Induction of migration but not adhesion requires previous contact with Fn. (A) Time course of induction of horizontal migration (□), migration on tilted surface (), or adhesion (▪). Ten thousand FDCP-mix cells were assayed as described in Materials and Methods on plates precoated with Fn (10 μg/cm2 ) and in 100 U/mL IL-3. Values are means ± SD from triplicate experiments. Absolute values of the maximum responses were: Migration on horizontal surface, 85 ± 8%; migration on tilted surface, 46 ± 4 per field; adhesion, 57 ± 9%. (B and C) Previous contact on Fn and plate tilting are required to induce migration, independently of cytokine concentration in the culture medium. Ten thousand FDCP-mix cells were inoculated into 96-well plates precoated with Fn, and incubated in the presence of 100 U/mL IL-3 in a horizontal position and tilted at time point zero (B), or kept at a tilted position from the start of the experiment in the presence of 100 U/mL IL-3 from time point zero or 4 hours as indicated (C). Results in (B) and (C) are given as migrating cells analyzed by video imaging at 100× original magnification. Results represent means ± SD of triplicate determinations.