Impact of IL-17 on Cells of the Monocyte Lineage in Health and Disease

Discovered in 1993, IL-17 has been the focus of intensive research during the last decade, in particular because of its neutrophil-accumulating capacity in several mammalian organs. We now know that the IL-17 family includes as a minimum 6 members, of whom at least IL-17A and IL-17F can be produced by T cells. Thus, IL-17 is positioned at the interface of acquired and innate immunity and constitutes a link between T cell activity and the accumulation of neutrophils locally in organs. Interestingly, there is now accumulating evidence that IL-17 has effects on myeloid cells other than neutrophils as well, namely on cells of the monocyte lineage. This review article scrutinizes the evidence that IL-17 exerts a functional impact on the cytokine production and functional activity in cells of the monocyte lineage in health and disease. Notably, this evidence includes data suggesting that there are conditions in which cells of the monocyte lineage are likely to play a significant pathogenic role and where IL-17 is directly controlling the activity of these key effector cells.