To Örebro University

Background and aims: The aetiology of Crohn's disease is poorly understood. By investigating twin pairs discordant for Crohn's disease we aimed to assess if the dysregulated barrier represents a cause or a consequence of inflammation and to evaluate the impact of genetic predisposition on barrier function.

Methods: Ileal biopsies from 15 twin pairs discordant for Crohn's disease (monozygotic n=9, dizygotic n=6) and 10 external controls were mounted in Ussing chambers to assess paracellular permeability to51Chromium (Cr)-EDTA and trancellular passage to non-pathogenic E. coli K-12. Experiments were performed with and without provocation with acetylsalicylic acid. Immunofluorescence and ELISA were used to quantify the expression level of tight junction proteins.

Results: Healthy co-twins and affected twins displayed increased 51Cr-EDTA permeability at 120 min both with Acetylsalicylic acid (p<0.001) and without (p<0.001) when compared to controls. A significant increase in 51Cr-EDTA flux was seen already at 20 minutes in healthy monozygotic co-twins compared to controls (p≤0.05) when stratified by zygosity, but not in healthy dizygotic co-twins. No difference in E. coli passage was observed between groups. Immunofluorescence of the tight junction proteins claudin-5 and tricellulin showed lower levels in healthy co-twins (p<0.05) and affected twins (p<0.05) compared to external controls, while ELISA only showed lower tricellulin in Crohn's disease twins (p<0.05).

Conclusion: Our results suggest that barrier dysfunction is a primary defect in Crohn's disease, since changes were predominantly seen in healthy monozygotic co-twins. Passage of E. coli seems to be a consequence of inflammation rather than representing a primary defect.