Introduction The Nuclear Factor kappa B (NFκB) family of five transcription factors signals via two pathways (classical and alternative). Classical pathway NFκB signalling has previously been implicated in the pathogenesis of inflammatory bowel diseases (IBD). However, the role of alternative NFκB pathway activation in the development of intestinal inflammation has not previously been investigated.

Aims To investigate the susceptibility of mice deficient in two individual NFκB family members to DSS-induced colitis and the associated molecular changes.

Methods Colitis was induced in adult male NFκB1-null and NFκB2-null mice and their wild-type (C57BL/6) counterparts by oral 2% DSS administration for 5 days (n=10 per group). Weight loss and Disease Activity Index (DAI) were evaluated daily. Animals were euthanased on day 6 and histological colitis severity was evaluated in H/E stained colonic sections. The colonic expression of 6 key pro-inflammatory cytokines (TNF-α, IL-1β, INF-γ, IL-6 and IL-14) was assessed by real time PCR (n=4 per group). Statistical comparisons were mostly performed by ANOVA with Bonferroni post-hoc tests, but the Kruskal–Wallis with Dunn's multiple comparison test was used to analyse DAI and histological scores.

Results After oral administration of 2% DSS, NFκB1-null mice showed significantly more loss of body weight whereas NFκB2-null mice showed significantly less loss of body weight on days 5 and 6 compared to wild-type mice. DAI was also significantly higher in NFκB1-null mice and significantly lower in NFκB2-null mice compared to C57BL/6 mice. In agreement with these clinical findings, histological assessment of DSS treated animals confirmed a severely damaged and inflamed distal colon in C57BL/6 and NFκB1-null mice and minimal histological damage and significantly lower inflammation scores in NFκB2-null mice. The expression of IL-6 mRNA was significantly increased in DSS-treated NFκB1-null colon and the expressions of TNF-α and IL-14 mRNAs were significantly reduced in DSS-treated NFκB2-null colon.

Conclusion Disruption of the classical NFκB signalling pathway by deleting NFκB1 exacerbates colonic inflammation and tissue damage following DSS administration which may be partially mediated by IL-6. This suggests that classical NFκB pathway inhibitors may be paradoxically harmful in IBD. However, disruption of the alternative pathway by deleting NFκB2 protected murine colon from developing inflammation and this was associated with reduced expression of TNF-α and IL-14. Pharmacological inhibition of the NFκB2 signalling pathway may therefore be a promising novel therapeutic strategy for IBD.

Competing interests None declared.