IL-2 receptor alpha-chain expression is independently regulated in primary and secondary lymphoid organs.

The IL-2R is composed of three chains: IL-2R alpha, IL-2R beta, and IL-2R gamma. In mice, IL-2Ra is critical and determines IL-2 binding to the tripartite IL-2R complex. To extend our previous studies, which demonstrated that IL-2 regulates IL-2R alpha expression in vitro, we have analyzed expression in IL-2-deficient mice in vivo. As in control animals, CD4- CD8- thymocytes and bone marrow-derived B220+ pre-B cells were IL-2R alpha positive. In contrast, activated lymph node and splenic CD4 T cells (CD4+ CD69+) were found to be IL-2R alpha negative, whereas approximately 20% of the same cell populations from the MLR/lpr strain, which also accumulate large numbers of CD4-activated T cells in the presence of intact IL-2, retained expression. A similar pattern of IL-2R alpha expression was found among splenic CD8 cells from IL-2(-/-) and IL-2(+/-) animals. These findings demonstrate that in primary lymphoid organs, IL-2 is not directly involved in IL-2R alpha expression. However, at the level of mature lymphocytes, and more specifically CD4 T cells, IL-2 remains in vivo, as in vitro, the most critical cytokine controlling both IL-2R alpha expression and sensitivity to IL-2.