CLDN5 and ischemia: The data indicate that IVIg provides a two-way protective mechanism for cerebral endothelial cells, firstly by blocking the increase in BBB permeability involving downregulation of tight-junction proteins claudin 5 and occludin, and secondly by preventing ischemia-induced endothelial cell death involving a reduction in anti-apoptotic proteins, Bcl-2 and Bcl-XL.