TNF and tricho-dento-osseous syndrome: Secretion of cytokines and proinflammatory factors as γ-interferon (γ-INF) and tumor necrosis factor-α (TNF-α) induces IDO gene expression, whereas antidepressant drugs, tricyclic or selective 5-HT reuptake inhibitors (SSRIs), are able to inhibit TDO, while increasing Trp plasma levels and 5-HT synthesis [41, 57, 58].