Immunoprophylactic potential of cloned Shiga toxin 2 B subunit.

The Shiga toxins Stx1 and Stx2 contribute to the development of enterohemorrhagic O157:H7 Escherichia coli-mediated colitis and hemolytic-uremic syndrome in humans. The Stx2 B subunit, which binds to globotriaosylceramide (GB3) receptors on target cells, was cloned. This involved replacing the Stx2 B subunit leader peptide nucleotide sequences with those from the Stx1 B subunit. The construct was expressed in the TOPP3 E. coli strain. The Stx2 B subunits from this strain assembled into a pentamer and bound to a GB3 receptor analogue. The cloned Stx2 B subunit was not cytotoxic to Vero cells or apoptogenic in Burkitt's lymphoma cells. Although their immune response to the Stx2 B subunit was variable, rabbits that developed Stx2 B subunit-specific antibodies, as determined by immunoblot and in vitro cytotoxicity neutralization assays, survived a challenge with Stx2 holotoxin. This is thought to be the first demonstration of the immunoprophylactic potential of the Stx2 B subunit.