Stat6 is required for the actions of IL-4 on B and T lymphocytes. Stat6-deficient B lymphocytes have low proliferative capacity in response to IL-4 and submitogenic doses of anti-IgM antibody. Upregulation of the major histocompatibility complex (MHC) class II, as well as the low-affinity IgE receptor CD23, was abolished in response to IL-4 in the absence of Stat6. In T lymphocytes, Stat6 was essential for IL-4-induced proliferation and CD4+ T-cell differentiation and production of Th2 cytokines. When challenged with nematode, production of Th2-associated cytokines such as IL-4, IL-5, and IL-10, as well as Th2-type immunoglobulins such as IgG1 and IgE, was profoundly reduced (34-36).

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