Central nervous system (CNS)-infiltrating lymphocytes contribute to the progression of cerebral infarction in ischemic stroke. The damaged brain, in turn, exerts suppressive effects on the immune system. The temporal relationship of this reciprocal interaction between immune system and ischemic brain has not been defined, making immune intervention to limit brain damage exceedingly difficult. Moreover, the high prevalence of infection in stroke patients requires a better understanding of how stroke influences immune responses systemically and within the brain, to combat immune-related post-stroke complications. We recently showed that natural killer (NK) cells - a critical component of the innate immune system - are abundantly represented in peri-infarcted area of brain sections from autopsies of stroke patients. In a mouse model of cerebral ischemia, we showed that ischemic neuron-derived fractalkine recruited NK cells, which could accelerate brain infarction in the acute stage of ischemic stroke. Subsequently, NK cells exhibited decreased frequency and compromised function. Those NK cells expressed neurotransmitter receptors, and their exposure to acetylcholine impaired function. Based on these findings, we hypothesize that the physical proximity of ischemic neurons and NK cells in the CNS, as well as different neuronal signals received by NK cells within the CNS and the peripheral lymphoid organs, underlie the differential mechanisms responsible for NK cell deficiency in the periphery and in the brain. This would lead to NK cell-associated immune deficiency that favors the development of infection and post-stroke complications. To test this hypothesis, we will analyze the pathways that lead to NK cell deficiency in stroke, and relate those findings to clinical outcomes.
The specific aims are: 1) To define the temporal events associated with functional changes in NK cells from competency to deficiency, and to identify the characteristics acquired by NK cells in the periphery and in the CNS after brain ischemia; 2) To identify the mechanisms responsible for NK cell deficiency in the periphery and in the CNS after brain ischemia; 3) To investigate the clinical relevance of NK cell deficiency on infection in stroke, and to test strategies of manipulation of NK cell deficiency for the reduction of post-stroke infection. In all, this proposa will advance the understanding of key neuroimmune interactions that might allow design of strategies of NK cell-based intervention as a new tool limiting risks of post-stroke infection.

Public Health Relevance

are major complications in stroke patients, and often lead to sustained disability and/or elevated mortality rate in those patients. The inhibition of immunity after brain cessation of blood supply has been recongnized as a central cause of infection in stroke patients. However, since the mechanisms involved in the process are not known, attempts to reverse stroke-associated immune deficiency is both problematic and non- specific. Natural killer (NK) cells are immune cells that are recruited as first barrier to fight pathogens, and orchestrate protective activities at the level of both the innate and adaptive immune systems. During ischemic stroke, NK cells become significantly impaired and reduced in number. In this project, we will dissect how ischemic brain injury leads to NK cell deficiency, to better understand the interplay between the immune and nervous systems after brain ischemia. Importantly, we will also test new strategies to manipulate NK cells as a new approach to improve host immune defenses in post-stroke patients.

National Institute of Health (NIH)
National Institute of Neurological Disorders and Stroke (NINDS)
Research Project (R01)
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Acute Neural Injury and Epilepsy Study Section (ANIE)
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Bosetti, Francesca
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St. Joseph's Hospital and Medical Center
United States
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