image: This graphic shows the proposed pathway for GPVI-dependent participation of platelets in arthritis via microparticles. GPVI-expressing platelets activated by collagen produce copious amounts of IL-1-rich microparticles (MPs) (left panel and inset). The precise anatomic location of platelet activation, and the route by which microparticles enter the joint (dashed red line with arrows), remain unknown. Platelet MPs (~0.2 -1 μm in diameter), detectable at high levels in inflammatory synovial fluid, interact with tissue cells including fibroblast-like synoviocytes (FLS) and synovial fluid leukocytes (right panel). This interaction elicits further inflammatory effector functions from target cells thereby amplifying synovitis. In the case of FLS, platelet MPs promote elaboration of IL-8 and other mediators that are capable of leukocyte chemoattraction to the joint (right panel). Platelet microparticles attached to neutrophils, as found in diseased synovial fluid, may also stimulate neutrophil effector functions, although this remains to be established (question mark right panel). This image relates to an article that appeared in the Jan. 29 2010, issue of Science, published by AAAS. The study, by Dr. Eric Boilard at Brigham and Women's Hospital in Boston, Mass., and colleagues, was titled, "Platelets Amplify Inflammation in Arthritis via Collagen-Dependent Microparticle Production." view more
Credit: Illustration courtesy of Steve Moskowitz, Advanced Medical Graphics