Expression of the IL-2 receptor gamma subunit in resting human CD4 T lymphocytes: mRNA is constitutively transcribed and the protein stored as an intracellular component.

IL-2 receptor (IL-2R) is composed of three subunits named IL-2Ra, IL-2Rb and IL-2Rg. Here, we study the expression of the IL-2Rg in highly purified, resting peripheral human CD4 T lymphocytes. We show by FACS analysis that the IL-2Rg subunit is not detectable at the cell surface of peripheral CD4 T lymphocytes. This result has been verified after acid treatment of the cell surface and analysis with three specific anti-IL-2Rg mAb. Using RT-PCR and intracellular FACS analysis, we demonstrate that IL-2Rg is constitutively expressed at the mRNA level and the protein is stored as an intracellular component in resting CD4 T lymphocytes. IL-2Ra and b subunits are not detectable by these methods. In addition, we show that CD4 T cells remain insensitive to a variety of cytokines that share IL-2Rg as a common subunit of their receptors (e.g. IL-2, IL-4, IL-7 and IL-15). The kinetics of cell surface expression of IL-2Rg have been studied after activation of CD4 T lymphocytes and compared with induction of IL-2Ra and IL-2Rb. Maximum expression of IL-2Rg is observed after 2 days of stimulation, and remains constant and comparable to IL-2Rb up to day 5. We conclude from these studies that IL-2Rg is translocated to the membrane only after T cell activation and induction of the IL-2Ra and IL-2Rb genes. We hypothesize that in CD4 T cells a large intracellular pool of IL-2Rg is present but that its cell surface translocation depends on the expression of a and/or b chains specific for IL-2, IL-4, IL-7, IL-9 or IL-15.