NOS2 and major depressive disorder: In patients with depression, pathogen-associated molecular patterns (PAMPs) such as inducible nitric oxide synthase (iNOS) and nitric oxide (NO), and danger-associated molecular patterns (DAMPs) such as IL-1β and interleukin-18 (IL-18) enter the cytoplasm of hippocampal microglia (Tian et al., 2024).