In the present study we took advantage of a well-validated model of PSA, to selectively study the sole effector phase of allergy and exploited DEREG mice to address the role of constitutive Foxp3+ Treg and evaluate by transfer experiments the relative beneficial effect of constitutive versus allergen-specific Foxp3+ Treg on MC-mediated allergic symptoms. The gene discussed is FOXP3; the disease is Allergy.