Differentiated CD4+ T-cells produce a restricted set of cytokines, allowing their subdivision into two discrete populations: T-helper 1 (Th1), characterized by secretion of interleukin 2 (IL-2) and interferon γ (IFN-γ); and Th2, selectively producing IL-4, IL-5, and IL-10 (1 ). Polarized subsets of antigen(Ag)- specific CD4+ Th1 and Th2 cells can be induced in vivo by Ag priming, and their development is primarily influenced by the cytokine milieu during the initial phase of the immune response. Among cytokines, decisive roles are played by IL-12 and IL-4, driving T-cell responses toward the Th1 or Th2 phenotype, respectively (2 , 3 ). The polarization in Th1 and Th2 cells is also influenced by several other factors, including non-major histocompatibility complex (MHC) genetic polymorphism (4 -6 ; see Note 1 ), ligand-T-cell receptor (TCR) interaction (7 ,8 ), Ag dose (9 ,10 ), and mode of Ag administration (11 ; see Note 2 ).