IL17A and spondyloarthropathy: Indeed, going back to rheumatic diseases in the synovial membrane where TH17 response is considered pivotal, the neutrophils [237] and the mast cells are indeed the principal source of IL-17 for the case of rheumatoid arthritis [238, 239] and mast cells are also relevant IL-17 secretors in the spondyloarthritis [240], and keratinocyte derived IL-17C is the predominant isoform in psoriatic skin lesions [171].