvants, serum IgG and mucosal IgA antibody responses to V T1B were induced. The VT1B-specific antibodies prevented VT1B binding to it s Gb3 receptor. In contrast, poor serum and no mucosal VT1B-specific antibo dies but brisk CTB-specific antibody responses were induced by nasal immuni zation with rVT2B in the presence of mCT or nCT. These results show that na sal immunization with rVTB and mCT as a nontoxic mucosal adjuvant is an eff ective regimen for the induction of VT1B but not VT2B antibody responses wh ich inhibit VT1B binding to Gb3 receptor. (C) 2001 Elsevier Science Ltd. Al l rights reserved.