IL-1β induces activation of pro-apoptotic inos/NO axis in A. hydrophila-infected HKM. HKM transfected with sc-siRNA, il1b-siRNA, inos-siRNA or pre-incubated with L-NIL, Z-DEVD-FMK and infected with A. hydrophila and at 24 h p.i., (a) HKM apoptosis, (b) the expression of inos mRNA was studied, (c) nitrite levels were measured, and (d) caspase-3 activity was studied at 24 h p.i. Vertical bars represent mean ± SE (n = 3). Asterisk indicates significant difference between indicated groups (*p < 0.05). HKM, uninfected HKM; HKM+B, HKM infected with A. hydrophila; HKM+L-NIL+B; HKM pre-incubated with L-NIL and infected with A. hydrophila; HKM+Z-DEVD-FMK+B, HKM pre-incubated with Z-DEVD-FMK and infected with A. hydrophila; HKM+sc-siRNA, HKM transfected with sc-siRNA; HKM+sc-siRNA+B, HKM transfected with sc-siRNA infected with A. hydrophila; HKM+il1b-siRNA+B, HKM transfected with il1b-siRNA infected with A. hydrophila; HKM+inos-siRNA+B, HKM transfected with inos-siRNA infected with A. hydrophila.