Activation of JAK/STAT3 restores NK-cell function and improves immune defense after brain ischemia.

Stroke-induced immune suppression predisposes the host to infections and can contribute to high morbidity and mortality in stroke patients. Because ischemic stroke has a profound effect on the systemic immune response, which may explain the increased susceptibility of stroke patients to infection, an urgent need persists for a better understanding of mechanisms associated with immune suppression; new and effective treatments for stroke can then be identified. NK cells play a key role in early host defense against pathogens by killing infected cells and/or producing cytokines such as IFN-γ. Because the phenotype and function of peripheral NK cells have been widely investigated in ischemic stroke, nCounter Inflammation Gene Array Analysis was used to build immune-related gene profiles of NK cells to comprehensively analyze the molecular signature of NK cells after ischemic brain injury. We observed distinct gene expression profiles reflecting different splenic NK-cell phenotypes and functional properties across the time course of transient middle cerebral artery occlusion (MCAO). Based on gene expression and pathway-network analysis, lower expression levels of signal transducer and activator of transcription-3 (STAT3) were observed in animals with MCAO compared with sham control animals. Genetic activation of STAT3 through the introduction of STAT3 clustered regularly interspaced short palindromic repeats (CRISPR) plasmid prevented the loss of NK-cell-derived IFN-γ production after MCAO, together with reduced bacterial burden and mortality. Our data suggest that brain ischemia impairs NK-cell-mediated immune defense in the periphery, at least in part through the JAK-STAT3 pathway, which can be readdressed by modulating STAT3 activation status.-Jin, W.-N., Ducruet, A. F., Liu, Q., Shi, S. X.-Y., Waters, M., Zou, M., Sheth, K. N., Gonzales, R., Shi, F.-D. Activation of JAK/STAT3 restores NK-cell function and improves immune defense after brain ischemia.

Depletion of microglia exacerbates postischemic inflammation and brain injury.

Brain ischemia elicits microglial activation and microglia survival depend on signaling through colony-stimulating factor 1 receptor (CSF1R). Although depletion of microglia has been linked to worse stroke outcomes, it remains unclear to what extent and by what mechanisms activated microglia influence ischemia-induced inflammation and injury in the brain. Using a mouse model of transient focal cerebral ischemia and reperfusion, we demonstrated that depletion of microglia via administration of the dual CSF1R/c-Kit inhibitor PLX3397 exacerbates neurodeficits and brain infarction. Depletion of microglia augmented the production of inflammatory mediators, leukocyte infiltration, and cell death during brain ischemia. Of note, microglial depletion-induced exacerbation of stroke severity did not solely depend on lymphocytes and monocytes. Importantly, depletion of microglia dramatically augmented the production of inflammatory mediators by astrocytes after brain ischemia . In vitro studies reveal that microglia restricted ischemia-induced astrocyte response and provided neuroprotective effects. Our findings suggest that neuroprotective effects of microglia may result, in part, from its inhibitory action on astrocyte response after ischemia.

Non-invasive tracking of CD4+ T cells with a paramagnetic and fluorescent nanoparticle in brain ischemia.

Recent studies have demonstrated that lymphocytes play a key role in ischemic brain injury. However, there is still a lack of viable approaches to non-invasively track infiltrating lymphocytes and reveal their key spatiotemporal events in the inflamed central nervous system (CNS). Here we describe an in vivo imaging approach for sequential monitoring of brain-infiltrating CD4(+) T cells in experimental ischemic stroke. We show that magnetic resonance imaging (MRI) or Xenogen imaging combined with labeling of SPIO-Molday ION Rhodamine-B (MIRB) can be used to monitor the dynamics of CD4(+) T cells in a passive transfer model. MIRB-labeled CD4(+) T cells can be longitudinally visualized in the mouse brain and peripheral organs such as the spleen and liver after cerebral ischemia. Immunostaining of tissue sections showed similar kinetics of MIRB-labeled CD4(+) T cells when compared with in vivo observations. Our results demonstrated the use of MIRB coupled with in vivo imaging as a valid method to track CD4(+) T cells in ischemic brain injury. This approach will facilitate future investigations to identify the dynamics and key spatiotemporal events for brain-infiltrating lymphocytes in CNS inflammatory diseases.

Interleukin-10 producing-B cells and their association with responsiveness to rituximab in myasthenia gravis.

INTRODUCTION: A subset of regulatory B cells in humans and mice has been defined functionally by their ability to produce interleukin (IL)-10. We characterized IL-10-producing B (B10) cells in myasthenia gravis (MG) patients and correlated them with disease activity and responsiveness to rituximab therapy. METHODS: Frequencies of B10 cells from MG patients and healthy controls were monitored by fluorescence-activated cell sorting (FACS). RESULTS: MG patients had fewer B10 cells than controls, which was associated with more severe disease status. Moreover, patients who responded well to rituximab therapy exhibited rapid repopulation of B10 cells, whereas in patients who did not respond well to rituximab, B10 cell repopulation was delayed. The kinetics of B10 cells were related to the responsiveness to rituximab in MG. CONCLUSIONS: We have characterized a specific subset of B10 cells in MG patients which may serve as a marker for disease activity and responsiveness to immune therapy.