CTLA4 and Stroke: At later time-points, i.e., 24–48 h after stroke, the primary pathway expressed in the peripheral blood of stroke patients relies on cytotoxic T-lymphocyte antigen 4 (CTLA4) (Barr et al., 2015), a costimulatory molecule expressed by activated T cells that serves as a negative modulator of adaptive immune cell functions (Buchbinder and Hodi, 2015).