Potential specific immunological indicators for stroke associated infection are partly modulated by sympathetic pathway activation

Targeting brain-peripheral immune responses for secondary brain injury after ischemic and hemorrhagic stroke

The notion that the central nervous system is an immunologically immune-exempt organ has changed over the past two decades, with increasing evidence of strong links and interactions between the central nervous system and the peripheral immune system, both in the healthy state and after ischemic and hemorrhagic stroke. Although primary injury after stroke is certainly important, the limited therapeutic efficacy, poor neurological prognosis and high mortality have led researchers to realize that secondary injury and damage may also play important roles in influencing long-term neurological prognosis and mortality and that the neuroinflammatory process in secondary injury is one of the most important influences on disease progression. Here, we summarize the interactions of the central nervous system with the peripheral immune system after ischemic and hemorrhagic stroke, in particular, how the central nervous system activates and recruits peripheral immune components, and we review recent advances in corresponding therapeutic approaches and clinical studies, emphasizing the importance of the role of the peripheral immune system in ischemic and hemorrhagic stroke.

Exploring the Utility of Autonomic Nervous System Evaluation for Stroke Prognosis

Stroke is a major cause of functional disability and is increasing in frequency. Therefore, stroke prognosis must be both accurate and timely. Among other biomarkers, heart rate variability (HRV) is investigated in terms of prognostic accuracy within stroke patients. The literature research of two databases (MEDLINE and Scopus) is performed to trace all relevant studies published within the last decade addressing the potential utility of HRV for stroke prognosis. Only the full-text articles published in English are included. In total, forty-five articles have been traced and are included in the present review. The prognostic value of biomarkers of autonomic dysfunction (AD) in terms of mortality, neurological deterioration, and functional outcome appears to be within the range of known clinical variables, highlighting their utility as prognostic tools. Moreover, they may provide additional information regarding poststroke infections, depression, and cardiac adverse events. AD biomarkers have demonstrated their utility not only in the setting of acute ischemic stroke but also in transient ischemic attack, intracerebral hemorrhage, and traumatic brain injury, thus representing a promising prognostic tool whose clinical application may greatly facilitate individualized stroke care.

Interactions between the Autonomic Nervous System and the Immune System after Stroke

Acute stroke is one of the leading causes of morbidity and mortality worldwide. Stroke-induced immune-inflammatory response occurs in the perilesion areas and the periphery. Although stroke-induced immunosuppression may alleviate brain injury, it hinders brain repair as the immune-inflammatory response plays a bidirectional role after acute stroke. Furthermore, suppression of the systemic immune-inflammatory response increases the risk of life-threatening systemic bacterial infections after acute stroke. Therefore, it is essential to explore the mechanisms that underlie the stroke-induced immune-inflammatory response. Autonomic nervous system (ANS) activation is critical for regulating the local and systemic immune-inflammatory responses and may influence the prognosis of acute stroke. We review the changes in the sympathetic and parasympathetic nervous systems and their influence on the immune-inflammatory response after stroke. Importantly, this article summarizes the mechanisms on how ANS regulates the immune-inflammatory response through neurotransmitters and their receptors in immunocytes and immune organs after stroke. To facilitate translational research, we also discuss the promising therapeutic approaches modulating the activation of the ANS or the immune-inflammatory response to promote neurologic recovery after stroke. © 2022 American Physiological Society. Compr Physiol 12:3665-3704, 2022.

MicroRNA-4443 regulates monocyte activation by targeting tumor necrosis factor receptor associated factor 4 in stroke-induced immunosuppression

BACKGROUND AND PURPOSE

MicroRNAs (miRNAs) have been demonstrated to play crucial roles in the early stage of acute ischaemic stroke (AIS). The purpose of this study was to investigate the expression patterns of miRNAs in peripheral blood mononuclear cells (PBMCs) from AIS patients and further explore related molecular mechanisms in stroke-induced immunodeficiency syndrome (SIDS).

METHODS

The miRNA expression patterns of PBMCs were detected by miRNA microarray and validated by quantitative real-time polymerase chain reaction (qRT-PCR) in AIS patients and healthy controls. Bioinformatics methods and luciferase reporter assays were used to detect the downstream target genes. Following stimulation with lipopolysaccharide and interleukin-4, the expression of miR-4443, tumor necrosis factor receptor associated factor 4 (TRAF4) and the nuclear factor kappa B (NF-κB) pathway were evaluated. Furthermore, transfection with miR-4443 mimic or inhibitor in the monocytes was carried out to gain insight into the mechanisms in SIDS.

RESULTS

Interleukin-10 in AIS patients was significantly higher than that of healthy controls. The miRNA microarray analysis and qRTPCR validation showed that only miR-4443 was upregulated expressed in PBMCs from AIS patients, especially in monocytes. miR-4443 was shown to directly interact with the 3' untranslated regions of TRAF4, resulting in suppression of TRAF4 protein expression. Furthermore, the expression of miR-4443 and TRAF4 was regulated by stimulation with lipopolysaccharide or interleukin-4. Additionally, overexpression of miR-4443 suppressed the TRAF4/Iκα/NF-κB signaling pathway to activate the expression of anti-inflammatory cytokines in monocytes.

CONCLUSIONS

The increased expression of miR-4443 induced monocyte dysfunction by targeting TRAF4, which may function as a crucial mediator in SIDS.

Predictors of urinary tract infection in acute stroke patients: A cohort study

Patients with stroke have a high risk of infection which may be predicted by age, procalcitonin, interleukin-6, C-reactive protein, National Institute of Health stroke scale (NHSS) score, diabetes, etc. These prediction methods can reduce unfavourable outcome by preventing the occurrence of infection.We aim to identify early predictors for urinary tract infection in patients after stroke.In 186 collected acute stroke patients, we divided them into urinary tract infection group, other infection type groups, and non-infected group. Data were recorded at admission. Independent risk factors and infection prediction model were determined using Logistic regression analyses. Likelihood ratio test was used to detect the prediction effect of the model. Receiver operating characteristic curve and the corresponding area under the curve were used to measure the predictive accuracy of indicators for urinary tract infection.Of the 186 subjects, there were 35 cases of urinary tract infection. Elevated interleukin-6, higher NIHSS, and decreased hemoglobin may be used to predict urinary tract infection. And the predictive model for urinary tract infection (including sex, NIHSS, interleukin-6, and hemoglobin) have the best predictive effect.This study is the first to discover that decreased hemoglobin at admission may predict urinary tract infection. The prediction model shows the best accuracy.

NK cells in cerebral ischemia

As a vital cell type in immune system and infiltrating cells in ischemic brain, NK cells can bridge the crosstalk between immune system and nervous system in stroke setting. The mechanism of action of NK cells is complicated, involving direct and indirect actions. NK cells are closely associated with poststroke inflammation, immunodepression and infections. The excessive inflammatory response in ischemic brain is one of the important causes for aggravating cerebral ischemic injury. Besides the inflammation induced by ischemia itself, thrombolytic drug tissue plasminogen activator (tPA) administration could also induce deteriorative inflammation, which is unfavorable for stroke control and recovery. Regulating NK cells may has the potential to modulate the immune response, limiting the development of ischemic damage and getting better outcome. In addition, post-stroke immunosuppression may lead to infections which contribute to higher severity and mortality of ischemic stroke (IS). Targeting NK cells may help to find novel pathways for IS therapy, which can both ameliorate the infarction itself, but also reduce the infectious complications. NK cells may also link IS and related diseases, suggesting NK cells can be used as a diagnostic or prognostic biomarker for IS prevention and treatment.

Complex interplay of multiple biological systems that contribute to post-stroke infections

Stroke is a leading contributor of death and disability around the world. Despite its recognised debilitating neurological deficits, a devastating clinical complication of surviving stroke patients that needs more attention is infection. Up to half of the patients develop infections after stroke, and a high proportion of them will die as a direct consequence. Major clinical trials that examined preventive antibiotic therapy in stroke patients have demonstrated this method of prevention is not effective as it does not reduce incidence of post-stroke pneumonia or improve patient outcome. Additionally, retrospective studies evaluating the use of β-blockers for the modulation of the sympathetic nervous system to prevent post-stroke infections have given mixed results. Therefore, there is an urgent need for more effective therapeutic options that target the underlying mechanisms of post-stroke infections. The understanding that infections are largely attributable to the "stroke-induced systemic immunosuppression" phenomenon has begun to emerge, and thus, exploring the pathways that trigger post-stroke immunosuppression is expected to reveal potential new therapeutics. As such, we will outline the impacts that stroke has on several biological systems in this review, and discuss how these contribute to host susceptibility to infection after stroke. Furthermore, the emerging role of the gut and its microbiota has recently come to surface and intensifies the complex pathways to post-stroke infection. Finally, we identify potential avenues to combat infection that target the pathways of stroke-induced systemic immunosuppression to ultimately improve stroke patient outcome.

Blood Glutamate Levels Are Closely Related to Acute Lung Injury and Prognosis after Stroke

Background

Acute lung injury (ALI) is a serious complication of stroke that occurs with a high incidence. Our preclinical results indicated that ALI might be related to blood glutamate levels after brain injury. The purpose of this study was to assess dynamic changes in blood glutamate levels in patients with stroke and to determine the correlation between blood glutamate levels, ALI, and long-term prognosis after stroke.

Methods

Venous blood samples were collected from controls and patients with stroke at admission and on the third and seventh day after the onset of stroke. Patients were followed for 3 months. The correlations among blood glutamate levels, severities of stroke and ALI, and long-term outcomes were analyzed, and the predictive values of blood glutamate levels and severity scores for ALI were assessed.

Results

In this study, a total of 384 patients with stroke were enrolled, with a median age of 59 years. Patients showed significantly increased blood glutamate levels within 7 days of stroke onset (p < 0.05), and patients with more severe injuries showed higher blood glutamate levels. Moreover, blood glutamate levels were closely related to the occurrence (adjusted odds ratio, 3.022, p = 0.003) and severity (p < 0.001) of ALI and the long-term prognosis after stroke (p < 0.05), and they were a more accurate predictor of ALI than the more commonly used severity scores (p < 0.01).

Conclusion

These results indicated that an increased blood glutamate level was closely related to the development of ALI and a poor prognosis after stroke.

Clinical Trial Registration

http://www.chictr.org.cn, identifier ChiCTR-RPC-15006770.