The interplay between the duration of TCR and cytokine signaling determines T cell polarization

Development of Th1 and Th2 effector lymphocytes is driven primarily by IL-1 2 or IL-4, but is also influenced by the strength of antigenic stimulation. However, the mechanism by which TCR signaling contributes to T cell polari zation remains elusive. We show that in the presence of IL-12 a short TCR s timulation can lead to efficient Th1 polarization and IL-12 exerts its effe ct when present during, as well as after, TCR signaling. In contrast, Th2 p olarization requires a prolonged TCR stimulation and IL-4 is effective only when present during the period of TCR triggering. The simultaneous stimula tion by TCR and IL-4 is required to induce demethylation of IL-4 and IL-13 genes that accompanies the stochastic generation of Th2 cells producing eit her or both cytokines. Thus, the duration of TCR stimulation represents a c rucial parameter that influences the response to polarizing cytokines and t he acquisition of T cell effector functions.