Comparison of in silico and in vitro instantaneous velocity data. (A) Dotted trace: a leukocyte rolling on P-selectin in vitro as reported in . Gray, shaded traces: two simulations of a LEUKOCYTE ROLLING on PSELECTIN using ENVIRONMENT parameter values from Table 5 (part I-C). Both traces show fluctuating rolling velocities similar to the dotted trace. (B) Distance-time plots from the experiments in A; solid line: in vitro leukocyte (calculated from the reported instantaneous velocity data); circles: the two in silico LEUKOCYTES from A.