ABSTRACT
This review highlights recent advances in how the innate and adaptive immune systems control the blood-brain barrier (BBB) and the blood-nerve barrier (BNB). Interferons and TAM receptors play key roles in innate immune control of the BBB. Cells of the adaptive immune system, particularly CD4+ T cells, take distinct routes to enter neural tissues and mediate immune surveillance. Furthermore, T cell-mediated opening of the BBB and the BNB is crucial to allow antibody access and thereby block the replication of neurotropic viruses. Such novel insights gained from basic research provide key foundations for future design of therapeutic strategies - enabling antibody access to the brain may be key to cancer immunotherapy and to the use of vaccines against neurodegenerative conditions such as Alzheimer's disease.
Subject(s)
Adaptive Immunity , Antibodies/immunology , Blood-Brain Barrier/immunology , Blood-Nerve Barrier/immunology , Immunity, Innate , Animals , Blood-Brain Barrier/pathology , Blood-Brain Barrier/virology , Blood-Nerve Barrier/pathology , Blood-Nerve Barrier/virology , Brain Neoplasms/immunology , Brain Neoplasms/pathology , Brain Neoplasms/therapy , Humans , Immunotherapy , Interferons/immunology , Neurodegenerative Diseases/immunology , Neurodegenerative Diseases/pathology , Neurodegenerative Diseases/therapy , Receptor Protein-Tyrosine Kinases/immunology , T-Lymphocytes/immunology , Virus Diseases/immunology , Virus Diseases/pathology , Viruses/immunologyABSTRACT
West Nile virus (WNV) is an important emerging neurotropic virus, responsible for increasingly severe encephalitis outbreaks in humans and horses worldwide. However, the mechanism by which the virus gains entry to the brain (neuroinvasion) remains poorly understood. Hypotheses of hematogenous and transneural entry have been proposed for WNV neuroinvasion, which revolve mainly around the concepts of blood-brain barrier (BBB) disruption and retrograde axonal transport, respectively. However, an overrepresentation of in vitro studies without adequate in vivo validation continues to obscure our understanding of the mechanism(s). Furthermore, WNV infection in the current rodent models does not generate a similar viremia and character of CNS infection, as seen in the common target hosts, humans and horses. These differences ultimately question the applicability of rodent models for pathogenesis investigations. Finally, the role of several barriers against CNS insults, such as the blood-cerebrospinal fluid (CSF), the CSF-brain and the blood-spinal cord barriers, remain largely unexplored, highlighting the infancy of this field. In this review, a systematic and critical appraisal of the current evidence relevant to the possible mechanism(s) of WNV neuroinvasion is conducted.
Subject(s)
Encephalitis, Viral/virology , Gene Expression Regulation, Viral , Viral Proteins/genetics , Viremia/virology , Virus Internalization , West Nile virus/metabolism , Adherens Junctions/metabolism , Adherens Junctions/virology , Animals , Blood-Brain Barrier/metabolism , Blood-Brain Barrier/virology , Blood-Nerve Barrier/metabolism , Blood-Nerve Barrier/virology , Brain/pathology , Brain/virology , Cell Adhesion Molecules/genetics , Cell Adhesion Molecules/metabolism , Encephalitis, Viral/physiopathology , Horses , Humans , Spinal Cord/pathology , Spinal Cord/virology , Tight Junctions/metabolism , Tight Junctions/virology , Viral Proteins/metabolism , Viremia/physiopathology , West Nile virus/genetics , West Nile virus/pathogenicityABSTRACT
Viral infections are a major cause of human disease. Although most viruses replicate in peripheral tissues, some have developed unique strategies to move into the nervous system, where they establish acute or persistent infections. Viral infections in the central nervous system (CNS) can alter homeostasis, induce neurological dysfunction and result in serious, potentially life-threatening inflammatory diseases. This Review focuses on the strategies used by neurotropic viruses to cross the barrier systems of the CNS and on how the immune system detects and responds to viral infections in the CNS. A special emphasis is placed on immune surveillance of persistent and latent viral infections and on recent insights gained from imaging both protective and pathogenic antiviral immune responses.