A RECOMBINANT ESCHERICHIA-COLI HEAT-STABLE ENTEROTOXIN B(STB) FUSION PROTEIN ELICITING NEUTRALIZING ANTIBODIES

STb is a heat-stable enterotoxin elaborated by enterotoxigenic Escheri chia coli strains associated with weaning piglets and is responsible f or diarrhoea in those animals. The maltose binding protein (MBP) of E. coil was used as a carrier for STb, a poorly immunogenic molecule. Co nstructions were produced where the gene coding for mature STD toxin ( MBP-STb) and a fragment of the gene spanning the major epitopic region of STb (AA8-AA30) (MBP-STb2) were fused to malE gene coding for MBP. The fusion proteins accumulated in the periplasm and were detected wit h a polyclonal antibody raised against the purified toxin. MBP-STb ind uced secretion in the biological model whereas MBP-STb2 was non-toxic. Immunization of rabbits evoked an antibody response to STb for these two fusion proteins. However, only MBP-STb elicited antibodies that ef fectively neutralized the toxicity of pure STb toxin as determined in the rat loop assay.