Fig. 1.

Diversification of naïve CD4 + T helper cells into various effector T helper cell lineages. Upon antigenic stimulation, naïve CD4 + T cells can be differentiated into diverse T helper cell subsets like Th1, Th2, Th17 and Treg. From in vitro and in vivo studies, instructive cytokines and transcription factors which are specific for each effector lineage were identified. In the early initiation stage, the unique signal transducer and activator of transcription (STAT) is activated by the environmental cytokine signals which leads to induction of lineage master regulators. Transcription factors from each distinct subset activate and control the various downstream genes and this mechanism is further enhanced and stabilizes the lineage commitment with epigenetic modification by specific stimuli and the action of transcription factors. As a result, effector cytokines and modulators can be released from each CD4 + T helper cell subsets and these further regulate immune responses accordingly to antigens.