In X-linked SCID caused by IL2RG deficiency, which immune cell populations are severely reduced?

In X-linked SCID caused by IL2RG deficiency, which immune cell populations are severely reduced?

• A. Only T cells are reduced
• B. T cells, B cells, and natural killer cells are severely reduced
• C. B cells only
• D. Natural killer cells only

Answer: (B)

A single defect in the common gamma chain blocks signaling from several interleukins that drive lymphoid development. The gamma chain is a shared component of receptors for IL-2, IL-4, IL-7, IL-9, IL-15, and IL-21. Signals through these cytokines are necessary for the maturation and function of different lymphocyte lineages: IL-7 is crucial for thymic T cell development, IL-15 supports natural killer (NK) cell maturation, and IL-4/IL-21 signaling plus T cell help influence B cell development and antibody responses. When the gamma chain is defective, signaling for these cytokines is lost, leading to very low numbers of T cells and NK cells. B cell development and function are also impaired due to disrupted IL-7 signaling and reduced T cell help, resulting in markedly decreased B cells as well. So, all three lymphocyte populations—T cells, B cells, and NK cells—are severely reduced in this condition.

A single defect in the common gamma chain blocks signaling from several interleukins that drive lymphoid development. The gamma chain is a shared component of receptors for IL-2, IL-4, IL-7, IL-9, IL-15, and IL-21. Signals through these cytokines are necessary for the maturation and function of different lymphocyte lineages: IL-7 is crucial for thymic T cell development, IL-15 supports natural killer (NK) cell maturation, and IL-4/IL-21 signaling plus T cell help influence B cell development and antibody responses. When the gamma chain is defective, signaling for these cytokines is lost, leading to very low numbers of T cells and NK cells. B cell development and function are also impaired due to disrupted IL-7 signaling and reduced T cell help, resulting in markedly decreased B cells as well. So, all three lymphocyte populations—T cells, B cells, and NK cells—are severely reduced in this condition.