IL6 and major depressive disorder: Hence, high concentrations of TNF-α and IL-6 might be important factors for promoting the development of cognition impairment, thereby increased cognition impairment occurrence; and 2) a high level of common pro-inflammatory cytokines (including TNF-α, IL-1β, and IL-17) might affect indoleamine 2,3-deoxygenation enzyme-1 (IDO1), subsequently influence 5-hydroxytryptamine (5-HT) (an important neurotransmitter related to depression), and eventually increase anxiety and depression occurrence in AIS patients (19-, , 22).