Ischemic stroke is a major cause of death. Besides the direct damage resulting from oxygen and glucose deprivation, sterile inflammation plays a pivotal role in increasing cellular death. Damaged-associated molecular patterns (DAMPs) are passively released from dying cells and activate the innate immune system. Thus, they take part in the direct and rapid activation of the inflammatory response after stroke onset. In this review the role of the most important DAMPs, high mobility group box 1, heat and cold shock proteins, purines, and peroxiredoxins, are addressed. Moreover, intracellular pathways activated by DAMPs in microglia are illuminated.

The P2X7 channel is involved in the pathogenesis of various CNS diseases. An increasing number of studies suggest its presence in neurons where its putative functions remain controversial for more than a decade. To resolve this issue and to provide a model for analysis of P2X7 functions, we generated P2X7 BAC transgenic mice that allow visualization of functional EGFP-tagged P2X7 receptors in vivo. Extensive characterization of these mice revealed dominant P2X7-EGFP protein expression in microglia, Bergmann glia, and oligodendrocytes, but not in neurons. These findings were further validated by microglia- and oligodendrocyte-specific P2X7 deletion and a novel P2X7-specific nanobody. In addition to the first quantitative analysis of P2X7 protein expression in the CNS, we show potential consequences of its overexpression in ischemic retina and post-traumatic cerebral cortex grey matter. This novel mouse model overcomes previous limitations in P2X7 research and will help to determine its physiological roles and contribution to diseases.

Immune cells at sites of inflammation are continuously activated by local antigens and cytokines, and regulatory mechanisms must be enacted to control inflammation. The stepwise hydrolysis of extracellular ATP by ectonucleotidases CD39 and CD73 generates adenosine, a potent immune suppressor. Here we report that human effector CD8 T cells contribute to adenosine production by releasing CD73-containing extracellular vesicles upon activation. These extracellular vesicles have AMPase activity, and the resulting adenosine mediates immune suppression independently of regulatory T cells. In addition, we show that extracellular vesicles isolated from the synovial fluid of patients with juvenile idiopathic arthritis contribute to T cell suppression in a CD73-dependent manner. Our results suggest that the generation of adenosine upon T cell activation is an intrinsic mechanism of human effector T cells that complements regulatory T cell-mediated suppression in the inflamed tissue. Finally, our data underscore the role of immune cell-derived extracellular vesicles in the control of immune responses.

When a main artery of the brain occludes, a cellular response involving multiple cell types follows. Cells directly affected by the lack of glucose and oxygen in the neuronal core die by necrosis. In the periphery surrounding the ischemic core (the so-called penumbra) neurons, astrocytes, microglia, oligodendrocytes, pericytes, and endothelial cells react to detrimental factors such as excitotoxicity, oxidative stress, and inflammation in different ways. The fate of the neurons in this area is multifactorial, and communication between all the players is important for survival. This review focuses on the latest research relating to synaptic loss and the release of apoptotic bodies and other extracellular vesicles for cellular communication in stroke. We also point out possible treatment options related to increasing neuronal survival and regeneration in the penumbra.

The aim of this study was to describe the neurological syndrome in the largest cohort of adult patients with a complicated Shiga toxin-producing Escherichia coli infection. The recent outbreak of Shiga toxin-producing E. coli serotype O104:H4 in northern Germany affected more than 3842 patients, 22% of whom developed haemolytic uraemic syndrome. The proportion of adult patients was unusually high, and neurological complications were frequent and severe. In three hospitals, population-based evaluation of 217 patients with complicated Shiga toxin-producing E. coli infection was carried out, including neurological, neuroradiological, neurophysiological, cerebrospinal fluid and neuropathological analyses. Of the 217 patients with complicated Shiga toxin-producing E. coli infection, 104 (48%) developed neurological symptoms. Neurological symptoms occurred 5.3 days (mean) after first diarrhoea and 4 days after onset of haemolytic uraemic syndrome. Of the infected patients with neurological symptoms, 67.3% presented with cognitive impairment or aphasia. During the course of the disease, 20% of the patients developed epileptic seizures. The onset of neurological symptoms was paralleled by increases in blood urea nitrogen and serum creatinine. In 70 patients with cerebral magnetic resonance imaging, the most common findings were symmetrical hyperintensities in the region of abducens nucleus and lateral thalamus. On follow-up scans, these abnormalities were resolved. Neuropathological analysis revealed regionally accentuated astrogliosis and microgliosis, more predominant in the thalamus and brainstem than in the cortex, and neuronal expression of globotriaosylceramide. There were no signs of microbleeds, thrombotic vessel occlusion or ischaemic infarction. The neurological syndrome in adult patients with complicated Shiga toxin-producing E. coli infection is a rapidly progressive and potentially life-threatening disease necessitating intensive care unit treatment and intubation in >30% of cases. The outcome of neurological patients in the 2011 northern German Shiga toxin-producing E. coli O104:H4 outbreak was surprisingly good. Magnetic resonance imaging and neuropathological findings point to a mixed toxic and inflammatory pathomechanism leading to largely reversible damage of neuronal function.

Background and Purpose—: Inflammatory mechanisms can exacerbate ischemic tissue damage and worsen clinical outcome in patients with stroke. Both αβ and γδ T cells are established mediators of tissue damage in stroke, and the role of dendritic cells (DCs) in inducing the early events of T cell activation and differentiation in stroke is not well understood. Methods—: In a murine model of experimental stroke, we defined the immune phenotype of infiltrating DC subsets based on flow cytometry of surface markers, the expression of ontogenetic markers, and cytokine levels. We used conditional DC depletion, bone marrow chimeric mice, and IL-23 (interleukin-23) receptor-deficient mice to further explore the functional role of DCs. Results—: We show that the ischemic brain was rapidly infiltrated by IRF4 ⁺ /CD172a ⁺ conventional type 2 DCs and that conventional type 2 DCs were the most abundant subset in comparison with all other DC subsets. Twenty-four hours after ischemia onset, conventional type 2 DCs became the major source of IL-23, promoting neutrophil infiltration by induction of IL-17 (interleukin-17) in γδ T cells. Functionally, the depletion of CD11c ⁺ cells or the genetic disruption of the IL-23 signaling abrogated both IL-17 production in γδ T cells and neutrophil infiltration. Interruption of the IL-23/IL-17 cascade decreased infarct size and improved neurological outcome after stroke. Conclusions—: Our results suggest a central role for interferon regulatory factor 4-positive IL-23–producing conventional DCs in the IL-17–dependent secondary tissue damage in stroke.