Nonspecific binding of Clostridium difficile toxin A to murine immunoglobulins occurs via the fab component.
Clostridium difficile toxin A binds nonspecifically to a mouse monoclonal antibody (MAb) immunoglobulin G3 lambda chain [IgG3(lambda)], through the Fab component. This binding, which is retained even after boiling the MAb, is temperature dependent, with more toxin bound at 4 than 37 degrees C (P = 0.0024). The nonspecific binding was decreased by incubation of the IgG3 lambda MAb with alpha- or beta-galactosidase (P = 0.0001 and 0.029, respectively), indicating that toxin A binds to a carbohydrate moiety on the Fab. However, binding was not blocked by the Bandeiraea simplicifolia lectin BS-1, indicating that a terminal alpha-galactose may not be involved. Binding was also not affected by competitive assays with Lewis X antigen. The dependence on carbohydrate moieties in nonspecific binding was also shown for two other MAbs, IgA(kappa) and IgM(lambda), with demonstration of a significant reduction in binding with alpha-galactosidase (P = 0.0001 and 0.0002, respectively) but not beta-galactosidase (P = 0.27 and 0.25, respectively).
Cooke
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DL
Microbial Pathogenicity Research Group, Institute of Infections and Immunity Queens Medical Centre, Nottingham, United Kingdom.
Borriello
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SP
D000818:Animals; D000911:Antibodies, Monoclonal / Q000378:metabolism; D001427:Bacterial Toxins; D004768:Enterotoxins / Q000378:metabolism*; D007140:Immunoglobulin Fab Fragments / Q000378:metabolism*; D007074:Immunoglobulin G / Q000378:metabolism*; D007146:Immunoglobulin lambda-Chains / Q000378:metabolism; D051379:Mice; D000519:alpha-Galactosidase / Q000494:pharmacology; D001616:beta-Galactosidase / Q000494:pharmacology
D000911:Antibodies, Monoclonal; D001427:Bacterial Toxins; D004768:Enterotoxins; D007140:Immunoglobulin Fab Fragments; D007074:Immunoglobulin G; D007146:Immunoglobulin lambda-Chains; C041348:tcdA protein, Clostridium difficile; D000519:alpha-Galactosidase; D001616:beta-Galactosidase