Reduced a-defensin expression is associated with inflammation and not NOD2 mutation status in ileal Crohn’s disease

Revised 13 February 2008 Accepted 19 February 2008 Published Online First 27 February 2008 ABSTRACT Background and aims: Reduced ileal Paneth cell adefensin expression has been reported to be associated with Crohn’s disease, especially in patients carrying NOD2 mutations. The aim of this study was to independently assess whether NOD2, a-defensins and Crohn’s disease are linked. Methods: Using quantitative real-time polymerase chain reaction (RT-PCR), we measured the mRNA expression levels of key Paneth cell antimicrobial peptides (DEFA5, DEFA6, LYZ, PLA2G2A), inflammatory cytokines [interkelukin 6 (IL6) and IL8], and a marker of epithelial cell content, villin (VIL1) in 106 samples from both affected ileum (inflamed Crohn’s disease cases, n = 44) and unaffected ileum (non-inflamed; Crohn’s disease cases, n = 51 and controls, n = 11). Anti-human defensin 5 (HD5) and haematoxylin/eosin immunohistochemical staining was performed on parallel sections from NOD2 wild-type and NOD2 mutant ileal Crohn’s disease tissue. Results: In Crohn’s disease patients, DEFA5 and DEFA6 mRNA expression levels were 1.9and 2.2-fold lower, respectively, in histologically confirmed inflamed ileal mucosa after adjustment for confounders (DEFA5, p,0.001; DEFA6, p = 0.001). In contrast to previous studies, we found no significant association between adefensin expression and NOD2 genotype. HD-5 protein data supports these RNA findings. The reduction in HD-5 protein expression appears due to surface epithelial cell loss and reduced Paneth cell numbers as a consequence of tissue damage. Conclusions: Reduction in a-defensin expression is independent of NOD2 status and is due to loss of surface epithelium as a consequence of inflammatory changes rather than being the inciting event prior to inflammation in ileal Crohn’s disease.