PMC:6354430 / 2278-7622 JSONTXT

{"project":"2_test","denotations":[{"id":"30704498-22640592-63046365","span":{"begin":157,"end":158},"obj":"22640592"},{"id":"30704498-15297965-63046366","span":{"begin":593,"end":594},"obj":"15297965"},{"id":"30704498-27352145-63046367","span":{"begin":967,"end":968},"obj":"27352145"},{"id":"30704498-15931302-63046367","span":{"begin":967,"end":968},"obj":"15931302"},{"id":"30704498-25802426-63046367","span":{"begin":967,"end":968},"obj":"25802426"},{"id":"30704498-27337340-63046368","span":{"begin":1106,"end":1107},"obj":"27337340"},{"id":"30704498-20966214-63046369","span":{"begin":1340,"end":1341},"obj":"20966214"},{"id":"30704498-15831717-63046370","span":{"begin":1438,"end":1440},"obj":"15831717"},{"id":"30704498-22632727-63046371","span":{"begin":1442,"end":1444},"obj":"22632727"},{"id":"30704498-16541438-63046372","span":{"begin":1618,"end":1620},"obj":"16541438"},{"id":"30704498-22302798-63046373","span":{"begin":1662,"end":1664},"obj":"22302798"},{"id":"30704498-18208541-63046374","span":{"begin":1666,"end":1668},"obj":"18208541"},{"id":"30704498-19945511-63046375","span":{"begin":1725,"end":1727},"obj":"19945511"},{"id":"30704498-21943001-63046376","span":{"begin":1729,"end":1731},"obj":"21943001"},{"id":"30704498-18374991-63046377","span":{"begin":1759,"end":1761},"obj":"18374991"},{"id":"30704498-25165111-63046378","span":{"begin":1763,"end":1765},"obj":"25165111"},{"id":"30704498-26667390-63046379","span":{"begin":1950,"end":1952},"obj":"26667390"},{"id":"30704498-16103196-63046379","span":{"begin":1950,"end":1952},"obj":"16103196"},{"id":"30704498-8645088-63046380","span":{"begin":2296,"end":2298},"obj":"8645088"},{"id":"30704498-17909632-63046381","span":{"begin":2382,"end":2384},"obj":"17909632"},{"id":"30704498-15558055-63046382","span":{"begin":2386,"end":2388},"obj":"15558055"},{"id":"30704498-23111065-63046383","span":{"begin":2495,"end":2497},"obj":"23111065"},{"id":"30704498-17035323-63046384","span":{"begin":2711,"end":2713},"obj":"17035323"},{"id":"30704498-7835918-63046385","span":{"begin":2845,"end":2847},"obj":"7835918"},{"id":"30704498-1722099-63046385","span":{"begin":2845,"end":2847},"obj":"1722099"},{"id":"30704498-2543751-63046385","span":{"begin":2845,"end":2847},"obj":"2543751"},{"id":"30704498-15254203-63046385","span":{"begin":2845,"end":2847},"obj":"15254203"},{"id":"30704498-15254203-63046386","span":{"begin":3076,"end":3078},"obj":"15254203"},{"id":"30704498-20966214-63046387","span":{"begin":3280,"end":3281},"obj":"20966214"},{"id":"30704498-27083478-63046388","span":{"begin":3526,"end":3528},"obj":"27083478"},{"id":"30704498-22542597-63046389","span":{"begin":3530,"end":3532},"obj":"22542597"},{"id":"30704498-22729249-63046390","span":{"begin":3640,"end":3642},"obj":"22729249"},{"id":"30704498-22729249-63046391","span":{"begin":3805,"end":3807},"obj":"22729249"},{"id":"30704498-27516055-63046392","span":{"begin":4048,"end":4050},"obj":"27516055"},{"id":"30704498-29235509-63046393","span":{"begin":4245,"end":4247},"obj":"29235509"},{"id":"30704498-28251674-63046394","span":{"begin":4249,"end":4251},"obj":"28251674"},{"id":"30704498-29803827-63046395","span":{"begin":4297,"end":4299},"obj":"29803827"},{"id":"30704498-26232154-63046396","span":{"begin":4327,"end":4329},"obj":"26232154"}],"text":"Background\nWest Nile virus (WNV) is an emerging human pathogen that causes seasonal outbreaks through the Western hemisphere since its introduction in 1999 [1]. A member of the Flavivirus genus, WNV is an enveloped, single-stranded positive sense RNA virus that cycles between birds and mosquitos. Symptoms of WNV infection can range from a relatively mild flu-like illness, West Nile fever, to severe neuroinvasive disease. After peripheral infection, WNV replicates within lymphoid tissues before entering the CNS, where it targets neurons in the cerebellum, brainstem, and cerebral cortex [2, 3]. In 2017, 2002 symptomatic WNV cases were reported to the CDC, and of those, 1339 (67%) were classified as neuroinvasive [4]. Prolonged neurological deficits, which include motor functions, verbal learning and memory, and executive functions, are a significant problem for survivors of WNV infection and appear to manifest even in cases where neuroinvasion is absent [5–7]. Recent work indicates that persistent phagocytic microglia contribute to prolonged cognitive dysfunction following WNV encephalitis [8], and thus, limiting microglial activation may alleviate the associated neurological sequelae.\nMicroglia are the resident immune cells in the CNS, originating from yolk sac progenitor cells that seed the brain early in development [9]. In addition to a multitude of homeostatic functions throughout development and healthy aging [10, 11], microglia participate in both innate and adaptive immune responses through recognition of pathogen-associated molecular patterns and damage-associated molecular patterns [12], which stimulate morphological changes [13, 14] and increase production of reactive oxidative species [15, 16] and cytokines/chemokines [17, 18]. During neurotropic virus infection, virally infected cells secrete chemokines including CCL2, CCL5, and CXCL10, which facilitate immune cells crossing the blood brain barrier (BBB) [19–21]. Mononuclear cell infiltration into the CNS is a hallmark of WNV encephalitis, and monocytes and T cells are critical for CNS virologic control. Elimination of monocytes using a liposome-encapsulated drug dichloromethylene diphosphonate or by genetic deletion of CCR2 increases mortality in mice infected with a neurotropic strain of WNV [22, 23]. However, monocytes may also contribute to dissemination of virus to the CNS [24, 25], and inhibition of monocyte infiltration may also protect against nitric oxide-mediated immunopathology [26]. CD4+ T cells produce antiviral molecules, such as interferon γ (IFNγ) and IL-2, which promotes antiviral humoral immunity and sustains WNV-specific CD8+ T cell responses, enabling viral clearance in all organs [27, 28]. CD8+ T cells contribute to viral clearance and recovery from WNV infection via both cytopathic and noncytopathic mechanisms [29–32]. Mice lacking either CD8+ T cells or MHC-I molecules have higher CNS viral burdens, increased mortality after infection, and prolonged viral persistence, suggesting that cell-mediated immunity controls virus within the CNS [32].\nCSF1 receptor (CSF1R) signaling is essential for the development of many mononuclear phagocytes including microglia. Tissue-resident macrophages, such as microglia, fail to develop in Csf1r−/− mice [9], but in contrast to many tissue macrophages, adult microglia can still form in Csf1op/op mice, which carry a natural null mutation in the Csf1 gene [33]. This is due to an alternative CSF1R ligand, IL-34, which is highly expressed by neurons [34, 35]. Similar to Csf1op/op mice, IL-34−/− mice develop fewer microglia but do not lack peripheral macrophages [36]. These mice are more susceptible to lethal neurotropic WNV infection, which is associated with increased neuronal apoptosis without increased viral replication [36]. In order to temporally control microglial depletion, pharmacologic agents that antagonize CSF1R have been developed, including antagonist PLX5622, which depletes microglia in as little as 3 days and may be sustained for at least 6 weeks [37]. These agents are being investigated as therapeutics in models of neurodegenerative diseases in which microglial activation is considered a contributing factor, such as traumatic brain injury [38, 39], experimental autoimmune encephalomyelitis [40], and Alzheimer’s disease [41]. Here, we used PLX5622 in a model of WNV encephalitis to examine the effect of CSF1R antagonism in the setting of neurotropic viral infection. Our results show that mice treated with PLX5622 are more susceptible to lethal WNV infection, which is associated with increased CNS viral burden and neuronal apoptosis. PLX5622 also reduced expression of proinflammatory cytokines and B7 co-stimulatory molecules within the infected CNS by depleting cellular sources, including resident microglia and infiltrating macrophages, as well as decreasing expression on peripheral antigen-presenting cells (APCs). The loss of APCs in the CNS resulted in limited local reactivation of recruited antiviral CD8+ T cells, which are required for virologic control in the CNS. Together, these data demonstrate the impact of CSF1R antagonism on APC activation during viral infection in both the CNS and periphery and highlight the importance of microglia in orchestrating cell-mediated antiviral immunity during neurotropic infection."}