CD28 and ischemic stroke: Subjects with acute ischemic stroke had a significantly higher peripheral frequency of CD4+ cells compared to controls without acute ischemic stroke (51.4 ± 6.8% vs 34.4 ± 6.4%; P = 0.0001); similarly, ischemic stroke subjects had a significantly higher peripheral frequency of CD4+CD28− cells compared to controls without acute ischemic stroke (5.7 ± 2.4% vs 2.8 ± 0.9%; P = 0.0001).