The fact that not only sTNF but also sTNF-RI, sTNF-RII, and sCD163 were decreased in SpA versus RA SF indicates that impaired ADAM17 (or TACE) expression and/or activity might be implicated in the relative overexpression of tmTNF over sTNF in the SpA synovial lining layer. This evidence concerns the gene CD163 and rheumatoid arthritis.