IL6 and depressive disorder: One of the key neuroimmune factors is interleukin (IL)-6, which is upregulated in central nervous system disorders (Gadient and Otten, 1997) and has been implicated in conditions, such as schizophrenia, autism, depression, Parkinson’s disease, and Alzheimer’s disease (Garay and McAllister, 2010; Felger and Lotrich, 2013; Wei et al., 2013; Borsche et al., 2020).