TSPO and major depressive disorder: This is consistent with previous studies which have demonstrated a downregulation in TSPO expression from baseline in several neurological and psychiatric disorders, including PTSD (Gavish et al., 1996), depression (Chelli et al., 2008; Sarubin et al., 2016), and reduced TSPO ligand binding in PET imaging of recent onset schizophrenia (Notter et al., 2018a), despite the induction of systemic cytokine immune responses.