Mutant murine hepatitis virus-induced apoptosis in the hippocampus

Neurological involvement of COVID-19: from neuroinvasion and neuroimmune crosstalk to long-term consequences

As the coronavirus disease 2019 (COVID-19) pandemic continues to be a multidimensional threat to humanity, more evidence of neurological involvement associated with it has emerged. Neuroimmune interaction may prove to be important not only in the pathogenesis of neurological manifestations but also to prevent systemic hyperinflammation. In this review, we summarize reports of COVID-19 cases with neurological involvement, followed by discussion of possible routes of entry, immune responses against coronavirus infection in the central nervous system and mechanisms of nerve degeneration due to viral infection and immune responses. Possible mechanisms for neuroprotection and virus-associated neurological consequences are also discussed.

Pathology of Coronavirus Infections: A Review of Lesions in Animals in the One-Health Perspective

Coronaviruses (CoVs) are worldwide distributed RNA-viruses affecting several species, including humans, and causing a broad spectrum of diseases. Historically, they have not been considered a severe threat to public health until two outbreaks of COVs-related atypical human pneumonia derived from animal hosts appeared in 2002 and in 2012. The concern related to CoVs infection dramatically rose after the COVID-19 global outbreak, for which a spill-over from wild animals is also most likely. In light of this CoV zoonotic risk, and their ability to adapt to new species and dramatically spread, it appears pivotal to understand the pathophysiology and mechanisms of tissue injury of known CoVs within the "One-Health" concept. This review specifically describes all CoVs diseases in animals, schematically representing the tissue damage and summarizing the major lesions in an attempt to compare and put them in relation, also with human infections. Some information on pathogenesis and genetic diversity is also included. Investigating the lesions and distribution of CoVs can be crucial to understand and monitor the evolution of these viruses as well as of other pathogens and to further deepen the pathogenesis and transmission of this disease to help public health preventive measures and therapies.

Extracellular vesicles secreted by HBV-infected cells modulate HBV persistence in hydrodynamic HBV transfection mouse model

Hepatitis B, a viral infection that affects the liver, is thought to affect over 257 million people worldwide, and long-term infection can lead to life-threatening issues such as cirrhosis or liver cancer. Chronic hepatitis B develops by the interaction between hepatitis B virus (HBV) and host immune response. However, questions of how HBV-infected cells thwart immune system defenses remain unanswered. Extracellular vesicles (EVs) are used for cellular communication, carrying cargoes such as RNAs, proteins, and lipids and delivering them intracellularly after being endocytosed by target cells. HBV-infected liver cells secrete several types of EVs into body fluids such as complete and incomplete virions, and exosomes. We previously demonstrated that monocytes that incorporated EVs moved to immunoregulatory phenotypes via up-regulation of PD-L1, an immunocheckpoint molecule, and down-regulation of CD69, a leukocyte activation molecule. In this study, we transfected mice with HBV using hydrodynamic injection and studied the effects of EVs secreted by HBV-infected liver cells. EVs secreted from cells with HBV replication strongly suppressed the immune response, inhibiting the eradication of HBV-replicating cells in the mice transfected with HBV. EVs were systemically incorporated in multiple organs, including liver, bone marrow (BM), and intestine. Intriguingly, the BM cells that incorporated EVs acquired intestinal tropism and the dendritic cell populations in the intestine increased. These findings suggest that the EVs secreted by HBV-infected liver cells exert immunosuppressive functions, and that an association between the liver, bone marrow, and intestinal tract exists through EVs secreted from HBV-infected cells.

From conifers to cognition: Microbes, brain and behavior

A diversity of bacteria, protozoans and viruses ("endozoites") were recently uncovered within healthy tissues including the human brain. By contrast, it was already recognized a century ago that healthy plants tissues contain abundant endogenous microbes ("endophytes"). Taking endophytes as an informative precedent, we overview the nature, prevalence, and role of endozoites in mammalian tissues, centrally focusing on the brain, concluding that endozoites are ubiquitous in diverse tissues. These passengers often remain subclinical, but they are not silent. We address their routes of entry, mechanisms of persistence, tissue specificity, and potential to cause long-term behavioral changes and/or immunosuppression in mammals, where rabies virus is the exemplar. We extend the discussion to Herpesviridae, Coronaviridae, and Toxoplasma, as well as to diverse bacteria and yeasts, and debate the advantages and disadvantages that endozoite infection might afford to the host and to the ecosystem. We provide a clinical perspective in which endozoites are implicated in neurodegenerative disease, anxiety/depression, and schizophrenia. We conclude that endozoites are instrumental in the delicate balance between health and disease, including age-related brain disease, and that endozoites have played an important role in the evolution of brain function and human behavior.

IL-10 expression in pyramidal neurons after neuropathogenic coronaviral infection

The apoptosis of pyramidal neurons in CA2 and CA3 subregions of the hippocampus is induced after infection with Mu-3 virus (Mu-3), a neuropathogenic strain of the JHM virus (JHMV), at 4-5 days post-inoculation (dpi). The viral antigens in the hippocampus are mainly found in the CD11b-positive cells distributed in the stratum oriens located outside the pyramidal layer, and only a few pyramidal neurons are infected. Furthermore, the apoptotic cells, indicated as showing caspase 3 (Cas3) activation, consist of a high number of uninfected cells. Therefore, it is considered that the apoptotic lesions occur through the indirect effects of infection, and not as a result of direct infection with Mu-3, similar to the reported neuronal apoptosis in the hippocampus after other types of infection. The apoptosis in the pyramidal neurons is accompanied by various types of proinflammatory cytokines depending on the causative agents. Thus, the local expression of proinflammatory cytokines was studied, revealing no correlation in the distribution of cytokine expression with the subregions showing apoptosis. However, the anti-inflammatory cytokine IL-10 was produced by pyramidal neurons of CA2 and CA3 at 3 dpi when there is no destructive change or viral invasion in the hippocampus.

Extracellular matrix in the CNS induced by neuropathogenic viral infection

During the early phase of infection with an extremely neurovirulent murine coronavirus, cl-2, the ER-TR7 antigen (ERag)-positive fibers (ERfibs) associated with laminin and collagen III show a rapid increase in expression levels in the meninges, followed by an appearance of the antigens in the ventricle and brain parenchyma. Then, cl-2 invades the ventricle and ventricular wall along the newly assembled ERfibs after infection, using them as a pathway from the meninges, the initial site of infection. In the lymph nodes and spleen, ERag is mainly produced by fibroblastic reticular cells (FRCs), which play a key role in nursing the ERfibs to form a fibroblastic reticular network (FRN). The FRN functions as a conduit system to transfer antigens, cytokines or leukocytes in the lymphoid organs. In the brain parenchyma, astrocytes were found to produce the main components of mature ERfibs, such as collagen, laminin and ERag, which have been identified in the lymphoid organs. The producibility of these extracellular matrices (ECMs) by astrocytes was further confirmed by primary brain cultures, which disclosed the dissociation of laminin and ERag production, and the close association of ERag production with that of collagen, forming a fibrous structure. The pattern of ECM production in vitro indicated the process of forming mature ERfibs in the brain, that is, fibers made of collagen fibers and ERag are wrapped by laminin prepared as a sheet structure. In addition, the brain parenchymal cells that produce interferon β after infection in spite of their residence away from the sites of viral invasion were surrounded by ERfibs, which were closely associated with astrocytic fibers. These findings indicate that astrocytes play a central role in forming the astrocytic reticular network (ARN) in the brain parenchyma, as FRCs do to form FRN in the lymphoid organs.

Formation of fibroblastic reticular network in the brain after infection with neurovirulent murine coronavirus

cl‐2 virus is an extremely neurovirulent murine coronavirus. However, during the initial phase of infection between 12 and 24 h post‐inoculation (hpi), the viral antigens are detected only in the meninges, followed by viral spread into the ventricular wall before invasion into the brain parenchyma, indicating that the viruses employ a passage between the meninges and ventricular wall as an entry route into the brain parenchyma. At 48 hpi, the passage was found to be constructed by ER‐TR7 antigen (ERag)‐positive fibers (ERfibs) associated with laminin and collagen III between the fourth ventricle and meninges at the cerebellopontine angle. The construct of the fibers mimics the reticular fibers of the fibroblastic reticular network, which comprises a conduit system in the lymphoid organs. In the meninges, ERfibs together with collagen fibers, lining in a striped pattern, made up a pile of thin sheets. In the brain parenchyma, mature ERfibs associated with laminin were found around blood vessels. Besides mature ERfibs, immature Erfibs without associations with other extracellular matrix components like laminin and collagen appeared after infection, suggesting that the CNS creates a unique conduit system for immune communication triggered by viral invasion.

Contribution of Lewis X Carbohydrate Structure to Neuropathogenic Murine Coronaviral Spread

Although Lewis X (Le(x)), a carbohydrate structure, is involved in innate immunity through cell-to-cell and pathogen recognition, its expression has not been observed in mouse monocytes/macrophages (Mo/Mas). The Mo/Mas that infiltrate the meninges after infection with the neuropathogenic murine coronavirus strain srr7 are an initial target of infection. Furthermore, higher inflammatory responses were observed in gene-manipulated mice lacking α1,3-fucosyltransferase 9, which determines the expression of the Le(x) structure, than in wild type mice after infection. We investigated Le(x) expression using CD11b-positive peritoneal exudate cells (PECs) and found that Le(x) is inducible in Mo/Mas after infection with srr7, especially in the syncytial cells during the late phase of infection. The number of syncytial cells was reduced after treatment of the infected PECs with anti-Le(x) antibody, during the late phase of infection. In addition, the antibody treatment induced a marked reduction in the number of the infected cells at 24 hours post inoculation, without changing the infected cell numbers during the initial phase of infection. These data indicate that the Le(x) structure could play a role in syncytial formation and cell-to-cell infection during the late phase of infection.

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‐β (IFN‐β) expression, some of those in the spleens, including interferon‐γ (IFN‐γ), interleukin‐6 (IL‐6), and monocyte chemoattractant protein‐1 (MCP‐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.