Arterial thromboembolism is initiated by hemostatic thrombus formation. Injured endothelium, exposure of subendothelial collagen I, and local concentration of hemostatic factors that bind to platelet surface receptors trigger their shape change, adherence, and activation. Both Ig-ITIM receptors CEACAM1 and CEACAM2 negatively regulate platelet-collagen I interactions, attenuate platelet activation, and attenuate thrombus growth and stability in vitro and in vivo.^1,7  Professional illustration by Patrick Lane, ScEYEnce Studios.