![]() Platelets form MPs and participate in arthritis pathophysiology via stimulation of the collagen receptor GPVI. ( E) Flow cytometric quantification of MPs in RA SF derived from the indicated cell types ( n = 19 donors). ( D) Flow cytometric quantification of platelet (CD41 +) MPs in SF from juvenile idiopathic arthritis (JIA, n = 6), psoriatic arthritis (PA, n = 19), and gout ( n = 14). ( C) Flow cytometric quantification of CD41 + platelet MPs (<1 μm as determined by size calibration beads) in RA and OA SF after removal of leukocytes by centrifugation ( n = 20 donors per group). (Gray fill, isotype control.) Data are representative of profiles from eight RA patients. Events were gated based on the forward-scatter parameters indicated in (A). ( B) Representative histogram of CD41 + (black fill) platelet MPs resident in RA SF. Populations identified by further gating and lineage marker staining are labeled. ( A) Forward- by side-scatter profiles of events in RA SF. Cells in freshly isolated RA SF were stained with lineage markers: CD15 (neutrophils), CD3 (T cells), CD14 (monocytes and macrophages) and CD41 (platelets), or the appropriate isotype controls and analyzed by flow cytometry. Platelet MPs are abundant in inflammatory SF. Thus, these findings demonstrate a previously unappreciated role for platelets and their activation-induced microparticles in inflammatory joint diseases. Using both pharmacologic and genetic approaches, we identified the collagen receptor glycoprotein VI as a key trigger for platelet microparticle generation in arthritis pathophysiology. Consistent with these findings, depletion of platelets attenuated murine inflammatory arthritis. Platelet microparticles were proinflammatory, eliciting cytokine responses from synovial fibroblasts via interleukin-1. ![]() ![]() We identified platelet microparticles-submicrometer vesicles elaborated by activated platelets-in joint fluid from patients with rheumatoid arthritis and other forms of inflammatory arthritis, but not in joint fluid from patients with osteoarthritis. We investigated the role of platelets in the autoimmune disease rheumatoid arthritis. In addition to their pivotal role in thrombosis and wound repair, platelets participate in inflammatory responses. ![]()
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