Physical migration limits of mono- and polymorphonuclear cell types in transwell filter assay. (A) Transmigration of different cell types through polycarbonate membranes of 5-, 3-, 1-, and 0.45-µm pore diameter after 20 h (HT/MT1, HT/wt, and MDA/MT1 cells), 5 h (T-blasts) or 3 h (PMN). The cell number in the bottom compartment was normalized to transmigration through 5-µm pores as 100% reference. Solid and dashed vertical lines represent the pore cross section at 90 and 99% inhibition, respectively, of migration for each cell type (black lines, mononuclear cells; gray area between black lines depicts a range of subtotal migration limits; red lines, PMN). Subtotal limits were reached at 7–10 µm² for tumor cells and T-blasts, and 4 µm² for PMNs; and absolute limits at 5 µm² for tumor cells and T-blasts and 1–2 µm² for PMNs (n = 3–5; means, SD). (B) Polycarbonate membranes with pore sizes ranging from 8 to 1 µm in diameter (top row). Representative images of nuclear deformation in transmigrating dual-color HT1080 cells and (C) PMNs during passage through pores of decreasing size. Filter membranes were fixed and, in C, stained as indicated (n = 2). Arrows, direction of transmigration. Bars: (B) 10 µm, (C) 5 µm.