Taken together, these results demonstrate that MPs derived either from synovial fluids from RA and OA patients or from leukocytes are able to induce BAFF, TSLP, and SLPI release by activated RA FLSs and could participate in cell-cell interactions leading to the proinflammatory response of FLSs as well as in their implication in the B-cell autoimmune response. Here, SLPI is linked to rheumatoid arthritis.