IL6 and major depressive disorder: Interestingly, we found that serum IL-6 levels were higher in patients during depressive episodes of BD (4.379 ± 0.3587 vs 2.141 ± 0.3164, P <.01; Fig. 3A), but not MDD (3.105 ± 0.5200 vs 2.141 ± 0.3164, P >.05; Fig. 3A), than in healthy controls.