IL6 and major depressive disorder: In depression, for instance, there is evidence of low-grade systemic inflammation as indexed by elevated concentrations of C-reactive protein (CRP >3 mg/L) in 21–34% of patients [3], along with increased concentrations of interleukin-6 (IL-6) and other inflammatory cytokines in blood and in cerebrospinal fluid (CSF) [[4], [5], [6], [7], [8]].