Response of mouse intestinal loop to botulinum C2 toxin: enterotoxic activity induced by cooperation of nonlinked protein components

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Abstract
Botulinum C2 toxin, which is composed of 2 nonlinked protein components, components I and II, induced fluid accumulation in mouse intestinal loops. The secretory response to C2 toxin was initiated after a lag period of 1-2 h and increased gradually for at least 10 h. The activity of C2 toxin was enhanced by treatment with trypsin and abolished by neutralization with anti-component I or anti-component II sera. Neither component I nor component II alone induced the fluid accumulation in intestinal loops. The intestinal loop activity was demonstrated with the culture supernatants of strains of Clostridium botulinum types C and D that produced C2 toxin, but not with culture supernatants of strains that did not. None of the botulinum type A-F neurotoxins induced fluid accumulation in mouse intestinal loops. In addition to lethal and vascular permeability activities, C2 toxin thus has an enterotoxic activity for which the cooperation of components I and II is necessary. The fluid accumulation in intestinal loops inoculated with C2 toxin was not diminished by removal of the toxin from the loops. The secretory response was positive when intestinal lumina were exposed to component II followed by the removal of the component and inoculation with component I; it was negative when the intestinal lumina were exposed to component I followed by the removal of the component and inoculation with component II. Apparently, the secretory response of mouse intestinal loops to C2 toxin is induced by the binding of component II to the epithelial cell surfaces of the intestines and the consequent binding or penetration of component I into the cells.