Electron microscopic view of a PMN travelling through the CP monolayer. (A, G, H) PCPECs were stimulated with S. suis strain 10, (B, I, J) S. suis strain 10 Δcps or (C-F) TNFα. (A) A PMN is closely associated to two epithelial cells (CP), near the tight junction (thin arrow). MV = microvilli. (B) In this case, the PMN has nearly touched the apical membrane for release of the cell into the upper compartment. The tight junction is labelled by an arrow. The space between the PMN and the epithelial cell (CP) is labelled by small asterisks. (C) Inability of PMN to open the tight junction, but in parallel, the PMN tries to enter the epithelial cell in order to reach the surface of the epithelial cell which is strongly enlarged by numerous microvilli (MV). In addition, the lower magnification in C suggests an indentation of the apical surface of the epithelial cell layer forming funnel-like structures (asterisks in C). (D) The area shown in D at higher magnification is labelled in C by a thick arrow. (E) A similar funnel is cross-sectioned in a flat section parallel to the filter (asterisks). (F) Higher magnified area labelled by a thick arrow in (E). The section runs parallel or slightly oblique to the apical surface of the monolayer. The PMN is completely surrounded by vesicular membranes which, in the REM investigation (Figure 5E), can be identified as formed by the PMN itself. Again, the tight junction (thin arrow) remains closed and unaffected. (G) PMN harbouring encapsulated S. suis strain 10 in vacuoles. (H) Enlargement of the marked section of G; bacteria are marked with a asterisks. (I) PMN harbouring non-encapsulated S. suis strain 10 Δcps in vacuoles (white marks). (J) Enlargement of the marked section of I; bacteria are marked with an asterisk. Scale bar, as indicated.