Limiting γc expression differentially affects signaling via the interleukin (IL)-7 and IL-15 receptors

Abstract

X-linked severe combined immunodeficiency (SCID-X1) results from mutations in the IL2RG gene, which encodes the common gamma chain (γc) of the receptors for interleukin (IL)-2, 4, 7, 9, 15, and 21. Affected infants typically lack T and natural killer (NK) cells as a consequence of loss of signaling via the IL-7 receptor (IL-7R) and the IL-15R, respectively. In some infants, however, autologous NK cells are observed despite failure of T-cell ontogeny. The mechanisms by which mutations in γc differentially impact T- and NK-cell ontogeny remain incompletely understood. We used SCID-X1 patient–derived EBV-transformed B cells to test the hypothesis that the IL-15R–mediated signaling is preferentially retained as γc expression becomes limiting. Signal transduction via the IL-15R was readily detected in control EBV-transformed B cells, and via the IL-7R when modified to express IL-7Rα. Under the same experimental conditions, patient-derived EBV-transformed B cells expressing trace amounts of γc proved incapable of signal transduction via the IL-7R while retaining the capacity for signal transduction via the IL-15R. An equivalent result was obtained in ED-7R cells modified to express varying levels of γc. Collectively, these results confirm that signal transduction via the IL-15R, and hence NK ontogeny, is preferentially retained relative to the IL-7R as γc expression becomes limiting.