Interleukin 4 (IL-4) is an immunomodulatory cytokine that functions to induce naïve helper T cells to differentiate into type 2 T helper (Th2) cells.  Th2 cells subsequently produce more IL-4 in a positive feedback loop.  IL-4 also promotes immunoglobulin IgG to IgE isotype switching on B cells.  IL-4 binds the IL-4Rα receptor to activate STAT6 signaling. 

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