Scanning electron microscopical analysis and serial sections of PMNs transmigrating through PCPEC monolayers. Arrows mark cell borders. (A-C) The cell in A and the lower cell in B could have been overcome the barrier in the middle of an epithelial cell, apart from the cell border, whereas the smaller cell in B, and also the cell in C, could have just transmigrated between two epithelial cells. (D) A PMN lies in an indentation in the middle of an epithelial cell, corresponding to the funnel-like structure as described in Figures 4 and 5. (E) The vesicular structures (star) of a transmigrating PMN are shown which correspond to the surface foldings of the PMN in ultrathin sections (asterisk. Scale bar, as indicated.in Figure 4F). (F) The image shows a preparation artifact allowing a look into the space below the surface of the epithelial monolayer, where a PMN is waiting to transmigrate (arrow points to the expected direction of the cell). Here it is evident that the PMN will transmigrate transcellularly, because no cellular border can be observed.