Control of IL-4 expression in T helper 1 and 2 cells.

The mechanism of differentiation of naïve T cells to a variety of effector lineages, but particularly to T helper type 1 (Th1) and Th2 cells, has been the subject of intense scrutiny over the past two decades. Studies have revealed that the expression of cytokines, receptors, signalling molecules, transcription factors, DNA methylating enzymes and histone-modifying enzymes is altered during the process and has been shown to play a co-ordinated role to facilitate expression of the cytokines interleukin-4 (IL-4), IL-5 and IL-13 in Th2 cells, or interferon-gamma in Th1 cells. Regulation of IL-4 expression has been of particular interest for two main reasons: first because IL-4 acts as a growth factor for Th2 cells, and second because of its role in the induction of immunoglobulin class switching to immunoglobulin E, which plays a critical role in mediating allergic responses. Study of the pathways that promote this tissue-restricted expression of IL-4 may highlight potential areas for therapeutic intervention.