FIGURE 2

The proliferative response of IL2R+ cell populations separated on the basis of IL2R density. Synchronized IL2R+ cells were labeled with anti-Tac (IL2R). Viable cells were selected for low or high IL2R expression via FACS. Flow cytometer analysis of IL2R expression is shown in the upper panels in linear plots of fluorescence intensity; (A) unseparated cells, (B) low IL2R+ subset, (C) high IL2R+ subset. After sorting, the different cell populations were cultured in the presence of immunoaffinity purified IL2 (0 pM - 250 pM). (D) Tritiated thymidine [³H-TdR] incorporation in response to a receptor-saturating IL2 concentration (250 pM) of unseparated cells (), low IL2R+ subset (), high IL2R+ subset (). (E) [³H-TdR] incorporation of the same cell populations as in (D), plotted as a function of IL2 concentration after 31 h of culture ¹³.