Role of interleukin 17 (IL-17) in the inflammatory hypothesis of depression

•Many studies indicate elevated blood levels of interleukin 17 in depressed patients.•Interleukin 17 plays an important role in autoimmune diseases.•There are several pathomechanisms by which interleukin 17 and Th17 cells may be linked with the development of depression. Depression is one of the most common mental disorders. Despite its high prevalence, the etiopathogenesis of depression is not yet fully understood. Only around 1/3 of depressed patients remit in response to standard antidepressant treatment. Hence further studies are needed to search for potential pathomechanisms leading to depression and thereby identify novel biological targets for antidepressant therapies. The aim of this review paper is to explain the potential role of interleukin-17 in the pathogenesis of depression in the context of the inflammation hypothesis of this disorder. In this paper, we present a literature review of interleukin 17 (IL-17) blood levels in patients with depressive disorders and discuss potential pathomechanisms linking this cytokine to the development of depression.