Efficient suilysin-mediated invasion and apoptosis in porcine respiratory epithelial cells after streptococcal infection under air-liquid interface conditions

Meng, Fandan; Wu, Nai-Huei; Seitz, Maren; Herrler, Georg; Valentin-Weigand, Peter

Apart from its role in adherence and invasion, suilysin is also responsible for the cytotoxicity of S. suis. CDC are important components of pathogenic streptococci. The soluble monomeric forms assemble to ring-shaped oligomeric structures on the surface of the cell 47 . Upon insertion of the oligomers into the plasma membrane, the resulting pore formation perforates the membrane and exerts a cytotoxic effect. In the case of suilysin, cytotoxicity has been demonstrated with different types of immortalized cells [30] [31] [32] [33] . Our results demonstrate a To quantify the apoptotic cells on PBEC, the areas containing red-fluorescent cells were determined from panels A and B. Results are expressed as x-fold increase compared to mock-infected cells (mock). Results are expressed as means ± SEM and significance, indicated by * * * (P < 0.0001), was determined using one-way-ANOVA and Tukey multiple comparison test. Experiments were performed at least three times. pronounced cytotoxic effect also for well-differentiated airway epithelial cells. Notably, this effect was absent in a strain expressing a derivative of suilysin which carries a point-mutation (W461F) of the domain responsible for macropore-formation. In fact, immunostaining revealed large amounts of cell surface-located suilysin molecules, at least some of which might represent formation oligomeric pore complexes. The large amount of suilysin may again be explained by the ALI culture conditions that enable high local concentrations of the toxin. The strong cytotoxic effect of suilysin also explains the lesions that were observed at 24 hpi in the aiway epithelial cell layer that expanded until the whole epithelium was damaged. Future studies have to analyze why the cellular damage appeared to be more pronounced in bronchial cells than in tracheal cells.