Interleukin-17 (IL-17) is a key cytokine in the mammalian immune system, involved in both host defense and autoimmune diseases. It is produced by various innate immune cells, including T cells, macrophages, and dendritic cells. IL-17 plays a central role in inflammation and autoimmunity, inducing the expression of genes that promote inflammatory responses, such as cytokines, chemokines, and antimicrobial peptides. These include IL-6, granulocyte-colony-stimulating factor, tumor necrosis factor-α, CXCL1, CXCL2, CCL20, and defensins. IL-17 also contributes to the pathogenesis of autoimmune diseases like rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), and inflammatory bowel disease (IBD), as well as chronic infections. In RA, IL-17 promotes inflammation and bone destruction by inducing pro-inflammatory cytokines and matrix metalloproteinases, leading to cartilage and bone erosion. It also enhances the recruitment of immune cells to the synovium, exacerbating joint damage. In SLE, IL-17 contributes to autoantibody production and the formation of ectopic germinal centers, which are associated with disease progression. In IBD, IL-17 is involved in the Th17 pathway, which is linked to chronic inflammation and tissue damage. IL-17 also plays a protective role in infections, particularly in mucosal sites like the lungs, gut, and oral cavity, by inducing antimicrobial peptides and chemokines that recruit immune cells to fight pathogens. The IL-17 signaling pathway involves the IL-17RA and IL-17RC receptors, which activate downstream signaling pathways such as NF-κB and C/EBP, leading to the expression of target genes. IL-17 synergizes with other cytokines like IL-23, IL-22, and TNF-α to enhance inflammatory responses. However, in some cases, IL-17 can be detrimental, contributing to immunopathology. The balance between IL-17's protective and harmful effects is crucial in determining disease outcomes. Targeting IL-17 or its signaling pathways is a promising approach for treating autoimmune and inflammatory diseases.Interleukin-17 (IL-17) is a key cytokine in the mammalian immune system, involved in both host defense and autoimmune diseases. It is produced by various innate immune cells, including T cells, macrophages, and dendritic cells. IL-17 plays a central role in inflammation and autoimmunity, inducing the expression of genes that promote inflammatory responses, such as cytokines, chemokines, and antimicrobial peptides. These include IL-6, granulocyte-colony-stimulating factor, tumor necrosis factor-α, CXCL1, CXCL2, CCL20, and defensins. IL-17 also contributes to the pathogenesis of autoimmune diseases like rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), and inflammatory bowel disease (IBD), as well as chronic infections. In RA, IL-17 promotes inflammation and bone destruction by inducing pro-inflammatory cytokines and matrix metalloproteinases, leading to cartilage and bone erosion. It also enhances the recruitment of immune cells to the synovium, exacerbating joint damage. In SLE, IL-17 contributes to autoantibody production and the formation of ectopic germinal centers, which are associated with disease progression. In IBD, IL-17 is involved in the Th17 pathway, which is linked to chronic inflammation and tissue damage. IL-17 also plays a protective role in infections, particularly in mucosal sites like the lungs, gut, and oral cavity, by inducing antimicrobial peptides and chemokines that recruit immune cells to fight pathogens. The IL-17 signaling pathway involves the IL-17RA and IL-17RC receptors, which activate downstream signaling pathways such as NF-κB and C/EBP, leading to the expression of target genes. IL-17 synergizes with other cytokines like IL-23, IL-22, and TNF-α to enhance inflammatory responses. However, in some cases, IL-17 can be detrimental, contributing to immunopathology. The balance between IL-17's protective and harmful effects is crucial in determining disease outcomes. Targeting IL-17 or its signaling pathways is a promising approach for treating autoimmune and inflammatory diseases.