TNF and major depressive disorder: Twenty samples from normal and MDD patients with various HHV-6 (positive or negative)/TNF-α promoter statuses (healthy: positive/G n = 3, positive/G/A n = 5, negative/G/A n = 5, and negative/G n = 5; MDD patients being treated with drugs: positive/G n = 1 and negative/G n = 1) were available for the ELISA.