IL6 and major depressive disorder: Involvement of inflammation in negative mood and poor cognitive function is supported by numerous reviews that repeatedly showed an increased incidence of negative mood symptoms with elevated levels of pro-inflammatory markers (CRP, TNF-α, IL-1β, IL-2, and IL6) in peripheral blood and cerebrospinal fluid (CSF) in patients with MDD (Dowlati et al., 2010; Hannestad et al., 2011; Hiles et al., 2012).