CD4+CD25+ T regulatory cells in IBD

Introduction: Intestinal immune responses are regulated by both specialized inflammatory and regulatory T cell (Treg) populations.

Aims: Based on previous results from our group, we now determine whether differences in the frequency of Treg or Treg subsets in peripheral blood of IBD patients can serve as a subclinical marker of disease activity and investigate basic mechanisms of the activation and suppressive function of Treg in IBD.

Methods: We established a combined staining of FOXP3 and CD25 which allows a more precise quantification of Treg by flow cytometry compared to gating on CD4+CD25high cells. In addition we analyzed the skin- and gut-homing potential of Treg in IBD patients and healthy controls. To establish a suppression system driven by bacterial antigen, we first generated optimal and controlled conditions on the site of the effector T cells, the bacterial antigen(s) and the regulatory T cells.

Results: In our clinical cohort, preliminary time course analyses identify individual patients who show a decrease of Treg frequency during active disease and an increase of Treg frequency in response to treatment and clinical improvement. Investigating Treg subtypes we could identify subsets with different homing potential within the CD25+FOXP3+ Treg. Treg expressing the skin homing marker CLA were more frequent compared to gut homing Treg which express integrin β7. Expression, however, was not significantly different between healthy donors and IBD patients and it was independent from IBD activity. We established a highly sensitive system consisting of CD4+ effector cells and antigen-pulsed dendritic cells which enables the analysis of an antigen-specific suppression by Treg.

Conclusions: Since our preliminary long term analysis demonstrates that the frequency of peripheral blood Treg fluctuates in individual IBD patients depending on their disease activity, the study will be extended to determine whether measurement of peripheral blood Treg can provide relevant information for the clinical management of IBD patients. Furthermore, we will investigate the suppressive function of Treg in antigen-specific systems to dissect a potentially insufficient stimulation of Treg in IBD patients after activation with enteric bacterial antigens.