ICAM1 and diabetes mellitus: A central and causal role of adherent leukocytes in vascular damage in DR—which is related to an increased expression of ICAM 1 and CD 18—results in increased numbers of leukocytes in retinal vasculature of diabetic humans and in animal work has been shown to begin as early as 1 week following experimental diabetes onset and results in injury to the endothelium via a Fas ligand (FasL)—mediated mechanism; a process which leads to breakdown of the BRB (Joussen et al., 2004).