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

Scientific RepoRts | 6:26748 | DOI: 10.1038/srep26748 Different sensitivity of PTEC and PBEC to the cytotoxic effect induced by suilysin of S. suis. Cytotoxicity was examined by determining the release of cellular lactate dehydrogenase (LDH), a widely used marker for cellular damage. PTEC and PBEC were infected with S. suis wt, either of the mutants (10Δ sly and 10Δ cpsΔ sly), or either of the complemented mutant strains cW461F and cS148, respectively, and analyzed for cytotoxic effects in comparison to mock-infected cells. As shown in Fig. 2A , cytotoxicity induced by the wt strain increased in a time-dependent manner from 4 hpi to 72 hpi. LDH release induced by the wt strain at 4 hpi in PBEC (4-fold increase) was similar to that in PTEC (3-fold), but at 48 hpi it was significantly higher in PBEC (7.3 fold) than in PTEC (2.3 fold). To elucidate whether cytotoxic effects would also influence integrity of the cellular barrier, we determined the TEER of PTEC and PBEC, which is indicative of the formation of tight junctions and an intact epithelial barrier 23 . Results revealed that mock-infected PTEC and PBEC remained unaffected until end of the experiment (96 hpi). In comparison, TEER of PTEC and PBEC infected with the wt strain showed a significant decrease starting at 72 hpi and 48 hpi, respectively, whereas that of PTEC/PBEC infected by either of the two suilysin-deficient mutants was similar to the control ( Figure S2 ).