Inflammation that is mediated by microglia activation plays an important role in the
pathogenesis of depression. Microglia activation can lead to an increase in the levels of
proinflammatory cytokines, including TNF-α, which leads to neuronal apoptosis in the specific
neural circuits of some brain regions, abnormal cognition, and treatment-resistant depression
(TRD). Protein kinase C (PKC) is a key regulator of the microglia activation process. The
investigators assume that the abnormality in PKC might be the serum biomarkers of depression.