APOE and atherosclerosis: Hematopoietic deletion of the complementary receptor CD27 in Apoe–/– mice correspondingly increased atherosclerosis, but this was attributed to a reduction in atheroprotective TREG cells.78 While B-cell costimulatory molecule interactions with TREG and effector T cells may be important in atherosclerosis, both GITR and CD27 are also expressed on TFH cells and their role here is largely unexplored.