The study investigates the role of the interleukin-2 receptor γ chain (IL-2Rγ) in cytokine receptor systems. IL-2Rγ is a necessary component of functional IL-2 receptors and is associated with X-linked severe combined immunodeficiency (XSCID) in humans. The research shows that IL-2Rγ physically associates with the interleukin-7 receptor (IL-7R) through chemical cross-linking experiments. This association enhances both the binding affinity and internalization efficiency of IL-7. The findings suggest that IL-2Rγ is part of more than one cytokine receptor system, including the IL-2 and IL-7 receptors. The study also demonstrates that IL-2Rγ increases the binding affinity of IL-7 and is essential for its internalization. These results provide insights into the defects observed in XSCID, particularly the T cell and B cell deficiencies. The authors propose that IL-2Rγ be designated as the common γ chain (γc) to reflect its role in multiple cytokine receptor systems.The study investigates the role of the interleukin-2 receptor γ chain (IL-2Rγ) in cytokine receptor systems. IL-2Rγ is a necessary component of functional IL-2 receptors and is associated with X-linked severe combined immunodeficiency (XSCID) in humans. The research shows that IL-2Rγ physically associates with the interleukin-7 receptor (IL-7R) through chemical cross-linking experiments. This association enhances both the binding affinity and internalization efficiency of IL-7. The findings suggest that IL-2Rγ is part of more than one cytokine receptor system, including the IL-2 and IL-7 receptors. The study also demonstrates that IL-2Rγ increases the binding affinity of IL-7 and is essential for its internalization. These results provide insights into the defects observed in XSCID, particularly the T cell and B cell deficiencies. The authors propose that IL-2Rγ be designated as the common γ chain (γc) to reflect its role in multiple cytokine receptor systems.