Spongiform degeneration induced by neuropathogenic murine coronavirus infection

Abstract

Soluble receptor-resistant mutant 7 (ssr7) is isolated from a highly neurovirulent mouse hepatitis virus (MHV) JHMV cl-2 strain (cl-2). srr7 exhibits lower virulence than its maternal strain in infected mice, which is typically manifested in a longer lifespan. In this study, during the course of infection with srr7, small spongiotic lesions became apparent at 2 days post-inoculation (pi), they spread out to form spongiform encephalopathy by 8 to 10 days pi. We recently reported that the initial expressions of viral antigens in the brain are detected in the infiltrating monocyte lineage and in ependymal cells. Here, we demonstrate that the next viral spread was observed in glial fibrillary acidic protein-positive cells or nestin-positive progenitor cells which take up positions in the subventricular zone (SVZ). From this restricted site of infection in the SVZ, a large area of gliosis extended deep into the brain parenchyma where no viral antigens were detected but vacuolar degeneration started at 48 h pi of the virus. The extremely short incubation period compared with other experimental models of infectious spongiform degeneration in the brain would provide a superior experimental model to investigate the mechanism of spongiotic lesions formation.

Extracellular matrix in the CNS induced by neuropathogenic viral infection

“…Mixed primary cultures on eight‐well plastic chamber slides (Nalge Nunc International, Rochester , NY, USA) were fixed in cold ethanol for 1 min followed by fixation in cold acetone for 5 min. Immunostaining was carried out using antibodies for collagen type I (ColI) (Calbiochem, San Diego, CA, USA), ColIV (SouthernBiotech, Birmingham, AL, USA), ColVI (Abcam, Tokyo, Japan), and interferon β (IFNβ) (PBL Interferon Source, Piscataway, NJ, USA), in addition to the antibodies and reagents previously described, such as antibodies to detect MHV‐JHM, ERag, laminin, ColIII, podoplanin, neurons, oligodendrocytes, GFAP and appropriate secondary antibodies, and reagents such as biotin‐conjugated streptavidin, and Hoechst 33342 for nuclear staining. Fluorescence was visualized with a confocal laser scanning microscope (Leica Microsystems, Heidelberg, Germany) to obtain images of double or triple immunostaining and three‐dimensional constructs, as previously described .…”

“…Most mice infected with srr7 survive for 8 days after infection. The viral antigens are predominantly detected in the white matter, and neurons are not infected . The virulence of Mu‐3 is intermediate between that of cl‐2 and srr7, showing a mixed pattern of the neuropathologies of cl‐2 and srr7 .…”

“…In spite of these differences in virulence and neuropathological findings, the viruses exhibit a similar pattern of viral spread during the initial phase of infection. Between 12 and 24 hpi, viral antigens are detected only in the meninges, followed by viral spread into the ventricular wall at 24 to 48 hpi before invasion into the brain parenchyma, indicating that the viruses use a passage between the meninges and ventricular wall as an entry route into the brain parenchyma …”

Contribution of Lewis X Carbohydrate Structure to Neuropathogenic Murine Coronaviral Spread

“…srr7 induces spongiotic lesions in areas where no viral antigens are detectable during the early phase of infection (6), without prominent inflammation, but with elevated levels of proinflammatory cytokines in the infected brain (9). Damage of neurons in the hippocampus was reported to result from bystander effects of infection with Mu-3, a mutant isolated from srr7 (10), and another kind of virus, such as Theiler' s murine encephalomyelitis virus (TMEV) (11).…”

“…The viral antigens in the brain are detectable in the white matter. However, the neuropathological characteristics are not demyelinating inflammation, but spongiosis, which appears 48 hours post-inoculation (hpi) (6). Initial viral antigens, after inoculation with either cl-2 or srr7, are detectable in CD11b-or F4/80-positive monocytes/ macrophages (Mo/Mas) that have infiltrated the meninges.…”