Porcine regulatory T cells: Mechanisms and T-cell targets of suppression

Tregs are known for their suppressive capacity on various immune reactions. In swine, existence as well as suppressive activity of Foxp3+ Tregs could be demonstrated but detailed functional investigations are lacking. Therefore, we analysed the functional properties of porcine Tregs. We observed that besides TCR stimulation Tregs require IL-2 for activation. Furthermore, we investigated the following mechanisms of suppression: (i) cell–cell contact dependency, (ii) production of soluble suppressive factors and (iii) competition for growth factors. Our experiments revealed that suppression by porcine Tregs is abrogated by blocking cell–cell contact or by supplementing excessive amounts of IL-2. Additionally it could be shown that porcine Tregs produce immunosuppressive IL-10. Thereby, we demonstrated that porcine Tregs can use all main mechanisms of suppression mentioned above. Further investigations on the suppressive activity of Tregs using CFSE proliferation assays demonstrated that suppression affects T-helper cells as well as cytotoxic T lymphocytes and TCR-γδ T cells.