IDO1 and schizophrenia: We had three major findings: (1) The elevated levels of IDO and inflammatory cytokines including IL-1β, IL-6, TNF-α, IL-17, IL-4, and IFN-γ can be observed in the early stages of schizophrenia; (2) IDO levels were significantly positively correlated with TNF-α and IFN-γ levels; (3) IDO levels were significantly positively correlated with negative symptoms of schizophrenia.