NONSPECIFIC-BINDING OF CLOSTRIDIUM-DIFFICILE TOXIN-A TO MURINE IMMUNOGLOBULINS OCCURS VIA THE FAB COMPONENT

Clostridium difficile toxin A binds nonspecifically to a mouse monoclo nal antibody (MAb) immunoglobulin G3 lambda chain [IgG3(lambda)], thro ugh the Fab component. This binding, which is retained even after boil ing the MAb, is temperature dependent, with more toxin bound at 4 than 37 degrees C (P = 0.0024), The nonspecific binding was decreased by i ncubation 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 th e Bandeiraea simplicifolia lectin BS-1, indicating that a terminal alp ha-galactose may not be involved, Binding was also not affected by com petitive assays with Lewis X antigen. The dependence on carbohydrate m oieties in nonspecific binding was also shown for two other MAbs, IgA( kappa) and IgM(lambda), with demonstration of a significant reduction in binding,vith a-galactosidase (P = 0.0001 and 0.0002, respectively) but not beta-galactosidase (P = 0.27 and 0.25, respectively).