IL33 and clostridium difficile infection: By comparing the transcriptome of the entire cecal tissue of mice infected with the highly virulent CDT toxin-expressing C. difficile ribotype 027 strain R20291 or its attenuated isogenic mutant (lacking the CDTb receptor-binding region) with uninfected controls, Frisbee at al.141 also observed that IL-33 is upregulated in response to increasing severity of CDI.