Meningeal Immunity and Viral Neuropathogenesis

SUMMARY Emerging and re-emerging neurotropic viruses, including flaviviruses and alphaviruses, generally cause fever, malaise, and related symptoms. However, in some patients, these viruses enter the central nervous system (CNS) and cause severe illness and disease resulting in meningitis, encephalitis, and death. Several cellular mechanisms have been described that allow viruses to bypass the blood-brain barrier. However, to date, there have been no anatomical routes identified that enable direct passage of virions in the periphery into the CNS. This highly collaborative and interactive proposal between the Diamond and Kipnis laboratories will advance our mechanistic understanding of how meningeal structures function in the regulation of and response to neurotropic virus infections. Our overarching hypothesis is that neurotropic viruses can directly enter the CNS through arachnoid cuff exit (ACE) points, a newly described meningeal structure linking the CNS and periphery. We hypothesize that neurotropic virus infections early-in-life alter the development of meningeal immunity, and this increases the severity of and vulnerability to heterologous neurotropic virus infections later in life. We will address our hypotheses in four specific aims: (1) We will define the role of arachnoid cuff exit (ACE) points in neurotropic flavivirus entry into the CNS and provide a detailed transcriptional profile of meningeal and brain responses to neurotropic flavivirus infection at different ages (e.g., in utero, neonatal and adult); (2) We will determine how early-life neurotropic virus infection and IFN-g signaling modulates the development of meningeal lymphatic vessels; (3) We will test the contribution of IFN-g signaling in meningeal stromal cells to ACE point development in the context of early-life neurotropic virus infection; and (4) We will define the effects of early-in-life neurotropic virus infection (with Zika virus [ZIKV], a TORCH pathogen) on the neuropathogenesis of a second, heterologous neurotropic virus in adulthood. Conceptually, we will define the role of newly described meningeal structures in viral entry into the CNS. Mechanistically, we will explore how virus-induced IFN-g signaling modulates the development of meningeal immunity and its subsequent impact on neurotropic virus infection. Our suite of relevant neurotropic flavivirus and alphavirus mouse models (e.g., ZIKV, WNV, VEEV, WEEV), novel inducible Cre-driver mouse lines enabling targeting of specific cell types in the meninges (e.g., arachnoid barrier cells, Dpp4-CreERT2; dural border cells, Slc47a1-CreERT2) and state-of-the- art immunological assays of meningeal structure and function will enable us to define how meningeal immunity is affected by and modulates the neuroinvasion and neuropathogenesis of virus infection. Together, our team will elucidate the mechanisms and reciprocal relationships between CNS invasion by neurotropic viruses and meningeal immune responses, which could provide new targets for therapeutic intervention against neurotropic viruses.