CRP and major depressive disorder: For example, psychological stress has generally been shown to increase levels of C-reactive protein (CRP), interleukin (IL)-6, IL-1β, and tumour necrosis factor (TNF)-α in otherwise healthy individuals (Steptoe et al., 2007), whereas for obese individuals, elevated levels of IL-5, IL-12, and interferon-ɣ (IFN-ɣ) have been associated with depression (Schmidt et al., 2014).