TNF and major depressive disorder: Crucially, a quantitative analysis showed that there was a difference in TNF-α concentrations regarding the source of the sample, reaching a significant difference in serum in the first episode of depression (SMD = 1.19 [0.77, 1.61], p < 0.00001; n = 2) and plasma in drug-naïve patients (SMD = 0.47 [0.26, 0.68], p < 0.0001; n = 3).