Table 2.

Evidence for and against the role of IL-6 in depression.

Evidence for

1. Preclinical studies suggest that increased IL-6 levels whether by stress, lipopolysaccharide or direct IL-6 injection produced depressive-like behaviors in rodents. 2. Il6 knockout mice showed less despair behaviors to stress. 3. Most published findings on serum/plasma IL-6 have demonstrated a correlation between high levels of this interleukin and MDD. 4. Longitudinal study demonstrated that higher serum IL-6 levels would increase future risks for depression. 5. IL-6 antibodies made significantly greater improvements on depressive symptoms in patients with autoimmune diseases.

Evidence against

1. Results of IL6 genetic association studies in MDD have been inconsistent. 2. Different types of antidepressant medication may have divergent effects on IL-6 levels. 3. Intracerebroventricular anti-IL-6R antibody injection in susceptible mice induced no antidepressant effects.