The
interleukin 4 (
IL4) is a
cytokine that induces differentiation of naive helper T cells (
Th0 cells) to
Th2 cells. Upon activation by IL-4,
Th2 cells subsequently produce additional IL-4 in a positive feedback loop. The cell that initially produces IL-4, thus inducing Th0 differentiation, has not been identified, but recent studies suggest that basophils may be the effector cell. It is closely related and has functions similar to
Interleukin 13.