NFKB1 and Cowden disease: Importantly, challenge of biopsies with Rifampicin did not significantly reduce the IL-8 or IL-1ß mRNA expression in the biopsies from control and quiescent CD patients (Fig 1A and 1B), indicating that outside the context of active IBD, PXR activity is not a rate-limiting factor with respect to NF-κB-directed gene expression.