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Powassan Viruses Spread Cell to Cell during Direct Isolation from Ixodes Ticks and Persistently Infect Human Brain Endothelial Cells and Pericytes.

ABSTRACT: Powassan viruses (POWVs) are neurovirulent tick-borne flaviviruses emerging in the northeastern United States, with a 2% prevalence in Long Island (LI) deer ticks (Ixodes scapularis). POWVs are transmitted within as little as 15 min of a tick bite and enter the central nervous system (CNS) to cause encephalitis (10% of cases are fatal) and long-term neuronal damage. POWV-LI9 and POWV-LI41 present in LI Ixodes ticks were isolated by directly inoculating VeroE6 cells with tick homogenates and detecting POWV-infected cells by immunoperoxidase staining. Inoculated POWV-LI9 and LI41 were exclusively present in infected cell foci, indicative of cell to cell spread, despite growth in liquid culture without an overlay. Cloning and sequencing establish POWV-LI9 as a phylogenetically distinct lineage II POWV strain circulating in LI deer ticks. Primary human brain microvascular endothelial cells (hBMECs) and pericytes form a neurovascular complex that restricts entry into the CNS. We found that POWV-LI9 and -LI41 and lineage I POWV-LB productively infect hBMECs and pericytes and that POWVs were basolaterally transmitted from hBMECs to lower-chamber pericytes without permeabilizing polarized hBMECs. Synchronous POWV-LI9 infection of hBMECs and pericytes induced proinflammatory chemokines, interferon-β (IFN-β) and proteins of the IFN-stimulated gene family (ISGs), with delayed IFN-β secretion by infected pericytes. IFN inhibited POWV infection, but despite IFN secretion, a subset of POWV-infected hBMECs and pericytes remained persistently infected. These findings suggest a potential mechanism for POWVs (LI9/LI41 and LB) to infect hBMECs, spread basolaterally to pericytes, and enter the CNS. hBMEC and pericyte responses to POWV infection suggest a role for immunopathology in POWV neurovirulence and potential therapeutic targets for preventing POWV spread to neuronal compartments. IMPORTANCE We isolated POWVs from LI deer ticks (I. scapularis) directly in VeroE6 cells, and sequencing revealed POWV-LI9 as a distinct lineage II POWV strain. Remarkably, inoculation of VeroE6 cells with POWV-containing tick homogenates resulted in infected cell foci in liquid culture, consistent with cell-to-cell spread. POWV-LI9 and -LI41 and lineage I POWV-LB strains infected hBMECs and pericytes that comprise neurovascular complexes. POWVs were nonlytically transmitted basolaterally from infected hBMECs to lower-chamber pericytes, suggesting a mechanism for POWV transmission across the blood-brain barrier (BBB). POWV-LI9 elicited inflammatory responses from infected hBMEC and pericytes that may contribute to immune cell recruitment and neuropathogenesis. This study reveals a potential mechanism for POWVs to enter the CNS by infecting hBMECs and spreading basolaterally to abluminal pericytes. Our findings reveal that POWV-LI9 persists in cells that form a neurovascular complex spanning the BBB and suggest potential therapeutic targets for preventing POWV spread to neuronal compartments.

SUBMITTER: Conde JN

PROVIDER: S-EPMC8754205 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Candidatus Rickettsia vini was originally detected in Ixodes arboricola ticks from Spain, and subsequently reported from several other Western Palearctic countries including Belgium. Recently, the bacterium was isolated in mammalian (Vero) cell culture from macerated male I. arboricola from Czech Republic, but there have been no reports of propagation in tick cells. Here we report isolation in a tick cell line of three strains of Ca. R. vini from I. arboricola collected from nests of great tits (Parus major) in Belgium. Internal organs of one male and two engorged female ticks were dissected aseptically, added to cultures of the Rhipicephalus microplus cell line BME/CTVM23 and incubated at 28?°C. Rickettsia-like bacteria were first seen in Giemsa-stained cytocentrifuge smears between 2 and 15 weeks later. Two of the isolates grew rapidly, destroying the tick cells within 2-4 weeks of onward passage in BME/CTVM23 cells, while the third isolate grew much more slowly, only requiring subculture at 4-5-month intervals. PCR amplification of bacterial 16S rRNA and Rickettsia gltA, sca4, ompB, ompA and 17-kDa genes revealed that all three isolates were Ca. R. vini, with 100 % identity to each other and to published Ca. R. vini sequences from other geographical locations. Transmission electron microscopy revealed typical single Rickettsia bacteria in the cytoplasm of BME/CTVM23 cells. The Ca. R. vini strain isolated from the male I. arboricola tick, designated Boshoek1, was tested for ability to grow in a panel of Ixodes ricinus, Ixodes scapularis and R. microplus cell lines and in Vero cells. The Boshoek1 strain grew rapidly, causing severe cytopathic effect, in the R. microplus line BME26, the I. ricinus line IRE11 and Vero cells, more slowly in the I. ricinus line IRE/CTVM19, possibly established a low-level infection in the I. ricinus line IRE/CTVM20, and failed to infect cells of any of four I. scapularis lines over a 12-week observation period. This study confirmed the applicability of the simple tick organ-cell line co-cultivation technique for isolation of tick-borne Rickettsia spp. using BME/CTVM23 cells.

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Powassan Viruses Spread Cell to Cell during Direct Isolation from Ixodes Ticks and Persistently Infect Human Brain Endothelial Cells and Pericytes.

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