(A) Variation of time to reach [IL-2]max (τmax) with number of T cells and antigen dose. Data from six different experiments are plotted together. The grey plane is the best fits to the data, using partial least square regression in MATLAB. The fitting coefficients and standard error of mean for the experimental data are given. We find that the dependency with number of T cells and antigen dose for the time to reach [IL-2]max (τmax) is weak. We emphasize here that since the variation in duration for IL-2 production is very small, this cannot be a sufficient mechanism to establish the wide dynamic range of antigen dose scaling and population size-independence of IL-2 accumulation. (B) Left: parameterizing the basal rate of IL-2 production per cell. The apparent rate is estimated in molecules per second per cell, as with V being the reaction volume (V = 2.10−4 l), [IL-2] the measured concentration of IL-2 (in Molar) and Δt the time interval between measurements (expressed in seconds). Distribution of IL-2 secretion rates per cell at 8 hr after the start of co-culture for T cell populations of all sizes (105, 104, and 103 T cells per well) stimulated with a range of different antigen quantities (1 μM, 100 nM, 10 nM, and 1 nM K5). We estimated the basal rate of IL-2 production to be 7.5 molecules per cell per second. Right: parameterizing the rate acceleration for IL-2 production per cell. Maximal acceleration trajectory taken by 103 T cells stimulated with 1 μM K5. Error bars show standard error of mean of two replicates. Data is representative of four high time resolution experiments. We estimated the maximal boost in IL-2 secretion to be 30-fold over the basal rate of IL-2 secretion, hence 225 molecules per second per cell. (C) Parameterizing the upregulation of IL-2Rα, hours after the start of co-culture. Shown: single cell IL-2Rβ distributions for 105 5C.C7 T cells stimulated with 2.5 μM K5 antigen at 12, 24, 36, 48, 78, and 140 hr. Unstained control is shaded.