The invention relates inter alia to a method for inducing a long-term protection in an animal against foreign antigens and tumor antigens comprising the step of administering to the animal at least one factor selected from type I interferons and Flt-3, and to a method for inducing a long-term increase of the number of dendritic cells in an animal comprising the step of administering to the animal a factor selected from type I interferon and Flt-3 and to a method of inducing or enhancing the maturation and/or for the activation of the immune system of an animal comprising the step of administering to the animal a factor selected from type I interferon and Flt-3.
