H. parasuis LppA reduces porcine endothelial cell integrity. (a, b) PAECs were co-cultured with wild-type PAMs, and PAMs were infected by wild-type SH0165, δlppa mutant, or C-lppA strains (100 MOI) for 2 h. Protein expression levels of phospho-LKB1 (T189), LKB1, phospho-AMPK (S458), AMPK, phospho-mTOR (S2448), and mTOR in PAECs (a), as well as the claudin-5 and occludin (b), were determined using western blot analysis. The antibodies were diluted as described above. β-actin served as a loading control, and the relative protein level was calculated with ImageJ software and normalized to β-actin. **p<0.01 compared with the untreated group, ##p<0.01 compared with the wild type H. parasuis-infected group. (c) TEER of PAECs was measured at 0, 6, 12, 24, 48, and 2 h after infecting PAMs by wild-type SH0165, δlppa mutant, or C-lppA strains (100 MOI). TEER levels were displayed as a percentage of the TEER before treatment. **p<0.01 compared with the wild-type SH0165 group. (d) claudin-5 and occludin expression in primary PAECs was analysed using qRT-PCR. **p<0.01 compared with the wild-type SH0165 group. Error bars represent the mean ± SEM (n = 3).