IL-1R1 Signaling Regulates CXCL12-Mediated T Cell Localization and Fate within the Central Nervous System during West Nile Virus Encephalitis

Abstract

Immune cell entry into the virally infected central nervous system (CNS) is vital for promoting viral clearance yet may contribute to neuropathology if not rigorously regulated. We previously showed that signaling through the interleukin 1 receptor (IL-1R1) is critical for effector T cell reactivation and virologic control within the CNS during murine West Nile virus (WNV) encephalitis. WNV-infected IL-1R1−/− mice also display increased parenchymal penetration of CD8+ T cells despite lack of CD4-mediated full activation, suggesting dysregulation of molecular components of CNS immune privilege. Here, we show that IL-1 signaling regulates the CNS entry of virus-specific lymphocytes, promoting protective immune responses to CNS viral infections that limit immunopathology. Analysis of blood-brain barrier (BBB) function in the WNV-infected IL-1R1−/− mice revealed no alterations in permeability. However, parenchymal proinflammatory chemokine expression, including CCL2, CCL5 and CXCL10, was significantly upregulated, whereas microvasculature CXCL12 expression was significantly decreased in the absence of IL-1 signaling. We show that during WNV infection, CD11b+CD45hi infiltrating cells (macrophages) are the primary producers of IL-1β within the CNS and, through the use of an in vitro BBB model, that IL-1β promotes CXCR4-mediated T cell adhesion to brain microvasculature endothelial cells (BMECs). Of interest, IFNγ+ and CD69+ WNV-primed T cells were able to overcome CXCL12-mediated adhesion via down-regulation of CXCR4. These data indicate that infiltrating IL-1β-producing leukocytes contribute to cellular interactions at endothelial barriers that impart protective CNS inflammation by regulating the parenchymal entry of CXCR4+ virus-specific T cells during WNV infection.

Regional astrocyte IFN signaling restricts pathogenesis during neurotropic viral infection

“…As previous studies have suggested that early WNV neuroinvasion can be caused by defects in BBB function (4,27,28), we determined whether BBB permeability was altered differentially in the cerebellum and cerebral cortex of Cre -littermate controls. Analysis of extravasation of sodium fluorescein (376 Da) on various days following s.c. infection showed biphasic kinetics, as observed in our previous studies (4,21), with an enhancement of BBB permeability on day 4 after infection, decreased permeability on days 5 and 6, and a reopening of the BBB on day 8 ( Figure 1H). While loss of IFNAR signaling in astrocytes led to enhancement of BBB permeability in both cerebral cortical and cerebellar tissues after infection, the kinetics of these effects differed between regions.…”

“…This enhanced BBB permeability is associated with earlier detection of WNV in hindbrain regions of the CNS, suggesting that astrocyte IFNAR signaling prevents or delays infection at this site. Altered expression of cytokines such as IL-1β also probably influences other functions of the BBB, including local antigen presentation (21,45) and perivascular capture of infiltrating leukocytes (9,46), as reflected by the broad parenchymal localization of CD3 + lymphocytes in our study. Regional differences in astrocyte signaling may also differentially impact regional differences in other neurovascular cell types, including endothelial cells.…”

“…Leukocytes were isolated from freshly dissected CNS regions following PBS perfusion and stained with fluorescently conjugated antibodies to CD3, CD4, CD8β, CD11b, F4/80, and CD45 as previously described (21). Intracellular IFN-γ staining was performed on isolated leukocytes in an I-A b -restricted NS3-2066 and NS3-1616 peptide and a D b -restricted NS4B peptide restimulation assay as previously described (27).…”

“…Neurons are by far the preferred cellular target of WNV throughout the CNS (12,18,19); in contrast, infection of glial cells in vivo has not been well documented in mice and is probably rare (20). However, astrocyte activation and gliosis has been observed in vivo during WNV infection (9,21). Given the findings from our own studies demonstrating that IFNAR signaling in astrocytes enhances in vitro BBB integrity in response to WNV (4), we used Ifnar fl/fl Gfap-Cre mice, in which IFNAR signaling was abrogated in glial fibrillary acidic protein-expressing (GFAP-expressing) astrocytes, to evaluate the contribution of astrocyte IFNAR signaling to WNV pathogenesis and disease.…”

Encephalitic Arboviruses: Emergence, Clinical Presentation, and Neuropathogenesis

“…Elimination of virus-infected cells in the CNS requires a CD8 T-cell response [233][234][235][236]. In response to WNVand JEV infections, neurons release CXCL10, which is required for recruitment of CD8 T cells into the brain via the C-X-C chemokine receptor (CXCR)3 [151,170].…”