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-2R alpha is critical and determines IL-2 bindin g to the tripartite IL-2R complex. To extend our previous studies, whi ch demonstrated that IL-2 regulates IL-2R alpha expression in vitro, w e have analyzed expression in IL-2-deficient mice in vivo. As in contr ol animals, CD4(-)CD8(-) thymocytes and bone marrow-derived B220(+) pr e-B cells were IL-2R alpha positive. In contrast, activated lymph node and splenic CD4 T cells (CD4(+)CD69(+)) were found to be n-2R alpha n egative, whereas similar to 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 fr om 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 spe cifically CD4 T cells, IL-2 remains in vivo, as in vitro, the most cri tical cytokine controlling both IL-2R alpha expression and sensitivity to IL-2.