Monoclonal antibodies with an expanded repertoire of specificities and potent neutralizing activity for Escherichia coli heat-labile enterotoxin.

Nine selected hybridoma cell lines that produced monoclonal antibodies against the heat-labile enterotoxin encoded by a plasmid from an Escherichia coli strain of human origin (LTh) were characterized. Hybridomas that produced anti-LTh antibodies with previously unrecognized specificities or reactivities were selected for cloning. Each monoclonal antibody was tested for isotype and for binding to LTh holotoxin, the A and B subunits derived from LTh (LTh-A and LTh-B), holotoxin encoded by a plasmid from an E. coli strain of porcine origin (LTp), and cholera enterotoxin (CT). Binding was also tested in Western blots with the following antigens: pentameric LTh-B, monomeric LTh-B, LTh-A, and the A1 and A2 fragments produced from LTh-A by treatment with trypsin. These monoclonal anti-LTh antibodies and selected anti-LTh and anti-CT monoclonal antibodies described previously were tested for neutralization of LTh, LTp, and CT. Five of the nine new monoclonal antibodies gave detectable cross-reactions with LTp and CT. Four reacted with determinants of LTh that were not present on CT; one of these four did not react with LTp and was specific for a unique epitope of LTh. Three antibodies were specific for LTh-B. All three reacted with pentameric LTh-B, but only one reacted in Western blots with monomeric LTh-B. Six antibodies were specific for LTh-A. Three reacted in Western blots with LTh-A and its A1 fragment; the other three did not react in Western blots. All nine of the new monoclonal antibodies neutralized LTh but not CT; the eight that cross-reacted with LTp in binding assays also neutralized LTp. Of four neutralizing anti-CT monoclonal antibodies that bound to LTh, none had significant neutralizing activity against LTh.