ABSTRACT
Intracranial inoculation of susceptible strains of mice with the neuroadapted JHM strain of mouse hepatitis virus (JHMV, a member of the Coronaviridae family of viruses) results in an acute encephalomyelitis characterized by widespread growth of virus in astrocytes, microglia, and oligodendrocytes with relative sparing of neurons. Virus-specific CD4+ and CD8+ T cells infiltrate into the central nervous system in response to infection and control viral replication through secretion of interferon gamma as well as cytolytic activity. Nonetheless, virus persists in white matter tracts, and animals develop an immune-mediated demyelinating disease in which both T cells and macrophages amplify white matter damage. For the past decade, we have explored the therapeutic potential of human neural progenitor cells derived from pluripotent stem cells in promoting clinical recovery associated with remyelination of demyelinated axons following intraspinal transplantation. This chapter highlights recent studies from our laboratories demonstrating that tissue repair is associated with the emergence of regulatory T cells in response to transplantation of NPCs. © 2021 Elsevier Inc. All rights reserved.
ABSTRACT
Unlike SARS-CoV-1 and MERS-CoV, infection with SARS-CoV-2, the viral pathogen responsible for COVID-19, is often associated with neurologic symptoms that range from mild to severe, yet increasing evidence argues the virus does not ex-hibit extensive neuroinvasive properties. We demonstrate SARS-CoV-2 can infect and replicate in human iPSC-derived neurons and that infection shows limited antiviral and inflammatory responses but increased activation of EIF2 signaling following infection as determined by RNA sequencing. Intranasal infection of K18 human ACE2 transgenic mice (K18-hACE2) with SARS-CoV-2 resulted in lung pathology associated with viral replication and immune cell infiltration. In addition, similar to 50% of infected mice exhibited CNS infection characterized by wide-spread viral replication in neurons accompanied by increased expression of chemokine (Cxcl9, Cxcl10, Ccl2, Ccl5 and Ccl19) and cytokine (Ifn-lambda and Tnf-alpha) transcripts associated with microgliosis and a neuroinflammatory response consisting primarily of monocytes/macrophages. Micro-glia depletion via administration of colony-stimulating factor 1 receptor inhibitor, PLX5622, in SARS-CoV-2 infected mice did not affect survival or viral replication but did result in dampened expression of proinflammatory cytokine/chemokine transcripts and a reduction in monocyte/macrophage infiltration. These results argue that microglia are dispensable in terms of controlling SARS-CoV-2 replication in in the K18-hACE2 model but do contribute to an inflammatory response through expression of pro-inflammatory genes. Collectively, these findings contribute to previous work dem-onstrating the ability of SARS-CoV-2 to infect neurons as well as emphasizing the potential use of the K18-hACE2 model to study immunological and neuropathological aspects related to SARS-CoV-2-induced neurologic disease. IMPORTANCE Understanding the immunological mechanisms contributing to both host defense and disease following viral infection of the CNS is of critical importance given the increasing number of viruses that are capable of infecting and replicating within the nervous system. With this in mind, the present study was undertaken to evaluate the role of microglia in aiding in host defense following experimental infection of the central nervous system (CNS) of K18-hACE2 with SARS-CoV-2, the causative agent of COVID-19. Neurologic symptoms that range in severity are common in COVID-19 patients and understanding immune responses that contribute to restricting neurologic disease can provide important insight into better understanding consequences associated with SARS-CoV-2 infection of the CNS.