Proposed pathway for the formation of gaps and amplification of the vasculature permeability by platelets during arthritis. (Top panel) Gaps between endothelial cells in arthritic joints are formed. The GPVI-expressing platelets are activated by the leakage during disease. Note that the precise anatomic location of platelet activation, and the route by which microparticles enter the joint remains speculative. Δ indicates serotonin and ○, platelet microparticle. Professional illustration by Steve Moskowitz, Advanced Medical Graphics. See Figure 7 in the article by Cloutier et al that begins on page 1334.