IL6 and depressive symptom measurement: Patients suffering from depression exhibit increased levels of the proinflammatory cytokine interleukin-6 (IL-6) while at rest and exhibit greater social stress-induced IL-6 levels, which are normalized following antidepressant therapy (Frommberger et al., 1997; Pace et al., 2006; Fagundes et al., 2013).