Abstract
There is consensus that inflammatory bowel diseases (IBDs) are the result of "dysregulated" immune reactivity towards commensal microorganisms in the intestine. This gut microbiome is clearly altered in IBD, but its primary or secondary role is still debated. The focus has shifted from adaptive to innate immunity, with its multitude of receptor molecules (Toll-like and NOD receptors) and antibacterial effector molecules (defensins, cathelicidin, and others). The latter appear to be at least partly deficient at different intestinal locations. Host genetics also support the notion that microbe-host interaction at the mucosa is the prime site of pathogenesis. In contrast, even the latest therapeutic antibodies are directed against secondary targets like cytokines and integrins identified decades ago. These so-called "biologicals" have disappointing long-term results, with the majority of patients not achieving remission in the long run. A promising approach is the development of novel drugs like defensin-derived molecules that substitute for the missing endogenous antibacterials.