However, there is some singularities in PsA that merit more in-depth research: the role of IL-17-positive mast cells in PsA inflammation and in IL-17 A regulation; the role of ectopic lymphoid neogenesis in PsA, and to know if there is distinct functional subsets of synovial FLS in PsA as in RA. Here, IL17A is linked to rheumatoid arthritis.