Monoclonal antibodies against the enzymatic subunit of both pertussis and cholera toxins.

A synthetic peptide corresponding to amino acids 6-17 of the A subunit of pertussis toxin was synthesised and used for the immunization of Balb/c mice and the subsequent production of monoclonal antibodies (MAbs). This peptide contains a region of eight amino acids which is homologous to a region in the cholera toxin A subunit. The properties of two of the resultant MAbs are described. Both of the antibodies (CP7-3003F7, an IgG3 and CP7-3004G6X1, an IgG1) react in an ELISA with the peptide and with intact pertussis toxin, pertussis toxin A subunit and cholera toxin A subunit, but do not react significantly with pertussis toxin B subunit, intact cholera toxin, or cholera toxin B subunit. Competition ELISA assays in which the peptide, the intact toxins and the toxin subunits were compared with respect to their ability to inhibit the binding of the MAbs to peptide-coated ELISA plates demonstrated that only pertussis toxin A subunit was as active, on a molar basis, as the peptide. Western blot analyses of the holotoxins confirmed that both MAbs were reactive only with the toxin A subunits. The MAbs were unable to neutralize the activity of cholera toxin or pertussis toxin in a Chinese hamster ovary (CHO) cell assay. Both were also unable to neutralize either the ADP-ribosylation activity or the NAD-glycohydrolase activity of the pertussis toxin A subunit. The significance of these results with respect to the role of this conserved site in the activity of these two toxins is discussed.