IL-17A

Interleukin-17A (IL-17A), also known as CTLA-8, belongs to the IL-17 cytokine family. IL-17A is expressed in memory Th17 cells and is a product of memory CD4⁺ T cells^[1]. In addition to Th17 cells, IL-17A is also produced by a wide variety of immune cells, including CD8⁺ T cells, γδT cells, natural killer T (NKT) cells, monocytes, and neutrophils^[2][3]. IL-17A plays a critical role in host defense mechanisms against many bacterial and fungal pathogens as well as allergic and autoimmune responses^[1][2]. IL-17A induces the production of antimicrobial peptides (defensins and S100 proteins), cytokines (IL-6, G-CSF, and GM-CSF), chemokines (CXCL1, CXCL5, IL-8, CCL2, and CCL7), and matrix metalloproteinases (MMP1, MMP3, and MMP13)^[2]. IL-17A is detrimental in viral infection through promoting neutrophilic inflammation^[1]. IL-17A is a homodimeric cytokine and shares similar biological activities with IL-17F. IL-17A binds to IL-17RA with high affinity, and IL-17RA is required for the biological activity of IL-17A. IL-17A cannot bind to T cells, B cells, and myeloid cells that are deficient in IL-17RA. IL-17A has been implicated in a variety of autoimmune diseases, such as rheumatoid arthritis, multiple sclerosis, inflammatory bowel disease, asthma, and psoriasis^[4]. IL-17A also plays a pathogenic role in cancer. In tumorigenesis, IL-17A recruits myeloid derived suppressor cells (MDSCs) to dampen anti-tumor immunity. IL-17A also enhances tumor growth in vivo through the induction of IL-6^[1]. Murine IL-17A is a 21 kDa glycoprotein with 147 amino acids and 63% amino acid homology with human IL-17A (155 amino acids)^[2].