TSPO and major depressive disorder: Currently, in addition to peripheral biomarkers of inflammation such as CRP, interleukin (IL)-6, IL-1 beta, and tumor necrosis factor (TNF)-alpha, we are able to assess microglia activation in MDD as a neuro-inflammatory biomarker using translocator protein (TSPO) density in positron emission tomography (PET) scans (51).