The principal findings of this study were as follows: (i) scores of depression scales were decreased after anti-TNF-α infusion and this effect was to a degree, but not entirely, reducible to disease activity; (ii) there was no change in the TRP/CAA ratio after anti-TNF-α infusion and neither scores of depression scales, nor immune parameters were associated with TRP/CAA ratio; (iii) immune activation was higher in patients with current/past depressive disorder. The gene discussed is TNF; the disease is major depressive disorder.