Increase of regulatory T cells in ileal mucosa of untreated pediatric Crohn's disease patients

Abstract

Background. Inflammatory bowel disease (IBD) of pediatric and adult onset differs in several aspects although little knowledge exists about pathogenic disparity. Regulatory T cells (Tregs) characterized as CD4⁺CD25⁺Foxp3⁺ are modulators of gut homeostasis, but their role in human IBD remains unclear. Objective. To evaluate the mucosal distribution of Foxp3⁺ and CD25⁺ cells in untreated pediatric IBD patients at the time of diagnosis. Material and methods. Untreated pediatric (n = 14) and adult (n = 12) Crohn's disease (CD) patients were prospectively included together with age-matched symptomatic controls. Colonic and ileal mucosal biopsies collected at diagnosis were studied by immunohistochemistry for enumeration of T cells and for mucosal expression of Foxp3 and CD25. Multicolor immunofluorescence staining was performed in situ to phenotype Foxp3⁺ cells as Tregs and characterize the CD25⁺ cells. Results. The density of mucosal T cells displayed only small variations, while that of Foxp3⁺ cells and CD25⁺ cells was increased in CD patients. Multicolor immunofluorescence showed that most CD25⁺ cells were macrophages. Interestingly, in the ileum of pediatric CD patients the density of Foxp3⁺ cells was significantly higher than in adult CD patients. Co-expression of Foxp3 and CD25, as well as Foxp3 and CTLA-4, indicated that the Foxp3⁺ cells were Tregs. Conclusion. Mucosal numbers of Foxp3⁺ Tregs and activated (CD25⁺) macrophages are elevated in both pediatric and adult ileal CD. The greater increase of ileal Foxp3⁺ Tregs in pediatric CD than in adult CD might contribute to the relatively less frequent phenotype of isolated ileal enteritis in CD children.

Key Words::

• CD25
• Foxp3
• inflammatory bowel disease
• macrophages
• pediatrics

Acknowledgements

We thank Aaste Aursjø at LIIPAT for expert assistance with sectioning and immunostaining, Jorunn Brattlie at Oslo University Hospital Rikshospitalet for general technical support, Gunn Seim Ekeland at Akershus University Hospital for administrative assistance, and members of the IBSEN II study group for the recruitment of patients and specimens. The study has been supported by the Norwegian Cancer Society, the Research Council of Norway, and research grants of South-Eastern Norway Regional Health Authority.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.