In patients affected by major depressive disorder, signs of microglial activation such as increased translocator protein (TSPO) volume, a positron emission tomography (PET) scan marker of microglial activation (previously referred to as peripheral benzodiazepine receptors (PBR)), have been reported in comparison with healthy controls (Setiawan et al., 2015). This evidence concerns the gene TSPO and major depressive disorder.