STAT3 and schizophrenia: First, brain-derived neurotrophic factor (BDNF) is adversely related to IL-23 and illness severity ratings in schizophrenia [79], and a first protein-protein interaction (PPI) network created using FEP/FES genes shows that BDNF is part of the same immune PPI network as STAT3, IL-6, TNF-α, IL-1β, and IL-10 [80].