IL-17F

Interleukin-17F (IL-17F) belongs to the IL-17 cytokine family. IL-17F is expressed in activated CD4 T cells, activated monocytes, basophils and mast cells. IL-17F can be produced by differentiated TH17 cells, lamina propria T cells, memory CD4⁺ T cells, γδ T cells and NKT cells^[1]. IL-17F is an inflammatory cytokine that induces many proinflammatory cytokines and chemokines. IL-17F induces TGF-β and IL-2 in vein endothelial cells, induces ICAM1 and GM-CSF expression in airway bronchial epithelial cells, and also induces CCL2, CCL7, TSLP and MMP13 in lung fibroblast cells. IL-17F upregulates the expression of IL-6 and CXCL1 in fibroblasts and epithelial cells. IL-17F induces antimicrobial peptides including hBD-2, S100A7, S100A8 and S100A9 with IL-22. IL-17F can synergize with IL-23 in human eosinophils to promote the production of IL-1β and IL-6^[1]. IL-17F is a homodimeric cytokine. IL-17F shares the most similarities with IL-17A (50% homology) and can be produced as an IL-17AF heterodimer. IL-17A, IL-17F and IL-17A/F use the same receptor complex: IL-17RA and IL-17RC heterodimer. And they trigger qualitatively similar signaling pathways, IL-17F exhibits the lowest biological activity among IL-17 and IL-17A/F heterodimer^[1][2]. IL-17F shows about 100–1000 times lower affinity to the IL-17RA subunit than IL-17A, and does not compete with IL-17A binding to IL-17RA^[1][3]. IL-17F plays a protective role in colon cancer development^[4]. Human and mouse IL-17F share only 55.90% sequence identity.