Rationale: Natural and inducible regulatory T cells (Tregs) are key players in controlling the development of asthmatic inflammation. However, the role of these cells in the mechanisms leading to tolerance in an established model of asthma has not yet been defined.
Methods: To examine the respective role of these subsets in the induction of allergen specific tolerance in established asthma, BALB/c mice were sensitized to OVA, tolerized intranasally with OVA and depleted of CD25+ cells by intraperitoneal injection of anti-CD25 mAb (PC61) during tolerance induction. Mice were then challenged by OVA aerosols and efficiency of tolerization was evaluated. T cell subsets were characterized by flow cytometry. Their suppressor activity and proliferation were determined by in vitro coculture systems and by cell transfers experiments.
Results: Intranasal treatment with OVA led to a marked upregulation of CD4+CD25+ Foxp3+ T cells in the lungs. These cells were regulatory as shown by their suppressive and anergic characteristics in vitro. CD25+ T cells depletion severely hampered tolerance induction as indicated by a strong recruitment of eosinophils into BALF and a vigorous T cell response to OVA upon challenge, in contrast to non depleted mice. However, in vivo transfer of CD4+CD25+ T cells had no effect on lung inflammation whereas transfer of CD4+CD25- T cells led to reduced eosinophils recruitment upon challenge. PKH26 labeled CD4+CD25- T cells did not proliferate in vivo, although they did proliferate in vitro. When stimulated with OVA in vitro, CD4+CD25- T cells produced high amounts of IL-10, low IL-5 and no TGF-b, IL-17 or IFN-g. They were equally distributed in the spleen, BLN and lungs.
Conclusions: In conclusion, both CD4+CD25+ and CD4+CD25- T cells appear to be essential in tolerance induction. The functional relationship between both subsets will have to be further analyzed.