We recently proposed that mast cells may contribute to SpA synovitis by indicating that the number of infiltrating mast cells was specifically increased in SpA versus RA synovitis, SpA synovial mast cells contained IL-17A as assessed by immunostaining, and ex vivo targeting of mast cells with imatinib reduced inflammation in synovial biopsy cultures [13]. This evidence concerns the gene IL17A and rheumatoid arthritis.