3 - Monoclonal Antibodies and Immunodetection Methods for Vibrio cholerae and Escherichia coli Enterotoxins

Abstract

This chapter discusses the preparation of the monoclonal antibodies (MAbs) against cholera toxin (CT), and E. coli heat-labile enterotoxin (LT) of human (LTh) and porcine (LTp). Most of the MAbs produced has been directed against the B-subunit portion of the toxin molecules and were of the IgG or IgG 2 isotypes. Both MAbs against the B-subunit portion of the CT and LT had toxin-neutralizing capacity, whereas none of nine MAbs against the cholera A subunit had any detectable neutralizing ability. Of 70 anti-CT MAbs, no less than 44 reacted specifically with CT, the remaining ones showing full or partial cross-reactivity with LTs. Seven of the 25 MAbs against LTh reacted only with LTh, and five of 20 MAbs against LTp were LTp-specific. One MAb, which showed full cross-reactivity between CT, LT, and LTp, and one MAb that is specific for each of these toxins, are exploited for development of diagnostic LT detection methods based on the GM1-ELISA principle. These methods fulfilled the criteria of excellent sensitivity and specificity for the detection of any heat-labile toxin using the cross-reactive MAb, or for the detection of species-specific toxin using the unique epitope MAbs. By these methods, heat-labile enterotoxins are demonstrated in overnight cultures of fecal isolates; the sensitivity of the methods is further increased by inoculation of bacterial isolates or stools directly in GM1-coated microtiter plates.