Figure 1

Invasion of Nm into HIBCPP cells. Invasion assays were performed in the inverted cell culture insert system. Invasion of the different Nm strains was analyzed by double immunofluorescence. (A) Schematic representation of the inverted cell culture insert system. Cells are grown on the lower side of the filter supports. Microvilli are indicated at the apical side. (B) HIBCPP cells were infected for 4 h at a multiplicity of infection of 10 and subsequently subjected to double immunofluorescence staining to distinguish intracellular and extracellular bacteria. Basolateral invasion was observed for Nm MC58 and the acapsular mutant strain MC58siaD^-. Invasion was significantly attenuated by the presence of a capsule. Only marginal invasion was detected after infection with the carrier isolate α14. ** (highly significant; P <0.01), *** (extremely significant; P <0.001); when MC58 or MC58siaD^-, respectively, were compared to α14. ### (extremely significant; P <0.001); when MC58siaD^- was compared to MC58.