TNF-α WT and KO astrocytes were seeded in 96-well plates at 1 × 105 cells per well and incubated overnight. The following day, cells were treated with the indicated concentrations of IL-1β for 24 h, whereupon nitrite levels were determined. Significant differences between unstimulated and IL-1β-treated WT astrocytes are denoted with asterisks (**, p < 0.001), whereas alterations between TNF-α WT versus KO astrocytes are indicated by hatched signs (##, p < 0.001). Results are representative of two independent experiments.