The neuroimmune system is involved in development, normal functioning, aging, and injury of the central nervous system. Microglia, first described a century ago, are the main neuroimmune cells and have three essential functions: a sentinel function involved in constant sensing of changes in their environment, a housekeeping function that promotes neuronal well-being and normal operation, and a defense function necessary for responding to such changes and providing neuroprotection. Microglia use a defined armamentarium of genes to perform these tasks. In response to specific stimuli, or with neuroinflammation, microglia also have the capacity to damage and kill neurons. Injury to neurons in Alzheimer's, Parkinson's, Huntington's, and prion diseases, as well as in amyotrophic lateral sclerosis, frontotemporal dementia, and chronic traumatic encephalopathy, results from disruption of the sentinel or housekeeping functions and dysregulation of the defense function and neuroinflammation. Pathways associated with such injury include several sensing and housekeeping pathways, such as the Trem2, Cx3cr1 and progranulin pathways, which act as immune checkpoints to keep the microglial inflammatory response under control, and the scavenger receptor pathways, which promote clearance of injurious stimuli. Peripheral interference from systemic inflammation or the gut microbiome can also alter progression of such injury. Initiation or exacerbation of neurodegeneration results from an imbalance between these microglial functions; correcting such imbalance may be a potential mode for therapy.

SUMMARY Traumatic brain injury (TBI) is a leading cause of morbidity and disability, with a considerable socioeconomic burden. Heterogeneity of pathoanatomical subtypes and diversity in the pathogenesis and extent of injury contribute to differences in the course and outcome of TBI. Following the primary injury, extensive and lasting damage is sustained through a complex cascade of events referred to as “secondary injury”. Neuroinflammation is proposed as an important manipulable aspect of secondary injury in animal and human studies. Because neuroinflammation can be detrimental or beneficial, before developing immunomodulatory therapies, it is necessary to better understand the timing and complexity of the immune responses that follows TBI. With a rapidly increasing body of literature, there is a need for a clear summary of TBI neuroimmunology. This review presents our current understanding of the immune response to TBI in a chronological and compartment-based manner, highlighting early changes in gene expression and initial signaling pathways that lead to activation of innate and adaptive immunity. Based on recent advances in our understanding of innate immune cell activation, we propose a new paradigm to study innate immune cells following TBI that moves away from the existing M1/M2 classification of activation states towards a stimulus and disease-specific understanding of polarization state based on transcriptomic and proteomic profiling.

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In our msTBI cohort, WOC was the most important predictor of in-hospital mortality. We identified several important independent predictors of WOC. Large within-center variability in msTBI outcome prognostication with varying levels of possible clinical nihilism exists, which may form the basis of self-fulfilling prophecies.

ObjectiveTo test the hypothesis that racial-, age- and sex-specific incidence of cerebral venous thrombosis (CVT) has increased in the United States over the last decade.MethodsIn this retrospective cohort study, validated International Classification of Disease codes were used to identify all new cases of CVT (n = 5,567) in the State Inpatients Database (SID) of New York and Florida (2006–2016). A new CVT case was defined as first hospitalization for CVT in the SID without prior CVT hospitalization. CVT counts were combined with annual Census data to compute incidence. Joinpoint regression was used to evaluate trends in incidence over time.ResultsFrom 2006 to 2016, annual age and sex-standardized incidence of CVT in cases/million population ranged from 13.9 to 20.2, but incidence varied significantly by sex (females: 20.3–26.9; males 6.8–16.8) and by age/sex (females 18–44 yo: 24.0%–32.6%; males: 18–44 yo: 5.3–12.8). Incidence also differed by race (Blacks: 18.6–27.2; Whites: 14.3–18.5; Asians: 5.1–13.8). On joinpoint regression, incidence increased across 2006–2016 but most of this increase was driven by increase in all age groups of males (combined annualized percentage change [APC] 9.2%, p-value <0.001), females 45–64 yo (APC 7.8%, p-value <0.001) and females ≥65 yo (APC 7.4%, p-value <0.001). Incidence in females 18–44 yo remained unchanged over time.ConclusionCVT incidence is disproportionately higher in blacks compared to other races. New CVT hospitalizations increased significantly over the last decade mainly in males and older females. Further studies are needed to determine whether this increase represents true increase from changing risk factors or artefactual increase from improved detection.

Background: COVID-19 infection varies in severity from minimal symptoms to critical illness associated with a hyperinflammatory response. Data on disease progression in immunosuppressed solid organ transplant (SOT) recipients are limited. Methods: We examined the electronic medical records of all SOT recipients with COVID-19 from 12 Massachusetts hospitals between February 1, and May 6, 2020. We analyzed the demographics, clinical parameters, course, and outcomes of illness in these patients. Results: Of 52 COVID-19-positive SOT patients, 77% were hospitalized and 35% required ICU admission. Sixty-nine percent of hospitalized patients had immunosuppression reduced, 6% developed suspected rejection. Co-infections occurred in 45% in ICU vs 5% in non-ICU patients (P = .037). A biphasic pattern of evolution of laboratory tests was observed. In the first 5 days of illness, inflammatory markers were moderately increased. Subsequently, WBC, CRP, ferritin, and D Dimer increased with increasing stay in the ICU, and lymphocyte counts were similar. Five patients (16%) died. Conclusions: Our data indicate that SOT is associated with high rate of hospitalization, ICU admission, and death from COVID-19 compared to data in the general population of patients with COVID-19. Despite reduction in immunosuppression, suspected rejection was rare. The clinical course and trend of laboratory biomarkers is biphasic with a later, pronounced peak in inflammatory markers seen in those admitted to an ICU. CRP is a useful marker to monitor disease progression in SOT.

The neuroinflammatory response to traumatic brain injury (TBI) is critical to both neurotoxicity and neuroprotection, and has been proposed as a potentially modifiable driver of secondary injury in animal and human studies. Attempts to broadly target immune activation have been unsuccessful in improving outcomes, in part because the precise cellular and molecular mechanisms driving injury and outcome at acute, subacute, and chronic time points after TBI remain poorly defined. Microglia play a critical role in neuroinflammation and their persistent activation may contribute to long-term functional deficits. Activated microglia are characterized by morphological transformation and transcriptomic changes associated with specific inflammatory states. We analyzed the temporal course of changes in inflammatory genes of microglia isolated from injured brains at 2, 14, and 60 days after controlled cortical impact (CCI) in mice, a well-established model of focal cerebral contusion. We identified a time dependent, injury-associated change in the microglial gene expression profile toward a reduced ability to sense tissue damage, perform housekeeping, and maintain homeostasis in the early stages following CCI, with recovery and transition to a specialized inflammatory state over time. This later state starts at 14 days post-injury and is characterized by a biphasic pattern of IFNγ, IL-4, and IL-10 gene expression changes, with concurrent proinflammatory and anti-inflammatory gene changes. Our transcriptomic data sets are an important step to understand microglial role in TBI pathogenesis at the molecular level and identify common pathways that affect outcome. More studies to evaluate gene expression at the single cell level and focusing on subacute and chronic timepoint are warranted.

Background Recovery of functional independence is possible in patients with brainstem traumatic axonal injury (TAI), also referred to as “grade 3 diffuse axonal injury,” but acute prognostic biomarkers are lacking. We hypothesized that the extent of dorsal brainstem TAI measured by burden of traumatic microbleeds (TMBs) correlates with 1-year functional outcome more strongly than does ventral brainstem, corpus callosal, or global brain TMB burden. Further, we hypothesized that TMBs within brainstem nuclei of the ascending arousal network (AAN) correlate with 1-year outcome. Methods Using a prospective outcome database of patients treated for moderate-to-severe traumatic brain injury (TBI) at an inpatient rehabilitation hospital, we retrospectively identified 39 patients who underwent acute gradient-recalled echo (GRE) MRI. TMBs were counted on the acute GRE scans globally and in the dorsal brainstem, ventral brainstem, and corpus callosum. TMBs were also mapped onto an atlas of AAN nuclei. The primary outcome was the Disability Rating Scale (DRS) score at 1 year post-injury. Associations between regional TMBs, AAN TMB volume, and 1-year DRS score were assessed by calculating Spearman rank correlation coefficients. Results Mean+/−SD number of TMBs were: dorsal brainstem=0.7+/−1.4, ventral brainstem=0.2+/−0.6, corpus callosum=1.8+/−2.8, and global=14.4+/−12.5. The mean+/−SD TMB volume within AAN nuclei was 6.1+/−18.7 mm3. Increased dorsal brainstem TMBs and larger AAN TMB volume correlated with worse 1-year outcomes (R=0.37, p=0.02, and R=0.36, p=0.02, respectively). Global, callosal, and ventral brainstem TMBs did not correlate with outcomes. Conclusions These findings suggest that dorsal brainstem TAI, especially involving AAN nuclei, may have greater prognostic utility than the total number of lesions in the brain or brainstem.