FIG. 3.

Pathogenic and asymptomatic carrier isolates of H. somnus induce bovine endothelial cell apoptosis, as detected by Hoechst 33342 staining and TUNEL. Volumes containing 5 × 10⁴ endothelial cells were adhered to glass coverslips and incubated with pathogenic H. somnus isolates 8025, 649, and 2336 and asymptomatic carrier isolates 127P and 129Pt at an MOI of 10:1 for 6 h at 37°C with 5% CO₂. Apoptosis was detected by Hoechst 33342 staining and TUNEL on separate coverslips. Controls consisted of untreated cells (UT) and 200 nM staurosporine (Stauro)-treated endothelial cells. These data represent the mean ± SEM of three independent experiments. All isolates of H. somnus used in this experiment induced significant levels of endothelial cell apoptosis compared to those of untreated endothelial cells (P < 0.05; Tukey-Kramer significant difference test).