CXCL8 and depressive disorder: Tools: PCI-total (cognition), UCLA Loneliness Scale (loneliness), Perceived Stress Scale (stress), PROMIS (fatigue, anxiety, depression), PSQI (sleep quality), and Epworth Sleepiness Scale (daytime sleepiness); Biomarkers: 13 cytokines (TNF-α, GM-CSF, INF-γ, IL-2, IL-1b, IL-5, IL-7, IL-8, IL-10, IL-13, IL-6, IL-2, and IL-4)