Cysteine Protease-Mediated Autocleavage of Toxins Regulates Their Proinflammatory Activity.

Background & Aims: toxin A (TcdA) and toxin toxin B (TcdB), the major virulence factors of the bacterium, cause intestinal tissue damage and inflammation. Although the 2 toxins are homologous and share a similar domain structure, TcdA is generally more inflammatory whereas TcdB is more cytotoxic. The functional domain of the toxins that govern the proinflammatory activities of the 2 toxins is unknown.

Methods: Here, we investigated toxin domain functions that regulate the proinflammatory activity of toxins. By using a mouse ilea loop model, human tissues, and immune cells, we examined the inflammatory responses to a series of chimeric toxins or toxin mutants deficient in specific domain functions.

Results: Blocking autoprocessing of TcdB by mutagenesis or chemical inhibition, while reducing cytotoxicity of the toxin, significantly enhanced its proinflammatory activities in the animal model. Furthermore, a noncleavable mutant TcdB was significantly more potent than the wild-type toxin in the induction of proinflammatory cytokines in human colonic tissues and immune cells.

Conclusions: In this study, we identified a novel mechanism of regulating the biological activities of toxins in that cysteine protease-mediated autoprocessing regulates toxins' proinflammatory activities. Our findings provide new insight into the pathogenesis of infection and the design of therapeutics against the disease.