Mice lacking α1,3-fucosyltransferase 9 exhibit modulation of in vivo immune responses against pathogens.

Carbohydrate structures, including Lewis X (Le(x)), which is not synthesized in mutant mice that lack α1,3-fucosyltransferase 9 (Fut9(-/-)), are involved in cell-cell recognition and inflammation. However, immunological alteration in Fut9(-/-) mice has not been studied. Thus, the inflammatory response of Fut9(-/-) mice was examined using the highly neurovirulent mouse hepatitis virus (MHV) JHMV srr7 strain. Pathological study revealed that inflammation induced in the brains of Fut9(-/-) mice after infection was more extensive compared with that of wild-type mice, although viral titers obtained from the brains of mutant mice were lower than those of wild-type mice. Furthermore, the reduction in cell numbers in the spleens of wild-type mice after infection was not observed in the infected Fut9(-/-) mice. Although there were no clear differences in the levels of cytokines examined in the brains between Fut9(-/-) and wild-type mice except for interferon-ß expression, some of those in the spleens, including interferon-γ, interleukin-6, and monocyte chemoattractant protein 1, showed higher levels in Fut9(-/-) than in wild-type mice. Furthermore, Fut9(-/-) mice were refractory to the in vivo inoculation of endotoxin (LPS) compared with wild-type mice. These results indicate that Le(x) structures are involved in host responses against viral or bacterial challenges.

Spongiform degeneration induced by neuropathogenic murine coronavirus infection.

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.

Cytopathy of an infiltrating monocyte lineage during the early phase of infection with murinecoronavirus in the brain.

Viral spread during the early stages after infection was compared between a highly neurovirulent mouse hepatitis virus (MHV), JHMV cl-2 strain (cl-2), and its low-virulent mutant, soluble-receptor-resistant (srr)7. The infection of cells with srr7 (soluble-receptor-resistant mutant 7) is dependent on a known MHV receptor (MHVR), carcinoembryonic cell adhesion molecule 1a, whereas cl-2 shows MHVR-independent infection. Initial viral antigens were detected between 12 and 24 h post-inoculation (p.i) in the infiltrating cells that appeared in the subarachnoidal space of mouse brains infected with viruses. There were no significant differences in the intensity or spread of viral antigens in the inflammatory cells between the two viruses. However, 48 h after infection with cl-2, viral antigen-positive cells in the grey matter with the shape of neurons, which do not express MHVR, were detected, while srr7 infection was observed primarily in the white matter. Some of the viral antigen-positive inflammatory cells found in the subarachnoidal space during the early phase of infection reacted with anti-F4/80 or anti-CD11b monoclonal antibodies. Syncytial giant cells (SGCs) expressing viral and CD11b antigens were also detected among these inflammatory cells. These antigen-positive cells appeared in the subarachnoidal space prior to viral antigen spread into the brain parenchyma, indicating that viral encephalitis starts with the infection of infiltrating monocytes which express MHVR. Furthermore, the observation indicates that viral infection has cytopathic effects on the monocyte lineage, which plays a critical role in innate immunity, leading to the rapid spread of viruses during the early stage of infection.

Mutant murine hepatitis virus-induced apoptosis in the hippocampus.

The mutant virus Mu-3 was isolated from the soluble receptor-resistant mutant 7 virus (srr7), which is a neuropathogenic strain of the mouse hepatitis virus JHMV, and cloned as a soluble receptor-resistant mutant from the highly neuropathogenic JHMV strain cl-2 virus (cl-2). In order to identify specific characteristics of Mu-3, the pathology of Mu-3-infected mice was compared with that of srr7- and cl-2-infected mice. The neuropathology after Mu-3 infection exhibited a mixed pattern comparable to that induced by srr7 and cl-2 infections. In addition, Mu-3 infection caused marked apoptotic lesions in the hippocampal region, particularly in the CA2 and CA3 subregions, in the brains of all infected mice. In contrast, in cl-2 infection, 10-20% of the infected mice exhibited apoptosis in the hippocampus, which was primarily observed in the CA1 subregion. Apoptosis also occurred in the pyramidal neurons and CD11b-bearing cells. The apoptotic cells, indicated by caspase 3-activation, were a mixed population of infected and a higher number of uninfected cells. These data indicated that apoptosis observed in Mu-3 infection could be induced by the indirect effects of infection in addition to direct effects of the infected cells occurring in a cell-autonomous manner.

Characterization of splenic cells during the early phase of infection with neuropathogenic mouse hepatitis virus.

The highly neuropathogenic cl-2 and less virulent srr7 viruses isolated from the neurotropic JHM strain of the mouse hepatitis virus exhibit super acute spread of virus (SAS), a term applied when rapid viral spread from an organ or part of the initially infected site to another non-adjacent organ or part is detected within 12 h after infection. Herein, we used a cytospin procedure to confirm SAS in splenic cells derived from mice whose brains were infected with these viruses. The cytospin procedure enabled effective preservation of the cells on glass slides. With this method, we could characterize extremely low populations of infected cells in the spleen (less than 0.1%) at 12 h post-inoculation with srr7. We observed that all kinds of splenic cells examined were infected, including B220(+)Ly-6C(+) plasmacytoid dendritic cells. The population of viral antigen-positive splenic cells was only slightly higher in cl-2 infection than in srr7 infection, but the cells showing viral production were present in numbers significantly higher in cl-2 infection compared with srr7 infection.

Receptor-independent infection by mutant viruses newly isolated from the neuropathogenic mouse hepatitis virus srr7 detected through a combination of spinoculation and ultraviolet radiation.

The mouse hepatitis virus (MHV) has a high mutation rate, leading to various neuropathologies after infection. The srr7 mutant was isolated from the MHV strain cl-2, which induces characteristic spongiform degeneration in the brain. To investigate outcomes of srr7 infection, we re-cloned srr7(H2) from the viral stock srr7(Mix). During this re-cloning, we obtained the mutant viruses, Mu-1, Mu-2, and Br-1 which was isolated from the mice brain infected with srr7(Mix). We examined mutant viruses for infectivity independent of the major MHV receptor (MHVR), because these mutants exhibited high virulence similar to cl-2, which is MHVR-independent. To confirm MHVR-independence in vitro, we used a combination of spinoculation and ultraviolet radiation to detect distinct plaque formation (SpinoPlaque(UV+)) afrer infection of BHK cells, which do not express MHVR. Using this technique, we found that the unique neuropathologies caused by infection with the mutant viruses result from infecting neurons, which do not express MHVR. Infection with the mutant viruses was 100% correlated with SpinoPlaque(UV+) formation. This is in contrast to infection with srr7, which does not from SpinoPlaque(UV+).