IL6 and major depressive disorder: Thus, in major depressive disorder (MDD) and bipolar disorder (BD), the number of prior depressive and manic episodes, as well as SBs, are associated with an increase in plasma IL-1β, sIL-1RA, IL-6, TNF-α, and neopterin, lowered antioxidant enzyme activities, and damage to lipids and proteins [20,21,22,23], while other findings indicate that immune-inflammatory responses are more pronounced in later stages of illness [24,25].