Exposure of neutralizing epitopes in the carboxyl-terminal domain of TcdB is altered by a proximal hypervariable region.

The sequence, activity, and antigenicity of TcdB varies between different strains of Clostridium difficile. As a result, ribotype-specific forms of TcdB exhibit different toxicities and are not strongly cross-neutralized. Using a combination of biochemical and immunological approaches, we compared two important variants of TcdB (TcdB012 and TcdB027) to identify the mechanisms through which sequence differences alter epitopes and activity of the toxin.