STABILITY OF T(H)1 AND T(H)2 POPULATIONS

Using an in vitro model for the development of IFN-gamma-producing (T(h)1) and IL-4-producing (T(h)2) cells from CD4(+) T lymphocytes expressing a transgenic TCR, we show that IL-12 and IL-4 are the most potent stimuli for the differentiation of naive T cells to effector populations. When combinations of cytokines are present during T cell priming, the effect of IL-4 is dominant. Furthermore, differentiated T(h)1 cells can be converted into IL-4 producers by exposure to IL-4, but the T(h)2 phenotype is not reversible. The stability of T(h)2 populations may limit the ability to regulate T(h)2-dominant responses in pathologic situations.