Morphology of PMNs at different stages of transendothelial migration.

PMNs can be identified under either phase-contrast (A) or scanning electron microscopy (B-D). (A) and (B) show several transmigrating PMNs (arrowheads) and a transmigrated PMN (arrow). Transmigrating PMNs are characterized by both clearly visible cell bodies and extended protrusions; the latter are visible under phase-contrast optics (A), but not under scanning electron microscopy (B,C). A transmigrated PMN is almost invisible from the top but appeared as a slightly raised area (B,D).