Interleukin 4 (IL-4) is a cytokine produced primarily by T-helper 2 (Th2) cells, but also by mast cells, basophils, and eosinophils. It plays a crucial role in the immune system, particularly in the differentiation of naive T cells into Th2 cells. IL-4 is involved in immune regulation and has significant effects on a variety of cell types.
