IL-17 producing T cells in human chronic inflammatory disease A major interest of the lab is IL-17 biology. The IL-17 family consist of IL-17A, B, C, D, E and F. IL-17A is a potent pro-inflammatory cytokine which promotes angiogenesis, osteoclastogenesis and inflammatory cytokine and chemokine production. IL-17A-producing T cells are therefore thought to play a pivotal role in the immunopathology of inflammatory arthritis. Using multiparameter flow cytometry, RNA sequencing, Luminex, cellular and functional assays, we have studied the presence, function and regulation of IL-17A producing CD4+ (Th17) and CD8+ (Tc17) T cells in the context of rheumatoid and psoriatic arthritis. Through these efforts, we have identified that activated monocytes play an important role in promoting human Th17 cell induction. We have also discovered that whilst Th17 cells are enriched in the synovial fluid in both RA and PsA, Tc17 cells are only enriched in the inflamed PsA joint. These Tc17 cells have a pro-inflammatory profile and a tissue-resident memory phenotype. Ongoing work is aimed at determining the pro-inflammatory function of Tc17 cells and how these cells are regulated. We are also interested in understanding the function of the other IL-17 family members in the context of arthritis.