IL17A and rheumatoid arthritis: To determine whether synovial Tc17 cells are enriched only in PsA or are also enriched in other SpA types, we stimulated paired PBMCs and SFMCs from patients with PsA, patients with other types of SpA, and patients with rheumatoid arthritis (RA) ex vivo with PMA/ionomycin and assessed the frequency of IL‐17A+CD8+ T cells by flow cytometry (Figures 1A and B).