title: Murine monoclonal antibodies neutralizing the cytotoxic activity of diphtheria toxin.
abstract: In this study, murine monoclonal antibodies that specifically bound to the A and B subunits of diphtheria toxin (DT) were produced by conventional hybridoma technology using the spleens of BALB/c mice immunized with diphtheria DTP vaccine and CRM197. Monoclonal antibodies specific to the A subunit, i.e. clone AC5, as well as those specific to the B subunit, i.e. clone BB7, could neutralize the DT-mediated cytotoxicity to Vero cells in microcultures. The DT neutralizing mechanisms have yet to be determined. The MAbBB7 is hypothesized to either interfere with the DT receptor binding or with the pore forming function of the T domain of the B subunit. The MAbAC5 could neutralize the DT mediated cytotoxicity when mixed with the DT before adding to the Vero cell culture thus suggesting that the antibody interfered with the translocation of the A subunit. The A subunit-antibody complex might be too large to pass through the membrane channel formed by the T domain and thus prevent the accessibility of the A subunit to the cytosolic target. It is also possible that the MAb AC5 blocked the enzymatic active site of the enzyme catalytic subunit. While further experiments are needed to localize the epitopes of the two MAbs on the holo-DT in order to reveal the DT neutralizing mechanisms, both MAbs in their humanized forms have a high potential as human therapeutic antibodies for diphtheria.
authors.affiliation: Faculty of Allied Health Sciences, Thammasat University, Pathum-thani, Thailand.
authors.forename: Kanchana
authors.initials: K
authors.lastname: Usuwanthim
authors.forename: Anek
authors.initials: A
authors.lastname: Pootong
authors.forename: Urai
authors.initials: U
authors.lastname: Chaisri
authors.forename: Pongsri
authors.initials: P
authors.lastname: Tongtawe
authors.forename: Pramuan
authors.initials: P
authors.lastname: Tapchaisri
authors.forename: Manas
authors.initials: M
authors.lastname: Chongsa-Nguan
authors.forename: Wanpen
authors.initials: W
authors.lastname: Chaicumpa
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology* / Q000378:metabolism; D002522:Chlorocebus aethiops; D004167:Diphtheria Toxin / Q000276:immunology* / Q000378:metabolism; D006825:Hybridomas; D051379:Mice; D008807:Mice, Inbred BALB C; D009500:Neutralization Tests; D010446:Peptide Fragments / Q000276:immunology* / Q000378:metabolism; D014709:Vero Cells
chemical_list: D000911:Antibodies, Monoclonal; D004167:Diphtheria Toxin; D010446:Peptide Fragments; C029795:diphtheria toxin fragment A; C039171:diphtheria toxin fragment B