Functional Role of Interleukin-4 (IL-4) and IL-7 in the Development of X-Linked Severe Combined Immunodeficiency

X-linked severe combined immunodeficiency (X-SCID) is characterized by an absent or diminished number of T cells and natural-killer (NK) cells with a normal or elevated number of B cells, and results from mutations of the γc chain. The γc chain is shared by interleukin-2 (IL-2), IL-4, IL-7, IL-9, and IL-15 receptors. Recently, a survival signal through the IL-7 receptor  (IL-7R) chain was shown to be important for T-cell development in mice and was suggested to contribute to the X-SCID phenotype. In the present study, we examined function of a mutant γc chain (A156V) isolated from an X-SCID patient and found that T cells expressing the mutant γc chain were selectively impaired in their responses to IL-4 or IL-7 compared with the wild-type γc chain expressing cells although responses to IL-2 or IL-15 were relatively maintained. The result shows that IL-4– and/or IL-7–induced signaling through the γc chain is critical for T-cell development and plays an important role in the development of the X-SCID phenotype.