The third subunit, the so-called common γ (γc) chain, of the IL-2 receptor is shared among the receptors for IL-2, IL-4, IL-7 and IL-15, and dysfunction of the γc chain is thought to cause X-linked severe combined immunodeficiency (XSCID) ascribed to impairment of early T cell development. However, cytokines linked to XSCID are as yet unidentified. A mAb specific for the γc chain, TUGm2, profoundly inhibited cell proliferation in response to IL-9. Another mAb, TUGm3, immunoprecipltated [125I]IL-9 cross-linked with either the IL-9 receptor or the γc chain. These results demonstrate that the γc chain is included in the functional receptor complex for IL-9, which was initially characterized as a T cell growth factor and is essential for IL-9-dependent growth signal transductlon.
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