Th2 cell culture: Na•ve CD4 T cells (CD4+CD44lowCD62LhighCD25-) were purified from lymph node. Cells cultured in RPMI medium 1640 (Invitrogen) supplemented with 10% FBS (Hyclone), 200 mM Glutamine, 100 mM Sodium pyruvate (Gibco), 50__M __-mercaptoethanol (Sigma), 100 U/ml penicillin and 100 _g/ml streptomycin at 37_¡C in a humidified atmosphere of 5% CO2. a-IFN-g 10_g/ml, a-IL-12 10_g/ml, IL-4 5000U/ml. Na•ve CD4 T cells from Bcl11bfl/fl-CreERT2 mice cultured under Th2 conditions without 4-OHT for 4 days, 1 day resting, then an additional 4 days of Th2 conditions without 4-OHT