The Inhibitory Effect of Cholera Toxin B Subunit on <i>Clostridium Perfringens</i> Iota-Toxin-Induced Cytotoxicity

Abstract

Clostridium perfringens iota-toxin consists of an enzymatic Ia component and binding Ib component. Ib binds to membrane receptors, forms heptamers in lipid rafts, and associates with Ia. The toxin complex is internalized into cells. In this study, we evaluated the inhibitory effects of cholera toxin B subunit (CTB), which binds to lipid rafts, on iota-toxin-mediated cytotoxicity. We examined the effect of CTB on iota-toxin-induced cell rounding activity against MDCK (Madin-Darby canine kidney) cells and Ib-induced cell death in A431 (human epithelial) cells. The presence of CTB inhibited both the cell rounding activity of iota-toxin (MDCK cells) and Ib-induced cell death (A431 cells). Moreover, CTB blocked binding of the Ib monomer to both cells at 4°C. We found by immunofluorescence microscopy that, after loading with Ib and CTB at 4°C, Ib and CTB bound to distinct regions in the plasma membranes. In MDCK cells at 37°C, Ib internalized and partially coexisted with CTB in cytoplasmic vesicles. These findings demonstrated that CTB blocks the binding of iota-toxin to target cells. CTB may provide a protective effect against infection.