CXCR4 and Stroke: Overall, T and B cells exhibit strong circadian oscillations in the blood which are linked with oscillations in CXCR4 and CX3CR1 expression, regulated by glucocorticoids and catecholamines as well as hypoxia-inducible factor 1α signaling 44, which in turn contribute to development and severity of stroke, recovery from stroke, and neuronal protection after brain injury 44,53.