Chronic Alterations in Systemic Immune Function after Traumatic Brain Injury

Association Between Ocular Trauma and Activation of Ocular Toxoplasmosis

PURPOSE

To evaluate the association between ocular trauma and activation of ocular toxoplasmosis.

METHODS

Retrospective review of 686 patients with ocular toxoplasmosis and its association with trauma to the eye or the head within 1 week of activation.

RESULTS

Ten patients with a history of trauma and activation of ocular toxoplasmosis were detected (10/686; 1.45%). Nine patients showed a primary focus of retinitis without a previous scar and one patient had a recurrent form of ocular toxoplasmosis. From these 10 patients, Toxoplasma IgG was positive in eight of them. The median age of the patients was 35.8 years-old (range 17 to 65).

CONCLUSIONS

These cases suggest that trauma can be associated with activation of retinal bradyzoite cysts in ocular toxoplasmosis.

'Comprehensive review of emerging drug targets in traumatic brain injury (TBI): challenges and future scope

Traumatic brain injury (TBI) is a complex brain problem that causes significant morbidity and mortality among people of all age groups. The complex pathophysiology, varied symptoms, and inadequate treatment further precipitate the problem. Further, TBI produces several psychiatric problems and other related complications in post-TBI survival patients, which are often treated symptomatically or inadequately. Several approaches, including neuroprotective agents targeting several pathways of oxidative stress, neuroinflammation, cytokines, immune system GABA, glutamatergic, microglia, and astrocytes, are being tried by researchers to develop effective treatments or magic bullets to manage the condition effectively. The problem of TBI is therefore treated as a challenge among pharmaceutical scientists or researchers to develop drugs for the effective management of this problem. The goal of the present comprehensive review is to provide an overview of the several pharmacological targets, processes, and cellular pathways that researchers are focusing on, along with an update on their current state.

Applying Dynamical Systems Theory to Improve Personalized Medicine Following Mild Traumatic Brain Injury

A sizable proportion of patients with mild traumatic brain injury (mTBI) have persistent symptoms and functional impairments months to years following injury. This phenomenon is continually observed despite an explosion of research and interest in improving mTBI clinical outcomes over the last two decades. All pharmacological clinical trials to date have failed to demonstrate improved outcomes for mTBI. One possible explanation for these continued failures is an overly myopic approach to treating mTBI (i.e., testing the effect of a single drug with a specific mechanism on a group of people with highly heterogenous injuries). Clinical presentation and prognosis of mTBI vary considerably between patients, and yet we continue to assess group-level effects of a homogenized treatment. We need to utilize an equally complex treatment approach to match the extraordinary complexity of the human brain. Dynamical systems theory has been used to describe systems composed of multiple subsystems who function somewhat independently but are ultimately interconnected. This theory was popularized in the motor control literature as an overarching framework for how the mind and body connect to interact and move through the environment. However, the human body can be viewed as a dynamical system composed of multiple subsystems (i.e., organ systems) who have isolated functions, which are also codependent on the health and performance of other interconnected organ systems. In this perspective piece, we will use the example of mTBI in the obese patient to demonstrate how broadening our approach to treatment of the individual (and not necessarily the injury) may ultimately yield improved outcomes. Furthermore, we will explore clinical and pre-clinical evidence demonstrating multiple system interactions in the context of obesity and TBI and discuss how expanding our understanding of the mechanistic interplay between multiple organ systems may ultimately provide a more personalized treatment approach for this mTBI patient subpopulation.

Bradykinin 2 Receptors Mediate Long-Term Neurocognitive Deficits After Experimental Traumatic Brain Injury

The kallikrein-kinin system is one of the first inflammatory pathways to be activated following traumatic brain injury (TBI) and has been shown to exacerbate brain edema formation in the acute phase through activation of bradykinin 2 receptors (B2R). However, the influence of B2R on chronic post-traumatic damage and outcome is unclear. In the current study, we assessed long-term effects of B2R-knockout (KO) after experimental TBI. B2R KO mice (heterozygous, homozygous) and wild-type (WT) littermates (n = 10/group) were subjected to controlled cortical impact (CCI) TBI. Lesion size was evaluated by magnetic resonance imaging up to 90 days after CCI. Motor and memory function were regularly assessed by Neurological Severity Score, Beam Walk, and Barnes maze test. Ninety days after TBI, brains were harvested for immunohistochemical analysis. There was no difference in cortical lesion size between B2R-deficient and WT animals 3 months after injury; however, hippocampal damage was reduced in B2R KO mice (p = 0.03). Protection of hippocampal tissue was accompanied by a significant improvement of learning and memory function 3 months after TBI (p = 0.02 WT vs. KO), whereas motor function was not influenced. Scar formation and astrogliosis were unaffected, but B2R deficiency led to a gene-dose-dependent attenuation of microglial activation and a reduction of CD45+ cells 3 months after TBI in cortex (p = 0.0003) and hippocampus (p < 0.0001). These results suggest that chronic hippocampal neurodegeneration and subsequent cognitive impairment are mediated by prolonged neuroinflammation and B2R. Inhibition of B2R may therefore represent a novel strategy to reduce long-term neurocognitive deficits after TBI.

Single episode of moderate to severe traumatic brain injury leads to chronic neurological deficits and Alzheimer's-like pathological dementia

Traumatic brain injury (TBI) is one of the foremost causes of disability and mortality globally. While the scientific and medical emphasis is to save lives and avoid disability during acute period of injury, a severe health problem can manifest years after injury. For instance, TBI increases the risk of cognitive impairment in the elderly. Remote TBI history was reported to be a cause of the accelerated clinical trajectory of Alzheimer's disease-related dementia (ADRD) resulting in earlier onset of cognitive impairment and increased AD-associated pathological markers like greater amyloid deposition and cortical thinning. It is not well understood whether a single TBI event may increase the risk of dementia. Moreover, the cellular signaling pathways remain elusive for the chronic effects of TBI on cognition. We have hypothesized that a single TBI induces sustained neuroinflammation and disrupts cellular communication in a way that results later in ADRD pathology. To test this, we induced TBI in young adult CD1 mice and assessed the behavioral outcomes after 11 months followed by pathological, histological, transcriptomic, and MRI assessment. On MRI scans, these mice showed significant loss of tissue, reduced CBF, and higher white matter injury compared to sham mice. We found these brains showed progressive atrophy, markers of ADRD, sustained astrogliosis, loss of neuronal plasticity, and growth factors even after 1-year post-TBI. Because of progressive neurodegeneration, these mice had motor deficits, showed cognitive impairments, and wandered randomly in open field. We, therefore, conclude that progressive pathology after adulthood TBI leads to neurodegenerative conditions such as ADRD and impairs neuronal functions.

Dysregulated brain-gut axis in the setting of traumatic brain injury: review of mechanisms and anti-inflammatory pharmacotherapies

Traumatic brain injury (TBI) is a chronic and debilitating disease, associated with a high risk of psychiatric and neurodegenerative diseases. Despite significant advancements in improving outcomes, the lack of effective treatments underscore the urgent need for innovative therapeutic strategies. The brain-gut axis has emerged as a crucial bidirectional pathway connecting the brain and the gastrointestinal (GI) system through an intricate network of neuronal, hormonal, and immunological pathways. Four main pathways are primarily implicated in this crosstalk, including the systemic immune system, autonomic and enteric nervous systems, neuroendocrine system, and microbiome. TBI induces profound changes in the gut, initiating an unrestrained vicious cycle that exacerbates brain injury through the brain-gut axis. Alterations in the gut include mucosal damage associated with the malabsorption of nutrients/electrolytes, disintegration of the intestinal barrier, increased infiltration of systemic immune cells, dysmotility, dysbiosis, enteroendocrine cell (EEC) dysfunction and disruption in the enteric nervous system (ENS) and autonomic nervous system (ANS). Collectively, these changes further contribute to brain neuroinflammation and neurodegeneration via the gut-brain axis. In this review article, we elucidate the roles of various anti-inflammatory pharmacotherapies capable of attenuating the dysregulated inflammatory response along the brain-gut axis in TBI. These agents include hormones such as serotonin, ghrelin, and progesterone, ANS regulators such as beta-blockers, lipid-lowering drugs like statins, and intestinal flora modulators such as probiotics and antibiotics. They attenuate neuroinflammation by targeting distinct inflammatory pathways in both the brain and the gut post-TBI. These therapeutic agents exhibit promising potential in mitigating inflammation along the brain-gut axis and enhancing neurocognitive outcomes for TBI patients.

Modelling lung infection with Klebsiella pneumoniae after murine traumatic brain injury

Pneumonia is a common comorbidity in patients with severe traumatic brain injury (TBI), and is associated with increased morbidity and mortality. In this study, we established a model of intratracheal Klebsiella pneumoniae administration in young adult male and female mice, at 4 days following an experimental TBI, to investigate how K. pneumoniae infection influences acute post-TBI outcomes. A dose-response curve determined the optimal dose of K. pneumoniae for inoculation (1 x 10^6 colony forming units), and administration at 4 days post-TBI resulted in transient body weight loss and sickness behaviors (hypoactivity and acute dyspnea). K. pneumoniae infection led to an increase in pro-inflammatory cytokines in serum and bronchoalveolar lavage fluid at 24 h post-infection, in both TBI and sham (uninjured) mice. By 7 days, when myeloperoxidase + neutrophil numbers had returned to baseline in all groups, lung histopathology was observed with an increase in airspace size in TBI + K. pneumoniae mice compared to TBI + vehicle mice. In the brain, increased neuroinflammatory gene expression was observed acutely in response to TBI, with an exacerbated increase in Ccl2 and Hmox1 in TBI + K. pneumoniae mice compared to either TBI or K. pneumoniae alone. However, the presence of neuroinflammatory immune cells in the injured brain, and the extent of damage to cortical and hippocampal brain tissue, was comparable between K. pneumoniae and vehicle-treated mice by 7 days. Examination of the fecal microbiome across a time course did not reveal any pronounced effects of either injury or K. pneumoniae on bacterial diversity or abundance. Together, these findings demonstrate that K. pneumoniae lung infection after TBI induces an acute and transient inflammatory response, primarily localized to the lungs with some systemic effects. However, this infection had minimal impact on secondary injury processes in the brain following TBI. Future studies are needed to evaluate the potential longer-term consequences of this dual-hit insult.

Cerebral and Peripheral Immune Cell Changes following Rodent Juvenile Traumatic Brain Injury

Traumatic brain injury (TBI) is one of the leading causes of death and disability. TBI is associated with neuroinflammation, but temporal changes in immune and inflammatory signaling following TBI have not been fully elucidated. Furthermore, there have been no previous studies on changes in immune cell populations following TBI via the Closed Head Injury Model of Engineered Rotational Acceleration (CHIMERA). The current study aimed to determine the time course changes to inflammatory marker mRNA expression in the acute period following TBI in juvenile rats and to determine acute changes to brain and circulating immune cell populations. For this study, post-natal day (PND)-30 male Long Evans rats sustained a TBI or Sham TBI and were euthanized at 0, 3, 6, 12, 24, or 96 h post-injury. Prefrontal cortex and hippocampus samples were used to determine mRNA expression changes of inflammatory factors. The mRNA expression of the pro-inflammatory cytokine TNF-α was significantly elevated at 6 h post-injury in both regions evaluated. To evaluate immune cell populations, male Long Evans rats were euthanized at 48 h post-injury, and brain and blood samples were used for cell sorting by marker-specific antibodies. In the peripheral blood, there was an elevation in CD3+ total T cells, CD45R+ total B cells, and CD3+CD4+ helper T cells in the TBI subjects. However, there were no changes to natural killer cells or CD3+CD8+ cytotoxic T cell populations. In the brain, there was a reduction in CD11b/c+ monocytes/macrophages, but no changes in other immune cell populations. At 48 h post-injury, the TBI subjects also demonstrated expansion of the thymic medulla. These changes in the cerebral and blood immune cell populations and thymic medulla expansion may implicate the subacute recovery timeframe as a vulnerable window for the immune system in the pediatric population.

Bi-directional neuro-immune dysfunction after chronic experimental brain injury

BACKGROUND

It is well established that traumatic brain injury (TBI) causes acute and chronic alterations in systemic immune function and that systemic immune changes contribute to posttraumatic neuroinflammation and neurodegeneration. However, how TBI affects bone marrow (BM) hematopoietic stem/progenitor cells chronically and to what extent such changes may negatively impact innate immunity and neurological function has not been examined.

METHODS

To further understand the role of BM cell derivatives on TBI outcome, we generated BM chimeric mice by transplanting BM from chronically injured or sham (i.e., 90 days post-surgery) congenic donor mice into otherwise healthy, age-matched, irradiated CD45.2 C57BL/6 (WT) hosts. Immune changes were evaluated by flow cytometry, multiplex ELISA, and NanoString technology. Moderate-to-severe TBI was induced by controlled cortical impact injury and neurological function was measured using a battery of behavioral tests.

RESULTS

TBI induced chronic alterations in the transcriptome of BM lineage-c-Kit+Sca1+ (LSK+) cells in C57BL/6 mice, including modified epigenetic and senescence pathways. After 8 weeks of reconstitution, peripheral myeloid cells from TBI→WT mice showed significantly higher oxidative stress levels and reduced phagocytic activity. At eight months after reconstitution, TBI→WT chimeric mice were leukopenic, with continued alterations in phagocytosis and oxidative stress responses, as well as persistent neurological deficits. Gene expression analysis revealed BM-driven changes in neuroinflammation and neuropathology after 8 weeks and 8 months of reconstitution, respectively. Chimeric mice subjected to TBI at 8 weeks and 8 months post-reconstitution showed that longer reconstitution periods (i.e., time post-injury) were associated with increased microgliosis and leukocyte infiltration. Pre-treatment with a senolytic agent, ABT-263, significantly improved behavioral performance of aged C57BL/6 mice at baseline, although it did not attenuate neuroinflammation in the acutely injured brain.

CONCLUSIONS

TBI causes chronic activation and progressive dysfunction of the BM stem/progenitor cell pool, which drives long-term deficits in hematopoiesis, innate immunity, and neurological function, as well as altered sensitivity to subsequent brain injury.

Experimental Models of Hospital-Acquired Infections After Traumatic Brain Injury: Challenges and Opportunities

Patients hospitalized after a moderate or severe traumatic brain injury (TBI) are at increased risk of nosocomial infections, including bacterial pneumonia and other upper respiratory tract infections. Infections represent a secondary immune challenge for vulnerable TBI patients that can lead to increased morbidity and poorer long-term prognosis. This review first describes the clinical significance of infections after TBI, delving into the known mechanisms by which a TBI can alter systemic immunological responses towards an immunosuppressive state, leading to promotion of increased vulnerability to infections. Pulmonary dysfunction resulting from respiratory tract infections is considered in the context of neurotrauma, including the bidirectional relationship between the brain and lungs. Turning to pre-clinical modeling, current laboratory approaches to study experimental TBI and lung infections are reviewed, to highlight findings from the limited key studies to date that have incorporated both insults. Then, practical decisions for the experimental design of animal studies of post-injury infections are discussed. Variables associated with the host animal, the infectious agent (e.g., species, strain, dose, and administration route), as well as the timing of the infection relative to the injury model are important considerations for model development. Together, the purpose of this review is to highlight the significant clinical need for increased pre-clinical research into the two-hit insult of a hospital-acquired infection after TBI to encourage further scientific enquiry in the field.

Neurobehavioral and inflammatory responses following traumatic brain injury in male and female mice

Traumatic brain injury (TBI) is a leading cause of mortality and is associated with a high rate of functional comorbidities, including motor, cognitive, anxiety, depression, and emotional disorders. TBI pathophysiology and recovery are complicated and involve several mechanistic pathways that control neurobehavioral outcomes. In this study, male and female C57Bl/6 J mice were subjected to a controlled cortical impact model of TBI or sham injury and evaluated for different neurobehavioral and inflammatory outcomes over a month. We demonstrate that TBI mice have increased motor dysfunction at early and late time points following the injury as compared to the sham group. Anxiety-like symptoms were time- and task-dependent, with both sexes having increased anxiety-like behavior 2 weeks post-injury. Cognitive functions measured by T-maze presented greater deficits in TBI mice, while there was no sex or injury-related difference in depressive-like behaviors. Notably, a significant effect of sex was found in empathy-like behavior, with females showing more allogrooming and freezing behavior in the consoling and fear observational tests, respectively. Evaluating the impact of the injury-induced brain damage demonstrated a greater injury volume and neuronal degeneration in males compared to females one month after TBI. Moreover, male mice showed higher peripheral inflammatory responses, as represented by elevated serum levels of peripheral leukocytes and inflammatory markers. These results will have significant implications for understanding TBI's long-term consequences on neurobehavioral and inflammatory responses, which are sex-specific and can be considered for individualized therapeutic strategies in treating TBI.

Single-cell transcriptomics of human traumatic brain injury reveals activation of endogenous retroviruses in oligodendroglia

Traumatic brain injury (TBI) is a leading cause of chronic brain impairment and results in a robust, but poorly understood, neuroinflammatory response that contributes to the long-term pathology. We used single-nuclei RNA sequencing (snRNA-seq) to study transcriptomic changes in different cell populations in human brain tissue obtained acutely after severe, life-threatening TBI. This revealed a unique transcriptional response in oligodendrocyte precursors and mature oligodendrocytes, including the activation of a robust innate immune response, indicating an important role for oligodendroglia in the initiation of neuroinflammation. The activation of an innate immune response correlated with transcriptional upregulation of endogenous retroviruses in oligodendroglia. This observation was causally linked in vitro using human glial progenitors, implicating these ancient viral sequences in human neuroinflammation. In summary, this work provides insight into the initiating events of the neuroinflammatory response in TBI, which has therapeutic implications.

Construction and validation of a predictive model of pneumonia for ICU patients with traumatic brain injury (TBI)

The incidence of pneumonia in ICU patients with TBI is very high, seriously affecting the prognosis. This study aims to construct a predictive model for pneumonia in ICU patients with TBI and provide help for the prevention of TBI-related pneumonia.Clinical data of ICU patients with TBI were collected from the Medical Information Mart for Intensive Care (MIMIC)-IV database and hospital data. Variables were screened by lasso and multivariate logistic regression to construct a predictive nomogram model, verified in internal validation cohort and external validation cohort by receiver operator characteristic (ROC) curve, calibration curve and decision curve analysis (DCA).A total of 1850 ICU patients with TBI were enrolled in the study from the MIMIC-IV database, including 1298 in the training cohort and 552 in internal validation cohort. The external validation cohort included 240 ICU patients with TBI from hospital data. Nine variables were selected from the training cohort by lasso regression and multivariate logistic regression, and a pneumonia prediction nomogram was constructed. This nomogram has a high discrimination in training, internal validation and external validation cohorts (AUC = 0.857, 0.877, 0.836). The calibration curve and DCA showed that this nomogram had a high calibration and better clinical decision-making efficiency.The nomogram showed excellent discrimination and clinical utility to predict pneumonia, and could identify pneumonia high-risk patients early, thus providing personalised treatment strategies for ICU patients with TBI.

CD8+ T cells in brain injury and neurodegeneration

The interaction between the peripheral immune system and the brain is increasingly being recognized as an important layer of neuroimmune regulation and plays vital roles in brain homeostasis as well as neurological disorders. As an important population of T-cell lymphocytes, the roles of CD8+ T cells in infectious diseases and tumor immunity have been well established. Recently, increasing number of complex functions of CD8+ T cells in brain disorders have been revealed. However, an advanced summary and discussion of the functions and mechanisms of CD8+ T cells in brain injury and neurodegeneration are still lacking. Here, we described the differentiation and function of CD8+ T cells, reviewed the involvement of CD8+ T cells in the regulation of brain injury including stroke and traumatic brain injury and neurodegenerative diseases, such as Alzheimer's disease (AD) and Parkinson's disease (PD), and discussed therapeutic prospects and future study goals. Understanding these processes will promote the investigation of T-cell immunity in brain disorders and provide new intervention strategies for the treatment of brain injury and neurodegeneration.

Elevation of White Blood Cell Subtypes in Adult Trauma Patients with Stress-Induced Hyperglycemia

BACKGROUND

Blood immune cell subset alterations following trauma can indicate a patient's immune-inflammatory status. This research explored the influence of stress-induced hyperglycemia (SIH) on platelet counts and white blood cell (WBC) subtypes, including the derived indices of the monocyte-to-lymphocyte ratio (MLR), neutrophil-to-lymphocyte ratio (NLR), and platelet-to-lymphocyte ratio (PLR), in trauma patients.

METHODS

We studied 15,480 adult trauma patients admitted from 1 January 1998 to 31 December 2022. They were categorized into four groups: nondiabetic normoglycemia (NDN, n = 11,602), diabetic normoglycemia (DN, n = 1750), SIH (n = 716), and diabetic hyperglycemia (DH, n = 1412). A propensity score-matched cohort was formed after adjusting for age, sex, and comorbidities, allowing for comparing the WBC subtypes and platelet counts.

RESULTS

Patients with SIH exhibited significantly increased counts of monocytes, neutrophils, and lymphocytes in contrast to NDN patients. However, no significant rise in platelet counts was noted in the SIH group. There were no observed increases in these cell counts in either the DN or DH groups.

CONCLUSIONS

Our results demonstrated that trauma patients with SIH showed significantly higher counts of monocytes, neutrophils, and lymphocytes when compared to NDN patients, whereas the DN and DH groups remained unaffected. This underscores the profound association between SIH and elevated levels of specific WBC subtypes.

Traumatic brain injury-induced inflammatory changes in the olfactory bulb disrupt neuronal networks leading to olfactory dysfunction

Approximately 20-68% of traumatic brain injury (TBI) patients exhibit trauma-associated olfactory deficits (OD) which can compromise not only the quality of life but also cognitive and neuropsychiatric functions. However, few studies to date have examined the impact of experimental TBI on OD. The present study examined inflammation and neuronal dysfunction in the olfactory bulb (OB) and the underlying mechanisms associated with OD in male mice using a controlled cortical impact (CCI) model. TBI caused a rapid inflammatory response in the OB as early as 24 h post-injury, including elevated mRNA levels of proinflammatory cytokines, increased numbers of microglia and infiltrating myeloid cells, and increased IL1β and IL6 production in these cells. These changes were sustained for up to 90 days after TBI. Moreover, we observed significant upregulation of the voltage-gated proton channel Hv1 and NOX2 expression levels, which were predominantly localized in microglia/macrophages and accompanied by increased reactive oxygen species production. In vivo OB neuronal firing activities showed early neuronal hyperexcitation and later hypo-neuronal activity in both glomerular layer and mitral cell layer after TBI, which were improved in the absence of Hv1. In a battery of olfactory behavioral tests, WT/TBI mice displayed significant OD. In contrast, neither Hv1 KO/TBI nor NOX2 KO/TBI mice showed robust OD. Finally, seven days of intranasal delivery of a NOX2 inhibitor (NOX2ds-tat) ameliorated post-traumatic OD. Collectively, these findings highlight the importance of OB neuronal networks and its role in TBI-mediated OD. Thus, targeting Hv1/NOX2 may be a potential intervention for improving post-traumatic anosmia.

The brain-bone marrow axis and its implications for chronic traumatic brain injury

Traumatic brain injury (TBI) causes acute and chronic alterations in systemic immune function which contribute to posttraumatic neuroinflammation and neurodegeneration. However, how TBI affects bone marrow (BM) hematopoietic stem/progenitor cells chronically and to what extent such changes may negatively impact innate immunity and neurological function has not been examined. To further understand the role of BM cell derivatives on TBI outcome, we generated BM chimeric mice by transplanting BM from chronically injured or sham congenic donor mice into otherwise healthy, age-matched, irradiated hosts. After 8 weeks of reconstitution, peripheral myeloid cells from TBI→WT mice showed significantly higher oxidative stress levels and reduced phagocytic activity. At eight months after reconstitution, TBI→WT chimeric mice were leukopenic, with continued alterations in phagocytosis and oxidative stress responses, as well as persistent neurological deficits. Gene expression analysis revealed BM-driven changes in neuroinflammation and neuropathology after 8 weeks and 8 months of reconstitution, respectively. Chimeric mice subjected to TBI showed that longer reconstitution periods were associated with increased microgliosis and leukocyte infiltration. Thus, TBI causes chronic activation and progressive dysfunction of the BM stem/progenitor cell pool, which drives long-term deficits in innate immunity and neurological function, as well as altered sensitivity to subsequent brain injury.

Neurosteroid Receptor Modulators for Treating Traumatic Brain Injury

Traumatic brain injury (TBI) triggers wide-ranging pathology that impacts multiple biochemical and physiological systems, both inside and outside the brain. Functional recovery in patients is impeded by early onset brain edema, acute and chronic inflammation, delayed cell death, and neurovascular disruption. Drug treatments that target these deficits are under active development, but it seems likely that fully effective therapy may require interruption of the multiplicity of TBI-induced pathological processes either by a cocktail of drug treatments or a single pleiotropic drug. The complex and highly interconnected biochemical network embodied by the neurosteroid system offers multiple options for the research and development of pleiotropic drug treatments that may provide benefit for those who have suffered a TBI. This narrative review examines the neurosteroids and their signaling systems and proposes directions for their utility in the next stage of TBI drug research and development.

Single Versus Repetitive Traumatic Brain Injury: Current Knowledge on the Chronic Outcomes, Neuropathology and the Role of TDP-43 Proteinopathy

Traumatic brain injury (TBI) is one of the most important causes of death and disability in adults and thus an important public health problem. Following TBI, secondary pathophysiological processes develop over time and condition the development of different neurodegenerative entities. Previous studies suggest that neurobehavioral changes occurring after a single TBI are the basis for the development of Alzheimer's disease, while repetitive TBI is considered to be a contributing factor for chronic traumatic encephalopathy development. However, pathophysiological processes that determine the evolvement of a particular chronic entity are still unclear. Human post-mortem studies have found combinations of amyloid, tau, Lewi bodies, and TAR DNA-binding protein 43 (TDP-43) pathologies after both single and repetitive TBI. This review focuses on the pathological changes of TDP-43 after single and repetitive brain traumas. Numerous studies have shown that TDP-43 proteinopathy noticeably occurs after repetitive head trauma. A relatively small number of available preclinical research on single brain injury are not in complete agreement with the results from the human samples, which makes it difficult to draw specific conclusions. Also, as TBI is considered a heterogeneous type of injury, different experimental trauma models and injury intensities may cause differences in the cascade of secondary injury, which should be considered in future studies. Experimental and post-mortem studies of TDP-43 pathobiology should be carried out, preferably in the same laboratories, to determine its involvement in the development of neurodegenerative conditions after one and repetitive TBI, especially in the context of the development of new therapeutic options.

Systemic immune response in young and elderly patients after traumatic brain injury

BACKGROUND

Traumatic brain injury (TBI) is a leading cause of death and long-term disability worldwide. In addition to primary brain damage, systemic immune alterations occur, with evidence for dysregulated immune responses in aggravating TBI outcome and complications. However, immune dysfunction following TBI has been only partially understood, especially in the elderly who represent a substantial proportion of TBI patients and worst outcome. Therefore, we aimed to conduct an in-depth immunological characterization of TBI patients, by evaluating both adaptive (T and B lymphocytes) and innate (NK and monocytes) immune cells of peripheral blood mononuclear cells (PBMC) collected acutely (< 48 h) after TBI in young (18-45 yo) and elderly (> 65 yo) patients, compared to age-matched controls, and also the levels of inflammatory biomarkers.

RESULTS

Our data show that young respond differently than elderly to TBI, highlighting the immune unfavourable status of elderly compared to young patients. While in young only CD4 T lymphocytes are activated by TBI, in elderly both CD4 and CD8 T cells are affected, and are induced to differentiate into subtypes with low cytotoxic activity, such as central memory CD4 T cells and memory precursor effector CD8 T cells. Moreover, TBI enhances the frequency of subsets that have not been previously investigated in TBI, namely the double negative CD27- IgD- and CD38-CD24- B lymphocytes, and CD56dim CD16- NK cells, both in young and elderly patients. TBI reduces the production of pro-inflammatory cytokines TNF-α and IL-6, and the expression of HLA-DM, HLA-DR, CD86/B7-2 in monocytes, suggesting a compromised ability to drive a pro-inflammatory response and to efficiently act as antigen presenting cells.

CONCLUSIONS

We described the acute immunological response induced by TBI and its relation with injury severity, which could contribute to pathologic evolution and possibly outcome. The focus on age-related immunological differences could help design specific therapeutic interventions based on patients' characteristics.

Colony-Stimulating Factor-1 Receptor Inhibition Transiently Attenuated the Peripheral Immune Response to Experimental Traumatic Brain Injury

To investigate microglial mechanisms in central and peripheral inflammation after experimental traumatic brain injury (TBI), we inhibited the colony-stimulating factor-1 receptor (CSF-1R) with PLX5622 (PLX). We hypothesized that microglia depletion would attenuate central inflammation acutely with no effect on peripheral inflammation. After randomization, male mice (n = 105) were fed PLX or control diets (21 days) and then received midline fluid percussion injury or sham injury. Brain and blood were collected at 1, 3, or 7 days post-injury (DPI). Immune cell populations were quantified in the brain and blood by flow cytometry. Cytokines (interleukin [IL]-6, IL-1β, tumor necrosis factor-α, interferon-γ, IL-17A, and IL-10) were quantified in the blood using a multi-plex enzyme-linked immunosorbent assay. Data were analyzed using Bayesian multi-variate, multi-level models. PLX depleted microglia at all time points and reduced neutrophils in the brain at 7 DPI. PLX also depleted CD115+ monocytes, reduced myeloid cells, neutrophils, and Ly6Clow monocytes in blood, and elevated IL-6. TBI induced a central and peripheral immune response. TBI elevated leukocytes, microglia, and macrophages in the brain and elevated peripheral myeloid cells, neutrophils, Ly6Cint monocytes, and IL-1β in the blood. TBI lowered peripheral CD115+ and Ly6Clow monocytes in the blood. TBI PLX mice had fewer leukocytes and microglia in the brain at 1 DPI, with elevated neutrophils at 7 DPI compared to TBI mice on a control diet. TBI PLX mice also had fewer peripheral myeloid cells, CD115+, and Ly6Clow monocytes in the blood at 3 DPI, but elevated Ly6Chigh, Ly6Cint, and CD115+ monocyte populations at 7 DPI, compared to TBI mice on a control diet. TBI PLX mice had elevated proinflammatory cytokines and lower anti-inflammatory cytokines in the blood at 7 DPI compared to TBI mice on a control diet. CSF-1R inhibition reduced the immune response to TBI at 1 and 3 DPI, but elevated peripheral inflammation at 7 DPI.

Systemic immune derangements are shared across various CNS pathologies and reflect novel mechanisms of immune privilege

Background

The nervous and immune systems interact in a reciprocal manner, both under physiologic and pathologic conditions. Literature spanning various CNS pathologies including brain tumors, stroke, traumatic brain injury and de-myelinating diseases describes a number of associated systemic immunologic changes, particularly in the T-cell compartment. These immunologic changes include severe T-cell lymphopenia, lymphoid organ contraction, and T-cell sequestration within the bone marrow.

Methods

We performed an in-depth systematic review of the literature and discussed pathologies that involve brain insults and systemic immune derangements.

Conclusions

In this review, we propose that the same immunologic changes hereafter termed 'systemic immune derangements', are present across CNS pathologies and may represent a novel, systemic mechanism of immune privilege for the CNS. We further demonstrate that systemic immune derangements are transient when associated with isolated insults such as stroke and TBI but persist in the setting of chronic CNS insults such as brain tumors. Systemic immune derangements have vast implications for informed treatment modalities and outcomes of various neurologic pathologies.

Modifiable Innate Biology within the Gut–Brain Axis for Alzheimer’s Disease

Alzheimer’s disease (AD) is a prototypical inflammation-associated loss of cognitive function, with approximately 90% of the AD burden associated with invading myeloid cells controlling the function of the resident microglia. This indicates that the immune microenvironment has a pivotal role in the pathogenesis of the disease. Multiple peripheral stimuli, conditioned by complex and varied interactions between signals that stem at the intestinal level and neuroimmune processes, are involved in the progression and severity of AD. Conceivably, the targeting of critical innate immune signals and cells is achievable, influencing immune and metabolic health within the gut–brain axis. Considerable progress has been made, modulating many different metabolic and immune alterations that can drive AD development. However, non-pharmacological strategies targeting immunometabolic processes affecting neuroinflammation in AD treatment remain general and, at this point, are applied to all patients regardless of disease features. Despite these possibilities, improved knowledge of the relative contribution of the different innate immune cells and molecules comprising the chronically inflamed brain network to AD pathogenesis, and elucidation of the network hierarchy, are needed for planning potent preventive and/or therapeutic interventions. Moreover, an integrative perspective addressing transdisciplinary fields can significantly contribute to molecular pathological epidemiology, improving the health and quality of life of AD patients. This review is intended to gather modifiable immunometabolic processes based on their importance in the prevention and management of AD.

Orally Administered Brain Protein Combined With Probiotics Increases Treg Differentiation to Reduce Secondary Inflammatory Damage Following Craniocerebral Trauma

Craniocerebral trauma is caused by external forces that can have detrimental effects on the vasculature and adjacent nerve cells at the site. After the mechanical and structural primary injury, a complex series of secondary cascades of injury exacerbates brain damage and cognitive dysfunction following mechanical and structural primary injury. Disruption of the blood-brain barrier and exposure of brain proteins following craniocerebral trauma, recognition by the immune system triggering autoimmune attack, and excessive secondary inflammatory responses causing malignant brain swelling, cerebral edema, and subsequent brain cell apoptosis provide a new direction for the suppression of brain inflammatory responses in the treatment of craniocerebral trauma. We observed that CD4⁺T/CD8⁺T in peripheral blood T cells of craniocerebral trauma rats were significantly higher than those of normal rats, and the ratio of CD4⁺CD25⁺Foxp3 (Foxp3)⁺Regulatory T cell (Treg) was significantly lower than that of normal rats and caused increased secondary inflammation. We constructed a rat model of post-surgical brain injury and orally administered brain protein combined with probiotics, which was observed to significantly reduce CD4⁺T/CD8⁺T and induce T-cell differentiation into CD4⁺CD25⁺Foxp3⁺Treg, thus, reducing secondary inflammatory responses following craniocerebral trauma. However, collecting intestinal stool and small intestinal tissues for broad target metabolomics, 16s rRNA bacteriomics, and the combined analysis of intestinal tissue proteomics revealed that oral administration of brain protein combined with probiotics activates glycerophospholipid and vitamin B6 metabolic pathways to promote the production of CD4⁺CD25⁺Foxp3⁺Treg. Therefore, we propose the novel idea that oral administration of brain protein combined with probiotics can induce immune tolerance by increasing Treg differentiation, thus, reducing secondary inflammatory injury following craniocerebral trauma.

Gram-negative multidrug-resistant organisms were dominant in neurorehabilitation ward patients in a general hospital in southwest China

This study aimed to investigate the prevalence of and risk factors for multidrug-resistant organism (MDRO) infection in the rehabilitation ward of a general hospital in Southwest China. We analyzed rehabilitation patients with nosocomial infections caused by MDROs from June 2016 to June 2020. MDRO infection pathogens and associated antibiotic resistance were calculated. Possible risk factors for MDRO-related infection in the neurorehabilitation ward were analyzed using chi-square, and logistic regression. A total of 112 strains of MDRO were found positive from 96 patients. The MDRO test-positive rate was 16.70% (96/575). Ninety-five MDRO strains were detected in sputum, of which 84.82% (95/112) were gram-negative bacteria. Acinetobacter baumannii (A. Baumannii), Pseudomonas aeruginosa (P. aeruginosa), and Klebsiella pneumonia (K. pneumonia) were the most frequently isolated MDRO strains. The logistic regression model and multifactorial analysis showed that long-term (≥ 7 days) antibiotic use (OR 6.901), history of tracheotomy (OR 4.458), and a low albumin level (< 40 g/L) (OR 2.749) were independent risk factors for the development of MDRO infection in patients in the rehabilitation ward (all P < 0.05). Gram-negative MRDOs were dominant in rehabilitation ward patients. Low albumin, history of a tracheostomy, and long-term use of antibiotics were independent risk factors for MRDO infection and are worthy of attention.

Heterologous COVID-19 Booster Vaccination in the Chronic Disorder of Consciousness: A Pilot Study

Significant anti-spike protein receptor-binding domain (S-RBD) antibody responses have been demonstrated in patients with chronic disorder of consciousness (DOC) completing a COVID-19 vaccine regime with BNT162b2 (Pfizer–BioNTech). We now provide further prospective data on the immunogenicity of these patients followed by heterologous booster injection with mRNA-1273 (Moderna). These patients were compared with two different demographically comparable healthcare workers (HCW) groups who underwent homologous booster injection with BNT162b2 vaccine or heterologous booster injection with mRNA-1273. Antibody responses were evaluated at 21 days after the administration of the booster dose of vaccination. Results: No severe adverse reactions were reported after each type of vaccination. Heterologous boosting with mRNA-1273 elicited a higher increase of S-RBD IgG levels than homologous boosting with BNT162b2 both in DOC patients and HCW who had previously received two doses of BNT162b2. No significant difference was detected between DOC and HCW patients who received heterologous boosting. Conclusions: Despite the small sample size, our preliminary results suggest that heterologous boosting with mRNA-1273, following initial vaccination with BNT162b2, is safe and tends to be more immunogenic than homologous boosting, either in fragile people or in healthy controls.

Fast Maturation of Splenic Dendritic Cells Upon TBI Is Associated With FLT3/FLT3L Signaling

The consequences of systemic inflammation are a significant burden after traumatic brain injury (TBI), with almost all organs affected. This response consists of inflammation and concurrent immunosuppression after injury. One of the main immune regulatory organs, the spleen, is highly interactive with the brain. Along this brain–spleen axis, both nerve fibers as well as brain-derived circulating mediators have been shown to interact directly with splenic immune cells. One of the most significant comorbidities in TBI is acute ethanol intoxication (EI), with almost 40% of patients showing a positive blood alcohol level (BAL) upon injury. EI by itself has been shown to reduce proinflammatory mediators dose-dependently and enhance anti-inflammatory mediators in the spleen. However, how the splenic immune modulatory effect reacts to EI in TBI remains unclear. Therefore, we investigated early splenic immune responses after TBI with and without EI, using gene expression screening of cytokines and chemokines and fluorescence staining of thin spleen sections to investigate cellular mechanisms in immune cells. We found a strong FLT3/FLT3L induction 3 h after TBI, which was enhanced by EI. The FLT3L induction resulted in phosphorylation of FLT3 in CD11c+ dendritic cells, which enhanced protein synthesis, maturation process, and the immunity of dendritic cells, shown by pS6, peIF2A, MHC-II, LAMP1, and CD68 by immunostaining and TNF-α expression by in-situ hybridization. In conclusion, these data indicate that TBI induces a fast maturation and immunity of dendritic cells which is associated with FLT3/FLT3L signaling and which is enhanced by EI prior to TBI.

Neuroinflammation Following Traumatic Brain Injury: Take It Seriously or Not

Traumatic brain injury (TBI) is associated with high mortality and disability, with a substantial socioeconomic burden. With the standardization of the treatment process, there is increasing interest in the role that the secondary insult of TBI plays in outcome heterogeneity. The secondary insult is neither detrimental nor beneficial in an absolute sense, among which the inflammatory response was a complex cascade of events and can thus be regarded as a double-edged sword. Therefore, clinicians should take the generation and balance of neuroinflammation following TBI seriously. In this review, we summarize the current human and animal model studies of neuroinflammation and provide a better understanding of the inflammatory response in the different stages of TBI. In particular, advances in neuroinflammation using proteomic and transcriptomic techniques have enabled us to identify a functional specific delineation of the immune cell in TBI patients. Based on recent advances in our understanding of immune cell activation, we present the difference between diffuse axonal injury and focal brain injury. In addition, we give a figurative profiling of the general paradigm in the pre- and post-injury inflammatory settings employing a bow-tie framework.

Sexual dimorphism in neurological function after SCI is associated with disrupted neuroinflammation in both injured spinal cord and brain

Whereas human spinal cord injury (SCI) is more common in men, the prevalence is growing in women. However, little is known about the effect of biological sex on brain dysfunction and injury mechanisms. To model the highest per capita rate of injury (ages between 16 and 30 years old) in humans, in the present study, young adult or a young/middle-aged male and female C57BL/6 mice were subjected to moderate contusion SCI. When mice were injured at 10-12-week-old, transcriptomic analysis of inflammation-related genes and flow cytometry revealed a more aggressive neuroinflammatory profile in male than females following 3 d SCI, ostensibly driven by sex-specific changes myeloid cell function rather than cell number. Female mice were generally more active at baseline, as evidenced by greater distance traveled in the open field. After SCI, female mice had more favorable locomotor function than male animals. At 13 weeks post-injury, male mice showed poor performance in cognitive and depressive-like behavioral tests, while injured female mice showed fewer deficits in these tasks. However, when injured at 6 months old followed by 8 months post-injury, male mice had considerably less inflammatory activation compared with female animals despite having similar or worse outcomes in affective, cognitive, and motor tasks. Collectively, these findings indicate that sex differences in functional outcome after SCI are associated with the age at onset of injury, as well as disrupted neuroinflammation not only at the site of injury but also in remote brain regions. Thus, biological sex should be considered when designing new therapeutic agents.

Mild-to-severe traumatic brain injury in children: altered cytokines reflect severity

Background

Paediatric traumatic brain injury (TBI) is recognised to have significant longer-term neurocognitive effects. Childhood is a time of high risk for head injury. Functional recovery is variable with a combination of any or all of physical, cognitive and emotional impairment. Immune activation and alteration in cytokine levels are present following TBI which may differ from adults.

Methods

Pro- and anti-inflammatory cytokines including Interleukin (IL)-2, IL-4, IL-6, IL-8, IL-10, IL-17A, Tumor Necrosis Factor (TNF)-α and Interferon (IFN)-γ were examined at baseline and following in vitro treatment with endotoxin of whole blood, in the following children: severe TBI (sTBI: initial Glasgow coma scale(GCS) ≤ 8), mild TBI (mTBI; GCS 14/15) at 0-4d and at 10-14d post-TBI and compared to healthy age-matched controls.

Results

The study enrolled 208 children, including 110 with TBI cohort (n = 104 mild; 6 severe) and controls (n = 98). At baseline all children with TBI had increased IL-6. The mTBI group had significantly increased IFN-γ versus controls. In sTBI at baseline, IFN-γ was decreased compared to controls. At baseline IL-8, IL-10, IL-17A, and TNF-α were decreased in mTBI compared to controls. This persisted at 2 week post-mTBI. The AUC for detecting mTBI was 0.801 CI (0.73–086) using IL6/IL10 ratio. mTBI showed a greater fold change in IL-8 and TNF-α in response to endotoxin stimulation, a response that persisted at 2 weeks. Children with sTBI did not have a significant IL-6 response to endotoxin, but did show an increase in IL-17A.

Conclusion

Children with all TBI including mTBI show altered cytokine profiles and altered endotoxin responses. Although cytokines increased in sTBI especially in response to endotoxin, suppressed responses were found in mTBI coupled with persistent immune dysfunction post-injury.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-022-02390-5.

Admission Lymphopenia Predicts Infectious Complications and Mortality in Traumatic Brain Injury Victims

BACKGROUND

Traumatic brain injury (TBI) is a major cause of mortality and disability associated with increased risk of secondary infections. Identifying a readily available biomarker may help direct TBI patient care. Herein, we evaluated whether admission lymphopenia could predict outcomes of TBI patients.

METHODS

This is a 10-year retrospective review of TBI patients with a head Abbreviated Injury Score 2 to 6 and absolute lymphocyte counts (ALC) collected within 24 h of admission. Exclusion criteria were death within 24 h of admission and presence of bowel perforation on admission. Demographics, admission data, injury severity score, mechanism of injury, and outcomes were collected. Association between baseline variables and outcomes was analyzed.

RESULTS

We included 2,570 patients; 946 (36.8%) presented an ALC ≤1,000 on admission (lymphopenic group). Lymphopenic patients were significantly older, less likely to smoke, and more likely to have heart failure, hypertension, or chronic kidney disease. Lymphopenia was associated with increased risks of mortality (OR = 1.903 [1.389-2.608]; P < 0.001) and pneumonia (OR = 1.510 [1.081-2.111]; P = 0.016), increased LOS (OR = 1.337 [1.217-1.469]; P < 0.001), and likelihood of requiring additional healthcare resources at discharge (OR = 1.669 [1.344-2.073], P < 0.001). Additionally, lymphopenia increased the risk of early in-hospital death (OR = 1.459 [1.097-1.941]; P = 0.009). Subgroup analysis showed that lymphopenia was associated with mortality in polytrauma patients and those who presented with two or more concurrent types of TBI. In all subgroup analyses, lymphopenia was associated with longer length of stay and discharge requiring higher level of care.

CONCLUSION

A routine complete blood count with differential for all TBI patients may help predict patient outcomes and direct care accordingly.

Admission Lymphopenia is Associated With Discharge Disposition in Blunt Chest Wall Trauma Patients

BACKGROUND

Lymphopenia contributes to the immune suppression observed in critical illness. However, its role in the immunologic response to trauma remains unclear. Herein, we assessed whether admission lymphopenia is associated with poor outcomes in patients with blunt chest wall trauma (BCWT).

METHODS

All adult patients with a Chest Abbreviated Injury Score (CAIS) ≥2 admitted to our Level I Trauma center between May 2009 and December 2018 were identified in our institution Trauma Registry. Patients with absolute lymphocyte counts (ALC) collected within 24 H of admission were included. Patients who died within 24 H of admission, had bowel perforation on admission, penetrating trauma, and burns were excluded. Demographics, injury characteristics, comorbidities, ALC, complications, and outcomes were collected. Lymphopenia was defined as an ALC ≤1000/µL. Association between lymphopenia and clinical outcomes of BCWT was assessed using multivariate analyses. P < 0.05 was considered significant.

RESULTS

A total of 1394 patients were included; 69.7% were male; 44.3% were lymphopenic. On univariate analysis, lymphopenia was associated with longer in-hospital stay (11.6±10.2 versus 10.1±11.4, P = 0.009), in-hospital death (9.7% versus 5.8%, P = 0.006), and discharge to a healthcare facility (60.9% versus 46.4%, P < 0.001). Controlling for Injury Severity Score, age, gender, and comorbidities, the association between lymphopenia and discharge to another facility (SNF/rehabilitation facility/ACH) (OR = 1.380 [1.041-1.830], P = 0.025) remained significant.

CONCLUSIONS

Lymphopenia on admission is associated with discharge requiring increased healthcare support. Routine lymphocyte count monitoring on admission may provide important prognostic information for BCWT patients.

Central nervous system injury-induced immune suppression

Central nervous system trauma is a common cause of morbidity and mortality. Additionally, these injuries frequently occur in younger individuals, leading to lifetime expenses for patients and caregivers and the loss of opportunity for society. Despite this prevalence and multiple attempts to design a neuroprotectant, clinical trials for a pharmacological agent for the treatment of traumatic brain injury (TBI) or spinal cord injury (SCI) have provided disappointing results. Improvements in outcome from these disease processes in the past decades have been largely due to improvements in supportive care. Among the many challenges facing patients and caregivers following neurotrauma, posttraumatic nosocomial infection is a significant and potentially reversible risk factor. Multiple animal and clinical studies have provided evidence of posttraumatic systemic immune suppression, and injuries involving the CNS may be even more prone, leading to a higher risk for in-hospital infections following neurotrauma. Patients who have experienced neurotrauma with nosocomial infection have poorer recovery and higher risks of long-term morbidity and in-hospital mortality than patients without infection. As such, the etiology and reversal of postneurotrauma immune suppression is an important topic. There are multiple possible etiologies for these posttraumatic changes including the release of damage-associated molecular patterns, the activation of immunosuppressive myeloid-derived suppressor cells, and sympathetic nervous system activation. Postinjury systemic immunosuppression, particularly following neurotrauma, provides a challenge for clinicians but also an opportunity for improvement in outcome. In this review, the authors sought to outline the evidence of postinjury systemic immune suppression in both animal models and clinical research of TBI, TBI polytrauma, and SCI.

Ageing is associated with maladaptive immune response and worse outcome after traumatic brain injury

Traumatic brain injury is increasingly common in older individuals. Older age is one of the strongest predictors for poor prognosis after brain trauma, a phenomenon driven by the presence of extra-cranial comorbidities as well as pre-existent pathologies associated with cognitive impairment and brain volume loss (such as cerebrovascular disease or age-related neurodegeneration). Furthermore, ageing is associated with a dysregulated immune response, which includes attenuated responses to infection and vaccination, and a failure to resolve inflammation leading to chronic inflammatory states. In traumatic brain injury, where the immune response is imperative for the clearance of cellular debris and survey of the injured milieu, an appropriate self-limiting response is vital to promote recovery. Currently, our understanding of age-related factors that contribute to the outcome is limited; but a more complete understanding is essential for the development of tailored therapeutic strategies to mitigate the consequences of traumatic brain injury. Here we show greater functional deficits, white matter abnormalities and worse long-term outcomes in aged compared with young C57BL/6J mice after either moderate or severe traumatic brain injury. These effects are associated with altered systemic, meningeal and brain tissue immune response. Importantly, the impaired acute systemic immune response in the mice was similar to the findings observed in our clinical cohort. Traumatic brain-injured patient cohort over 70 years of age showed lower monocyte and lymphocyte counts compared with those under 45 years. In mice, traumatic brain injury was associated with alterations in peripheral immune subsets, which differed in aged compared with adult mice. There was a significant increase in transcription of immune and inflammatory genes in the meninges post-traumatic brain injury, including monocyte/leucocyte-recruiting chemokines. Immune cells were recruited to the region of the dural injury, with a significantly higher number of CD11b⁺ myeloid cells in aged compared with the adult mice. In brain tissue, when compared with the young adult mice, we observed a more pronounced and widespread reactive astrogliosis 1 month after trauma in aged mice, sustained by an early and persistent induction of proinflammatory astrocytic state. These findings provide important insights regarding age-related exacerbation of neurological damage after brain trauma.

Anti-SARS-CoV-2 S-RBD IgG Antibody Responses after COVID-19 mRNA Vaccine in the Chronic Disorder of Consciousness: A Pilot Study

OBJECTIVE

In the last year, a large amount of research has investigated the anti-spike protein receptor-binding domain (S-RBD) antibody responses in patients at high risk of developing severe acute respiratory syndrome because of COVID-19 infection. However, no data are available on the chronic disorder of consciousness (DOC).

METHODS

Here, we evaluated anti-S-RBD IgG levels after vaccination in chronic DOC patients compared with demographically matched healthy controls (HC) by indirect chemiluminescence immunoassay. All individuals completed a two-dose-cycle vaccination with Pfizer mRNA vaccine (BNT162b2), and antibody responses were evaluated at 30 and 180 days after the administration of the second dose of vaccination.

RESULTS

We compared 32 DOC patients with 34 demographically matched healthy controls. Both DOC and HC groups showed a similar antibody response at 30 days, whereas at follow-up (180 days) DOC patients were characterized by lower S-RBD IgG levels with respect to controls. Additional multiple regression analyses including demographical and clinical comorbidities as predictors revealed that age was the only factor associated with the decrease in S-RBD IgG levels at follow-up (180 days). Elderly individuals of both groups were characterized by a reduction in the antibody responses with respect to younger individuals.

CONCLUSIONS

Our results show an efficacy seroconversion in DOC patients in the first period after vaccination, which significantly declines over time with respect to healthy controls.

Mice Born to Mothers with Gravida Traumatic Brain Injury Have Distorted Brain Circuitry and Altered Immune Responses

Intimate partner violence (IPV) increases risk of traumatic brain injury (TBI). Physical assaults increase in frequency and intensity during pregnancy. The consequences of TBI during pregnancy (gravida TBI; gTBI) on offspring development is unknown, for which stress and inflammation during pregnancy worsen fetal developmental outcomes. We hypothesized that gTBI would lead to increased anxiety- and depression-related behavior, altered inflammatory responses and gut pathology, and distorted brain circuitry in mixed-sex offspring compared to mice born to control mothers. Pregnant dams received either diffuse TBI or sham injury (control) 12 days post-coitum. We found that male gTBI offspring were principal drivers of the gTBI effects on health, physiology, and behavior. For example, male, but not female, gTBI offspring weighed significantly less at weaning compared to male control offspring. At post-natal day (PND) 28, gTBI offspring had significantly weaker intralaminar connectivity onto layer 5 pre-frontal pyramidal neurons compared to control offspring. Neurological performance on anxiety-like behaviors was decreased, with only marginal differences in depressive-like behaviors, for gTBI offspring compared to control offspring. At PND42 and PND58, circulating neutrophil and monocyte populations were significantly smaller in gTBI male offspring than control male offspring. In response to a subsequent inflammatory challenge at PND75, gTBI offspring had significantly smaller circulating neutrophil populations than control offspring. Anxiety-like behaviors persisted during the immune challenge in gTBI offspring. However, spleen immune response and gut histology showed no significant differences between groups. The results compel further studies to determine the full extent of gTBI on fetal and maternal outcomes.

Extracellular vesicles as distinct biomarker reservoirs for mild traumatic brain injury diagnosis

Mild traumatic brain injury does not currently have a clear molecular diagnostic panel to either confirm the injury or to guide its treatment. Current biomarkers for traumatic brain injury rely mainly on detecting circulating proteins in blood that are associated with degenerating neurons, which are less common in mild traumatic brain injury, or with broad inflammatory cascades which are produced in multiple tissues and are thus not brain specific. To address this issue, we conducted an observational cohort study designed to measure a protein panel in two compartments—plasma and brain-derived extracellular vesicles—with the following hypotheses: (i) each compartment provides independent diagnostic information and (ii) algorithmically combining these compartments accurately classifies clinical mild traumatic brain injury. We evaluated this hypothesis using plasma samples from mild (Glasgow coma scale scores 13–15) traumatic brain injury patients (n = 47) and healthy and orthopaedic control subjects (n = 46) to evaluate biomarkers in brain-derived extracellular vesicles and plasma. We used our Track Etched Magnetic Nanopore technology to isolate brain-derived extracellular vesicles from plasma based on their expression of GluR2, combined with the ultrasensitive digital enzyme-linked immunosorbent assay technique, Single-Molecule Array. We quantified extracellular vesicle-packaged and plasma levels of biomarkers associated with two categories of traumatic brain injury pathology: neurodegeneration and neuronal/glial damage (ubiquitin C-terminal hydrolase L1, glial fibrillary acid protein, neurofilament light and Tau) and inflammation (interleukin-6, interleukin-10 and tumour necrosis factor alpha). We found that GluR2+ extracellular vesicles have distinct biomarker distributions than those present in the plasma. As a proof of concept, we showed that using a panel of biomarkers comprised of both plasma and GluR2+ extracellular vesicles, injured patients could be accurately classified versus non-injured patients.

Systemic inflammation alters the neuroinflammatory response: a prospective clinical trial in traumatic brain injury

Background

Neuroinflammation following traumatic brain injury (TBI) has been shown to be associated with secondary injury development; however, how systemic inflammatory mediators affect this is not fully understood. The aim of this study was to see how systemic inflammation affects markers of neuroinflammation, if this inflammatory response had a temporal correlation between compartments and how different compartments differ in cytokine composition.

Methods

TBI patients recruited to a previous randomised controlled trial studying the effects of the drug anakinra (Kineret®), a human recombinant interleukin-1 receptor antagonist (rhIL1ra), were used (n = 10 treatment arm, n = 10 control arm). Cytokine concentrations were measured in arterial and jugular venous samples twice a day, as well as in microdialysis-extracted brain extracellular fluid (ECF) following pooling every 6 h. C-reactive protein level (CRP), white blood cell count (WBC), temperature and confirmed systemic clinical infection were used as systemic markers of inflammation. Principal component analyses, linear mixed-effect models, cross-correlations and multiple factor analyses were used.

Results

Jugular and arterial blood held similar cytokine information content, but brain-ECF was markedly different. No clear arterial to jugular gradient could be seen. No substantial delayed temporal associations between blood and brain compartments were detected. The development of a systemic clinical infection resulted in a significant decrease of IL1-ra, G-CSF, PDGF-ABBB, MIP-1b and RANTES (p < 0.05, respectively) in brain-ECF, even if adjusting for injury severity and demographic factors, while an increase in several cytokines could be seen in arterial blood.

Conclusions

Systemic inflammation, and infection in particular, alters cytokine levels with different patterns seen in brain and in blood. Cerebral inflammatory monitoring provides independent information from arterial and jugular samples, which both demonstrate similar information content. These findings could present potential new treatment options in severe TBI patients, but novel prospective trials are warranted to confirm these associations.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-021-02264-2.

Antimicrobial immunity impedes CNS vascular repair following brain injury

Traumatic brain injury (TBI) and cerebrovascular injury are leading causes of disability and mortality worldwide. Systemic infections often accompany these disorders and can worsen outcomes. Recovery after brain injury depends on innate immunity, but the effect of infections on this process is not well understood. Here, we demonstrate that systemically introduced microorganisms and microbial products interfered with meningeal vascular repair after TBI in a type I interferon (IFN-I)-dependent manner, with sequential infections promoting chronic disrepair. Mechanistically, we discovered that MDA5-dependent detection of an arenavirus encountered after TBI disrupted pro-angiogenic myeloid cell programming via induction of IFN-I signaling. Systemic viral infection similarly blocked restorative angiogenesis in the brain parenchyma after intracranial hemorrhage, leading to chronic IFN-I signaling, blood-brain barrier leakage and a failure to restore cognitive-motor function. Our findings reveal a common immunological mechanism by which systemic infections deviate reparative programming after central nervous system injury and offer a new therapeutic target to improve recovery.

Severe Traumatic Injury Induces Phenotypic and Functional Changes of Neutrophils and Monocytes

Background: Severe traumatic injury has been associated with high susceptibility for the development of secondary complications caused by dysbalanced immune response. As the first line of the cellular immune response, neutrophils and monocytes recruited to the site of tissue damage and/or infection, are divided into three different subsets according to their CD16/CD62L and CD16/CD14 expression, respectively. Their differential functions have not yet been clearly understood. Thus, we evaluated the phenotypic changes of neutrophil and monocyte subsets among their functionality regarding oxidative burst and the phagocytic capacity in severely traumatized patients. Methods: Peripheral blood was withdrawn from severely injured trauma patients (TP; n = 15, ISS ≥ 16) within the first 12 h post-trauma and from healthy volunteers (HV; n = 15) and stimulated with fMLP and PMA. CD16^dimCD62L^bright (immature), CD16^brightCD62L^bright (mature) and CD16^brightCD62L^dim (CD62L^low) neutrophil subsets and CD14^brightCD16⁻ (classical), CD14^brightCD16⁺ (intermediate) and CD14^dimCD16⁺ (non-classical) monocyte subsets of HV and TP were either directly analyzed by flow cytometry or the examined subsets of HV were sorted first by fluorescence-activated cell sorting and subsequently analyzed. Subset-specific generation of reactive oxygen species (ROS) and of E. coli bioparticle phagocytosis were evaluated. Results: In TP, the counts of immature neutrophils were significantly increased vs. HV. The numbers of mature and CD62L^dim neutrophils remained unchanged but the production of ROS was significantly enhanced in TP vs. HV and the stimulation with fMLP significantly increased the generation of ROS in the mature and CD62L^dim neutrophils of HV. The counts of phagocyting neutrophils did not change but the mean phagocytic capacity showed an increasing trend in TP. In TP, the monocytes shifted toward the intermediate phenotype, whereas the classical and non-classical monocytes became less abundant. ROS generation was significantly increased in all monocyte subsets in TP vs. HV and PMA stimulation significantly increased those level in both, HV and TP. However, the PMA-induced mean ROS generation was significantly lower in intermediate monocytes of TP vs. HV. Sorting of monocyte and neutrophil subsets revealed a significant increase of ROS and decrease of phagocytic capacity vs. whole blood analysis. Conclusions: Neutrophils and monocytes display a phenotypic shift following severe injury. The increased functional abnormalities of certain subsets may contribute to the dysbalanced immune response and attenuate the antimicrobial function and thus, may represent a potential therapeutic target. Further studies on isolated subsets are necessary for evaluation of their physiological role after severe traumatic injury.

Beneficial Effect of Immune-Enhanced Enteral Nutrition on Immune Function in Patients With Severe Neurological Diseases: A Single-Center Randomized Controlled Trial

Background: Undernutrition is the main reason for the use of artificial nutrition in patients with severe neurological diseases. However, the clinical and immunological outcomes of enteral nutrition supplemented with immunomodulatory nutrients in these patients remain unclear.

Methods: In this single-center, randomized controlled study, 57 patients with severe neurological diseases were randomly divided into the following two groups according to the type of enteral nutrition they would receive: immune-enhancing (IE) (n = 27) and non-IE (NIE) (n = 30). The IE and NIE groups received enteral nutrition supplemented with immunomodulatory nutrients and standard enteral nutrition, respectively. We compared the nutritional status and the state of cellular immunity between the patients of the two groups. Clinical and immunological variables were evaluated following nutritional treatment.

Results: Feeding intolerance was lower in the IE than that in the NIE group (P = 0.04). However, there were no significant differences between the results of the two groups in terms of length of stay in the intensive care unit or hospital, extubation time, or body mass index (P > 0.05). The CD4+ T-lymphocyte count and CD4⁺/CD8+ ratio in the peripheral blood increased significantly in the IE group. The expression of CD28 activated cell surface markers was higher in the IE than in the NIE group. In addition, increased plasma interferon-γ levels were recorded in the IE group, whereas the levels of tumor necrosis factor-α (TNF-α), interleukin (IL)-6, IL-8, and IL-10 decreased.

Conclusions: Immune-enhanced enteral nutrition could improve the immune status and feeding tolerance in patients with severe neurological diseases.

Trial Registration:www.chictr.org.cn/index.aspx, identifier: ChiCTR-IPR-17013909.

The Peripheral Immune System and Traumatic Brain Injury: Insight into the role of T-helper cells

Emerging evidence suggests that immune-inflammatory processes are key elements in the physiopathological events associated with traumatic brain injury (TBI). TBI is followed by T-cell-specific immunological changes involving several subsets of T-helper cells and the cytokines they produce; these processes can have opposite effects depending on the disease course and cytokine concentrations. Efforts are underway to identify the T-helper cells and cytokine profiles associated with prognosis. These predictors may eventually serve as effective treatment targets to decrease morbidity and mortality and to improve the management of TBI patients. Here, we review the immunological response to TBI, the possible molecular mechanisms of this response, and therapeutic strategies to address it.

RIPK1 or RIPK3 deletion prevents progressive neuronal cell death and improves memory function after traumatic brain injury

Traumatic brain injury (TBI) causes acute and subacute tissue damage, but is also associated with chronic inflammation and progressive loss of brain tissue months and years after the initial event. The trigger and the subsequent molecular mechanisms causing chronic brain injury after TBI are not well understood. The aim of the current study was therefore to investigate the hypothesis that necroptosis, a form a programmed cell death mediated by the interaction of Receptor Interacting Protein Kinases (RIPK) 1 and 3, is involved in this process. Neuron-specific RIPK1- or RIPK3-deficient mice and their wild-type littermates were subjected to experimental TBI by controlled cortical impact. Posttraumatic brain damage and functional outcome were assessed longitudinally by repetitive magnetic resonance imaging (MRI) and behavioral tests (beam walk, Barnes maze, and tail suspension), respectively, for up to three months after injury. Thereafter, brains were investigated by immunohistochemistry for the necroptotic marker phosphorylated mixed lineage kinase like protein(pMLKL) and activation of astrocytes and microglia. WT mice showed progressive chronic brain damage in cortex and hippocampus and increased levels of pMLKL after TBI. Chronic brain damage occurred almost exclusively in areas with iron deposits and was significantly reduced in RIPK1- or RIPK3-deficient mice by up to 80%. Neuroprotection was accompanied by a reduction of astrocyte and microglia activation and improved memory function. The data of the current study suggest that progressive chronic brain damage and cognitive decline after TBI depend on the expression of RIPK1/3 in neurons. Hence, inhibition of necroptosis signaling may represent a novel therapeutic target for the prevention of chronic post-traumatic brain damage.

The Role of T Cell Senescence in Neurological Diseases and Its Regulation by Cellular Metabolism

Immunosenescence is a state of dysregulated leukocyte function characterised by arrested cell cycle, telomere shortening, expression of markers of cellular stress, and secretion of pro-inflammatory mediators. Immunosenescence principally develops during aging, but it may also be induced in other pathological settings, such as chronic viral infections and autoimmune diseases. Appearance of senescent immune cells has been shown to potentially cause chronic inflammation and tissue damage, suggesting an important role for this process in organismal homeostasis. In particular, the presence of senescent T lymphocytes has been reported in neurological diseases, with some works pointing towards a direct connection between T cell senescence, inflammation and neuronal damage. In this minireview, we provide an overview on the role of T cell senescence in neurological disorders, in particular in multiple sclerosis and Alzheimer disease. We also discuss recent literature investigating how metabolic remodelling controls the development of a senescence phenotype in T cells. Targeting metabolic pathways involved in the induction of senescent T cells may indeed represent a novel approach to limit their inflammatory activity and prevent neuroinflammation and neurodegeneration.

Brain-gut axis dysfunction in the pathogenesis of traumatic brain injury

Traumatic brain injury (TBI) is a chronic and progressive disease, and management requires an understanding of both the primary neurological injury and the secondary sequelae that affect peripheral organs, including the gastrointestinal (GI) tract. The brain-gut axis is composed of bidirectional pathways through which TBI-induced neuroinflammation and neurodegeneration impact gut function. The resulting TBI-induced dysautonomia and systemic inflammation contribute to the secondary GI events, including dysmotility and increased mucosal permeability. These effects shape, and are shaped by, changes in microbiota composition and activation of resident and recruited immune cells. Microbial products and immune cell mediators in turn modulate brain-gut activity. Importantly, secondary enteric inflammatory challenges prolong systemic inflammation and worsen TBI-induced neuropathology and neurobehavioral deficits. The importance of brain-gut communication in maintaining GI homeostasis highlights it as a viable therapeutic target for TBI. Currently, treatments directed toward dysautonomia, dysbiosis, and/or systemic inflammation offer the most promise.

Human-derived Treg and MSC combination therapy may augment immunosuppressive potency in vitro, but did not improve blood brain barrier integrity in an experimental rat traumatic brain injury model

Traumatic brain injury (TBI) causes both physical disruption of the blood brain barrier (BBB) and altered immune responses that can lead to significant secondary brain injury and chronic inflammation within the central nervous system (CNS). Cell therapies, including mesenchymal stromal cells (MSC), have been shown to restore BBB integrity and augment endogenous splenic regulatory T cells (Treg), a subset of CD4+ T cells that function to regulate immune responses and prevent autoimmunity. We have recently shown that infusion of human cord blood-derived Treg decreased neuroinflammation after TBI in vivo and in vitro. However, while both cells have demonstrated anti-inflammatory and regenerative potential, they likely utilize differing, although potentially overlapping, mechanisms. Furthermore, studies investigating these two cell types together, as a combination therapy, are lacking. In this study, we compared the ability of Treg+MSC combination therapy, as well as MSC and Treg monotherapies, to improve BBB permeability in vivo and suppress inflammation in vitro. While Treg+MSC combination did not significantly augment potency in vivo, our in vitro data demonstrates that combination therapy may augment therapeutic potency and immunosuppressive potential compared to Treg or MSC monotherapy.

Combination of Neutrophil-to-Lymphocyte Ratio and Admission Glasgow Coma Scale Score Is Independent Predictor of Clinical Outcome in Diffuse Axonal Injury

BACKGROUND

The neutrophil-to-lymphocyte ratio (NLR) is an independent predictor of clinical outcome of different diseases, such as acute ischemic stroke, intracerebral hemorrhage, malignant tumor, and traumatic brain injury. However, the prognostic value of NLR plus admission Glasgow Coma Scale score (NLR-GCS) is still unclear in patients with diffuse axonal injury (DAI). Therefore this study assessed the relationship between the NLR-GCS and 6-month outcome of DAI patients.

METHODS

The clinical characteristics of DAI patients admitted to our department between January 2014 and January 2020 were retrospectively analyzed. The candidate risk factors were screened by using univariate analysis, and the independence of resultant risk factors was evaluated by the binary logistic regression analysis and least absolute shrinkage and selection operator regression analysis. The predictive value of NLR-GCS in an unfavorable outcome was assessed by the receiver operating characteristics curve analysis.

RESULTS

A total of 93 DAI patients were included. Binary logistic regression analysis and least absolute shrinkage and selection operator regression analysis showed the level of NLR on admission was an independent risk factor of unfavorable outcomes in DAI patients. The ROC curve analysis showed that the predictive capacity of the combination of NLR and admission GCS score and combination of NLR and coma duration outperformed NLR, admission GCS score, and coma duration alone.

CONCLUSIONS

The higher NLR level on admission is independently associated with unfavorable outcomes of DAI patients at 6 months. Furthermore, the combination of NLR and admission GCS score provides the superior predictive capacity to either NLR or GCS alone.

Inflammation in Traumatic Brain Injury

There is an increasing evidence that inflammation contributes to clinical and functional outcomes in traumatic brain injury (TBI). Many successful target-engaging, lesion-reducing, symptom-alleviating, and function-improving interventions in animal models of TBI have failed to show efficacy in clinical trials. Timing and immunological context are paramount for the direction, quality, and intensity of immune responses to TBI and the resulting neuroanatomical, clinical, and functional course. We present components of the immune system implicated in TBI, potential immune targets, and target-engaging interventions. The main objective of our article is to point toward modifiable molecular and cellular mechanisms that may modify the outcomes in TBI, and contribute to increasing the translational value of interventions that have been identified in animal models of TBI.

Alterations of Phagocytic Activity and Capacity in Granulocytes and Monocytes Depend on the Pathogen Strain in Porcine Polytrauma

Background: Polytraumatized patients undergo a strong immunological stress upon insult. Phagocytes (granulocytes and monocytes) play a substantial role in immunological defense against bacteria, fungi and yeast, and in the clearance of cellular debris after tissue injury. We have reported a reduced monocytes phagocytic activity early after porcine polytrauma before. However, it is unknown if both phagocyte types undergo those functional alterations, and if there is a pathogen-specific phagocytic behavior. We characterized the phagocytic activity and capacity of granulocytes and monocytes after polytrauma.

Methods: Eight pigs (Sus scrofa) underwent polytrauma consisting of lung contusion, liver laceration, tibial fracture and hemorrhagic shock with fluid resuscitation and fracture fixation with external fixator. Intensive care treatment including mechanical ventilation for 72 h followed. Phagocytic activity and capacity were investigated using an in vitro ex vivo whole blood stimulation phagocytosis assays before trauma, after surgery, 24, 48, and 72 h after trauma. Blood samples were stimulated with Phorbol-12-myristate-13-acetate and incubated with FITC-labeled E. coli, S. aureus or S. cerevisiae for phagocytosis assessment by flow cytometry.

Results: Early polytrauma-induced significant increase of granulocytes and monocytes declined to baseline values within 24 h. Percentage of E. coli-phagocytizing granulocytes significantly decreased after polytrauma and during further intensive care treatment, while their capacity significantly increased. Interestingly, both granulocytic phagocytic activity and capacity of S. aureus significantly decreased after trauma, although a recovery was observed after 24 h and yet was followed by another decrease. The percentage of S. cerevisiae-phagocytizing granulocytes significantly increased after 24 h, while their impaired capacity after surgery and 72 h later was detected. Monocytic E. coli-phagocytizing percentage did not change, while their capacity increased after 24–72 h. After a significant decrease in S. aureus-phagocytizing monocytes after surgery, a significant increase after 24 and 48 h was observed without capacity alterations. No significant changes in S. cerevisiae-phagocytizing monocytes occurred, but their capacity dropped 48 and 72 h.

Conclusion: Phagocytic activity and capacity of granulocytes and monocytes follow a different pattern and significantly change within 72 h after polytrauma. Both phagocytic activity and capacity show significantly different alterations depending on the pathogen strain, thus potentially indicating at certain and possibly more relevant infection causes after polytrauma.

Gene Expression Signature of Traumatic Brain Injury

Background: Traumatic brain injury (TBI) is a brain function change caused by external forces, which is one of the main causes of death and disability worldwide. The aim of this study was to identify early diagnostic markers and potential therapeutic targets for TBI.

Methods: Differences between TBI and controls in GSE89866 and GSE104687 were analyzed. The two groups of differentially expressed genes (DEGs) were combined for coexpression analysis, and the modules of interest were performed using enrichment analysis. Hub genes were identified by calculating area under curve (AUC) values of module genes, PPI network analysis, and functional similarity. Finally, the difference in immune cell infiltration between TBI and control was calculated by ssGSEA.

Results: A total of 4,817 DEGs were identified in GSE89866 and 1,329 DEGs in GSE104687. They were clustered into nine modules. The genes of modules 1, 4, and 7 had the most crosstalk and were identified as important modules. Enrichment analysis revealed that they were mainly associated with neurodevelopment and immune inflammation. In the PPI network constructed by genes with top 50 AUC values in module genes, we identified the top 10 genes with the greatest connectivity. Among them, down-regulated RPL27, RPS4X, RPL23A, RPS15A, and RPL7A had similar functions and were identified as hub genes. In addition, DC and Tem were significantly up-regulated and down-regulated between TBI and control, respectively.

Conclusion: We found that hub genes may have a diagnostic role for TBI. Molecular dysregulation mechanisms of TBI are associated with neurological and immune inflammation. These results may provide new ideas for the diagnosis and treatment of TBI.