For instance, Al-Hakeim et al. (2015) found elevated serum levels of IL-6, IL-18, TNF-α, and sIL-2R in MDD patients compared to controls, while Draganov et al. (2019) suggested that polymorphisms in the IL1-β and IL6R genes might influence treatment response in severe depressive disorder. This evidence concerns the gene IL6 and depressive disorder.