Steady state cell surface complexes determine NK cell recruitment to the cell cycle.

<p><b>A</b>. Surface IL-15/IL-15R complex numbers were calculated from model simulations for IL-15 concentrations of 9, 25, 50, and 75 ng/ml and were plotted for <i>t</i> hours. The arrow represents increasing IL-15 concentration. <b>B–E</b>. The cell cycle threshold (generated <i>C_s</i> from the immediate affinity model) is used to predict the fraction of NK cells recruited to divide at various times. The model predictions (solid lines) are compared with results generated from independent experiments (filled circles) where IL-15 concentrations were 9 ng/ml (<b>B</b>, n = 3), 25 ng/ml (<b>C</b>, n = 4), 50 ng/ml (<b>D</b>, n = 2), and 75 ng/ml (<b>E</b>, n = 3). The quality of prediction is represented by the normalized root mean squared deviation (NRMSD). The NRMSD of model prediction vs. experimental data are shown as percentages in the upper left of each graph. For reference, linear regression was performed for all four sets of experimental data, and the NRMSD values of the linear regressions were 12% (9 ng/ml), 5% (25 ng/ml), 19% (50 ng/ml), and 9% (75 ng/ml).