Abstract
This work centered on the resolution of the paradox that even though a large number of receptors for Interleukin-2 (IL-2) are expressed on the cell surface of activated lymphocytes, only a small number of receptors bind IL-2 with high affinity and mediate proliferative signals. The working hypothesis proposed that the high affinity IL-2 receptor is actually a complex of subunit(s), with an unidentified limiting component. The association of the subunit(s), would confer high affinity ligand binding properties to the receptor. The experimental data support the initial hypothesis, and substantiate that the murine IL-2 receptor is composed of at least three subunits of p55 ($\alpha$), p75 ($\beta$) and p22 ($\gamma$). Expression of high affinity IL-2 receptors correlated with the detection of p55 and p75, each of which was shown to possess IL-2 binding capacity. The data further suggest that the murine IL-2 receptor may be comprised of additional subunits, namely p40, p100, p135 and p180.The apparent complexity of the murine IL-2 receptor system provides an excellent model and an opportunity to answer important questions in molecular and cellular immunology. Moreover, the better understanding of the molecular controls for cell growth in response to polypeptide growth factors such as IL-2 has obvious immediate repercussions for many areas of the basic and applied sciences.