Abstract
Characterizing the mechanisms by which West Nile virus (WNV) causes blood-brain barrier (BBB) disruption, leukocyte infiltration into the brain and neuroinflammation is important to understand the pathogenesis of WNV encephalitis. Here, we examined the role of endothelial cell adhesion molecules (CAMs) in mediating the adhesion and transendothelial migration of leukocytes across human brain microvascular endothelial cells (HBMVE). Infection with WNV (NY99 strain) significantly induced ICAM-1, VCAM-1, and E-selectin in human endothelial cells and infected mice brain, although the levels of their ligands on leukocytes (VLA-4, LFA-1and MAC-1) did not alter. The permeability of the in vitro BBB model increased dramatically following the transmigration of monocytes and lymphocytes across the models infected with WNV, which was reversed in the presence of a cocktail of blocking antibodies against ICAM-1, VCAM-1, and E-selectin. Further, WNV infection of HBMVE significantly increased leukocyte adhesion to the HBMVE monolayer and transmigration across the infected BBB model. The blockade of these CAMs reduced the adhesion and transmigration of leukocytes across the infected BBB model. Further, comparison of infection with highly neuroinvasive NY99 and non-lethal (Eg101) strain of WNV demonstrated similar level of virus replication and fold-increase of CAMs in HBMVE cells suggesting that the non-neuropathogenic response of Eg101 is not because of its inability to infect HBMVE cells. Collectively, these results suggest that increased expression of specific CAMs is a pathological event associated with WNV infection and may contribute to leukocyte infiltration and BBB disruption in vivo. Our data further implicate that strategies to block CAMs to reduce BBB disruption may limit neuroinflammation and virus-CNS entry via ‘Trojan horse’ route, and improve WNV disease outcome.
Highlights
Since its introduction to the United States in 1999, West Nile virus (WNV), a mosquito-borne flavivirus classified as an NIAID Category B Priority Pathogen, has emerged as a leading cause of viral encephalitis, with more than 5,000 cases including nearly 250 deaths in 2012
To further delineate the role of WNV infectedleukocytes versus -endothelial cells in blood-brain barrier (BBB) disruption, we conducted parallel experiments using the transmigration of either WNV-infected monocytes at day 2 after infection across the uninfected BBB models (Fig. 1A) or uninfected monocytes across the WNV-infected BBB models at day 3 after infection (Fig. 1B)
These results suggest that WNV infection of leukocytes did not contribute significantly to the loss of resistance of the in vitro BBB model, rather it is the infection of BBB endothelial cells that mediated the disruption of the integrity of the BBB
Summary
Since its introduction to the United States in 1999, West Nile virus (WNV), a mosquito-borne flavivirus classified as an NIAID Category B Priority Pathogen, has emerged as a leading cause of viral encephalitis, with more than 5,000 cases including nearly 250 deaths in 2012. WNV is an enveloped positive stranded RNA virus and is closely related to other human pathogens including dengue, yellow fever, Japanese encephalitis and tick-borne encephalitis viruses. WNV infection triggers effective innate immune responses, which collectively mediate virus clearance from the periphery and control its dissemination in the brain, in subset of patients WNV enters the central nervous system (CNS) [3]. WNV neuropathogenesis is mainly dependent on the ability of the virus to enter the brain and replicate within resident cells including neurons and astrocytes [3]. Leukocytes entering the CNS must cross the blood-brain barrier (BBB) and one of the routes of WNV-CNS entry is proposed to be via ‘Trojan horse’ mechanism by infected leukocytes [5]
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