Defensins and other antimicrobial peptides in inflammatory bowel disease.

Recently published studies presenting novel and relevant information on defensins and other antimicrobial peptides in Crohn's disease and ulcerative colitis are reviewed. Different clinical localizations of Crohn's disease are associated with different deficiencies in epithelial and leukocyte antimicrobial peptide expression. As compared with ulcerative colitis, Crohn's disease of the colon is characterized by an impaired induction of beta defensins, and antimicrobial antiproteases elafin and SLPI, as well as the cathelicidin LL37. The attenuated induction of beta defensins is linked to fewer gene copy numbers in this locus, which is associated with colonic but not ileal Crohn's disease. In contrast, ileal Crohn's disease patients are characterized by a reduced antibacterial activity and a specific reduction of ileal Paneth cell defensins. This decrease is independent of the grade of histological inflammation and cannot be found in inflammation controls. Thus, some of these defects can be explained either by direct or indirect genetic mechanisms and appear to be primary. Unlike ulcerative colitis, ileal and colonic Crohn's disease are characterized by localized deficiencies of antibacterial peptides. Understanding the precise molecular mechanisms of the defective antibacterial barrier function might provide new therapeutic directions.