What is Interleukin-17 (IL-17)
Interleukin 17 (IL-17 or IL-17A) is produced by T helper 17 (Th17) cells, macrophages, dendritic cells (DC) and natural killer to against infections such as AIDS, malaria, and tuberculosis. The T cells, macrophages, dendritic cells (DC) and natural killer are kinds of immune system white blood cells, they locate and ‘eat’ harmful particles such as bacteria, viruses, fungi, and parasites. [1,2]
Depleted IL-17 cause extracellular bacterial and fungi infections.
Elevated IL-17 level is linked with immune-mediated diseases, rheumatoid arthritis, systemic lupus erythematosus, psoriasis, inflammatory bowel disease. [1,4,5]
Three IL-17 inhibitors have been approved for the treatment of psoriasis: ixekizumab and secukinumab, which target IL-17A, and brodalumab, which blocks the IL-17 receptor A. 
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- IL17A interleukin 17A [ Homo sapiens (human) ] Gene ID 3605 https://www.ncbi.nlm.nih.gov/gene/3605
- INTERLEUKIN 17A; IL17A https://omim.org/entry/603149
- Jean L. Bolognia , Julie V. Schaffer , Lorenzo Cerroni, edit. Dermatology, Fourth edition, China: Elsevier, 2018, ISBN 978–0‐7020–6275–9. page2251-2253