IL17A and psoriatic arthritis: We first tested four JAK inhibitors of different reported specificity (see Supplementary Table S1) for their ability to inhibit secretion of IL-17A from purified blood CD4+ T cells cultured for 3 days in an initial cohort of 43 Ankylosing Spondylitis (AS), 16 Psoriatic Arthritis (PSA), 18 Rheumatoid Arthritis (RA) patients and 26 healthy controls (HC).