IL6 and major depressive disorder: To understand the effect of CRP, cytokines, and cortisol in the pathogenesis of anhedonia in MDD, this study first analyzed and compared serum cortisol, CRP, and cytokines, including TNF-α, interferon-γ (IFN-γ), IL-2, IL-4, IL-6, IL-10, and IL-17A between patients with MDD and healthy controls (HCs).