TABLE 4.
Effect of tryptophan on cytokine inhibition of T. gondii growth
| Treatment | Inhibition of T. gondii growth (% of control)a
|
|||
|---|---|---|---|---|
| Control astrocytes
|
iNOS−/− astrocytes
|
|||
| Medium | Cytokines + tryptophan | Medium | Cytokines + tryptophan | |
| IFN-γ | 35.5 ± 2.3 | 38.7 ± 3.4 | 32.3 ± 2.3 | 31.0 ± 2.1 |
| IFN-γ, IL-1 | 28.4 ± 3.9 | 33.3 ± 3.5 | 21.1 ± 1.1 | 15.6 ± 2.0 |
| IFN-γ, IL-6 | 21.5 ± 2.9 | 29.6 ± 1.4 | 20.5 ± 1.7 | 17.0 ± 4.1 |
| IFN-γ, IL-1, IL-6 | 20.6 ± 2.1 | 22.8 ± 5.4 | 25.5 ± 4.9 | 19.5 ± 1.7 |
| IFN-γ, TNF-α | 23.5 ± 3.5 | 22.5 ± 5.1 | 23.4 ± 0.7 | 16.8 ± 5.6 |
| IFN-γ, TNF-α, IL-6 | 21.0 ± 2.2 | 23.7 ± 1.1 | 15.0 ± 3.8 | 12.5 ± 1.6 |
a
Mean ± SD of two separate experiments for astrocyte cultures treated with IFN-γ (100 U/ml), IL-1 (1 ng/ml), IL-6 (100 U/ml), and TNF-α (100 U/ml) in the presence and absence of tryptophan (100 μg/ml) and for control cultures incubated with medium alone. Cells were incubated with cytokines for 72 h prior to infection, and tryptophan was added at the time of cytokine addition; [3H]uracil (2.5 μCi/ml) was added 2 h after infection, and cells were harvested 48 h later. No statistically significant difference was detected between any of the cultures as determined by Student’s t test and analysis of variance.