Background
IL-2R is made up of three chains, a (CD25), B (CD122), and y (CD132), of which only the a-chain is specific for IL-2. Signaling takes place mainly via CD122. Activated T cells express the high affinity receptor composed of all three chains. However, cells other than T cells, such as monocytes, express functional CD122 and CD132 and have the ability to signal following ligation of the intermediate affinity receptor consisting of the heterodimer formed by (D122 and CD132. CD25 (a chain of the high-affinity IL-2 receptor) deficiency is an autosomal recessive disorder due to mutations in the IL2RA gene. T regulatory cells constitutively express CD25 and respond to IL-2 generated by T cells during an immune response for their immunoregulatory functions. CD25 deficiency results in a syndrome similar to IPEX with severe enteropathy, diabetes mellitus, autoimmune hemolytic anemia, eczema, and lymphoproliferation. Importantly, patients with CD25 deficiency exhibit several unique features not seen in IPEX, namely chronic herpetic viral infections and an increased susceptibility to infections.
