S1PR1 and stroke disorder: Contributing events, such as inflammation at the stroke site, allowing E-selectin to be expressed by the inflamed endothelium, S1P2 to reduce the extent of tight junctions established by S1P1, and L-selectin expression on activated lymphocytes may all contribute towards TH and TREG cell rolling and diapedesis through vessels traversing cerebral areas possessing S1PHIGH concentrations.