We documented significantly higher levels of interferon-gamma (IFN-γ) in medically healthy adolescents with major depressive disorder compared to healthy controls (230, 231); unexpectedly, however, we found that suicidal depressed adolescents had decreased levels of tumor necrosis factor-alpha (TNF-α) compared to non-suicidal adolescents with depression (231). Here, TNF is linked to major depressive disorder.