Influence of inflammation and treatment on ileal and colonic antimicrobial defensin expression in active Crohn's disease

Aims: Crohn's Disease (CD) has been linked to different functional deficiencies of antimicrobial defensins. Ileal CD is characterized by reduced expression of α-defensins (HD5, HD6). The mechanism is a compromised WNT/Tcf4 stem cell differentiation pathway and -in some cases- a mutation in NOD2. Colonic CD is mediated by an attenuated induction of β-defensins (HBD2, HBD3) which is due to a gene copy number polymorphism. Herein, we aimed to address if current treatments of CD influence the defensin expression in clinical samples.

Methods: Biopsies were collected from inflamed CD tissue of the small (n=55) and large intestine (n=45). RNA expression levels from defensins (HD5, HD6, HBD1, HBD2, HBD3) and cytokines (Il1β, Il-6, Il-8, Il-10, ICAM1, TNF-α) were quantified by real-time RT-PCR with external standards. Samples were arranged into groups moderate or severe inflammation based on IL-8. After retrospective analysis we surrogated the samples according to the use of steroids (ileum n=31, colon n=24), azathioprine (ileum n=10, colon n=9) and 5-Asa (ileum n=16, colon n=15).

Results: In small intestinal CD patients neither steroids, nor azathioprine, nor 5Asa seemed to have any effect on α- and β- defensin expression. As reported earlier, the expression of Paneth cell α-defensins was independent of the degree of inflammation and did not correlate with Il-8. Similarly, in the colon, inducible β-defensin levels were unchanged with or without current treatments and equally expressed in all inflamed samples. As reported earlier, the constitutive β-defensin HBD1 was decreased in case of severe inflammation and seemed to be up regulated by steroids in this group (p=0.0087). Interestingly, the anti-inflammatory cytokine Il-10 showed a similar pattern with increased expression (p=0.0173) in severely inflamed tissue and steroid treatment.

Conclusions: As tested in a clinical setting using retro-perspective analysis of inflamed CD samples, the currently used standard treatment did not influence defensin expression. In addition, the degree of inflammation itself did not change the gene expression of antimicrobial Paneth cell defensins. Hopefully, additional future drugs aimed at restoring the host-microbe balance at the intestinal mucosa will be identified.