Recombinant Human IL-4Interleukin-4 (IL-4) induces differentiation of naive helper T cells (Th0 cells) to Th2 cells. Upon activation by IL-4, Th2 cells subsequently produce additional IL-4. IL-4 has many biological roles, including the stimulation of activated B-cell and T-cell proliferation, and the differentiation of CD4 T-cells into Th2 cells. It is a key regulator in humoral and adaptive immunity. IL-4 induces B-cell class switching to IgE, and up-regulates MHC class II production. Overproduction of IL-4 is associated with allergies.