Brain-immune interactions and ischemic stroke: clinical implications

Abstract

Increasing evidence shows that the central nervous system and the immune system interact in complex ways, and better insight into these interactions may be relevant to the treatment of patients with stroke and other forms of central nervous system injury. Atherosclerosis, autoimmune disease, and physiological stressors, such as infection or surgery, cause inflammation that contributes to vascular injury and increases the risk of stroke. In addition, the immune system actively participates in the acute pathogenesis of stroke. Thrombosis and hypoxia trigger an intravascular inflammatory cascade, which is further augmented by the innate immune response to cellular damage occurring in the parenchyma. This immune activation may cause secondary tissue injury, but it is unclear whether modulating the acute immune response to stroke can produce clinical benefits. Attempts to dampen immune activation after stroke may have adverse effects because central nervous system injury causes significant immunodepression that places patients at higher risk of infections, such as pneumonia. The activation of innate immunity after stroke sets the stage for an adaptive immune response directed against brain antigens. The pathogenic significance of adaptive immunity and its long-term effects on the postischemic brain remains unclear, but it cannot be ruled out that a persistent autoimmune response to brain antigens has deleterious and long-lasting consequences. Further research will be required to determine what role, if any, immunity has in long-term outcomes after stroke, but elucidation of potential mechanisms may open promising avenues for the development of new therapeutics to improve neurological recovery after brain injury.

Figure

Progression of inflammation and immune activation in the development of stroke. Chronic inflammation from atherosclerosis, autoimmune disease, and physiological stress results in progressive vascular injury that increases the risk of stroke. Acute occlusion of the cerebral vasculature produces intravascular hypoxia that triggers a rapid inflammatory response. As tissue damage proceeds, cellular components activate the innate immune response and set the stage for the engagement of adaptive immunity. Questions remain about whether this immune activation after stroke causes autoimmunity that affects neurological recovery. CNS indicates central nervous system; LDL, low-density lipoprotein.