Rabies virus (RV) induces encephalomyelitis in humans and animals. However, the pathogenic mechanism of rabies is not fully understood. To investigate the host responses to RV infection, we examined and compared the pathology, particularly the inflammatory responses, and the gene expression profiles in the brains of mice infected with wild-type (wt) virus silver-haired bat RV (SHBRV) or laboratory-adapted virus B2C, using a mouse genomic array (Affymetrix). Extensive inflammatory responses were observed in animals infected with the attenuated RV, but little or no inflammatory responses were found in mice infected with wt RV. Furthermore, attenuated RV induced the expression of the genes involved in the innate immune and antiviral responses, especially those related to the alpha/beta interferon (IFN-␣/␤) signaling pathways and inflammatory chemokines. For the IFN-␣/␤ signaling pathways, many of the interferon regulatory genes, such as the signal transduction activation transducers and interferon regulatory factors, as well as the effector genes, for example, 2-5-oligoadenylate synthetase and myxovirus proteins, are highly induced in mice infected with attenuated RV. However, many of these genes were not up-regulated in mice infected with wt SHBRV. The data obtained by microarray analysis were confirmed by real-time PCR. Together, these data suggest that attenuated RV activates, while pathogenic RV evades, the host innate immune and antiviral responses.Rabies virus (RV) is a nonsegmented negative-stranded RNA virus of the Rhabdoviridae family and induces a fatal neurological disease in humans and animals (15). Although significant advances have been made in rabies prevention and control, the disease remains a major threat to public health and continues to cause numerous human deaths around the world. The dog remains the most important reservoir in Asia, Africa, and Latin America, where most human rabies cases occur (19). In the United States, dog rabies has been largely brought under control through pet vaccination programs, and there have been only a few incidents where large carnivores have transmitted rabies directly to humans (11,26). Most of the human cases in the past decade have been associated with RV found in bats, particularly silver-haired bats (11,18,39,47). Furthermore, most of the cases occurred without a history of exposure (11), suggesting that the silver-haired bat RV (SHBRV) is highly pathogenic and neuroinvasive (18,47).RV invades the nervous system by binding to neural receptors, such as acetylcholine receptor (31), neural cell adhesion molecule (52), or nerve growth factor receptor (NTR75) (53). Then, RV is transported to the central nervous system (CNS) by retrograde transportation, possibly by binding to cytoplasmic dynein (29,46). Despite extensive investigation in the past 100 years, the pathogenic mechanisms by which street (wildtype [wt]) RV infection results in neurological diseases and death in humans are not well understood. This is because there is very little neuronal pathology or d...

The structural alterations of neuronal processes in mice were investigated after the mice were infected with rabies virus (RV). Silver staining of infected brain sections showed severe destruction and disorganization of neuronal processes in mice infected with pathogenic RV but not with attenuated RV. However, neuronal bodies showed very little pathological changes. Electron microscopy revealed the disappearance of intracellular organelles, as well as the disappearance of synaptic structures and vesicles. Infection of primary neurons with pathogenic, but not attenuated, RV resulted in the destruction of neuronal processes and disappearance of microtubule-associated protein 2 and neurofilament immunoreactivity, which suggests that pathogenic RV causes degeneration of neuronal processes possibly by interrupting cytoskeletal integrity.Despite extensive investigation, the mechanism by which rabies virus (RV) infection causes neurological disease and death is still not completely understood (3). RV enters the peripheral nervous system at the bite site by binding to one or more specific neural receptors (14,22,25) with or without local replication (19,21). Once inside neurons, RV is spread by retrograde transport to the spinal cord and then to the brain (4, 12). Clinical signs include severe agitation, depression, hydrophobia, and paralysis followed by impaired consciousness and coma (9). Patients eventually die of circulatory insufficiency, cardiac arrest, and respiratory failure (9, 23). Despite the dramatic and severe clinical course, postmortem examination of rabies patients reveals only a few pathological lesions, such as cerebral edema (18). Inflammatory reactions and other histological lesions are mild with relatively little neuronal loss (15, 18). These observations led to the hypothesis that fatal rabies may result from neuronal dysfunction rather than neuronal damage (24).Studies of neuronal dysfunction have revealed electroencephalographic abnormalities, including the disappearance of rapid eye movement sleep and the development of pseudoperiodic facial myoclonus (6). Brain electrical activity terminated about 30 min before cardiac arrest, indicating that cerebral death in experimental rabies occurs prior to failure of vegetative functions (6, 7). RV infection of neurons also induces dysfunction of ion channels, for example, reduction in sodium channels and inward rectifier potassium channels (10, 11), which could prevent infected neurons from firing action potentials and generating synaptic potentials, resulting in functional impairment. Decreased binding of serotonin (particularly the subtype 5-HT 1D ) to its receptors has also been reported (2). Recent studies of the release of norepinephrine, dopamine, and serotonin in the hippocampi of rats infected with RV indicated that at the terminal stage of the disease, neurons are no longer capable of releasing neurotransmitters at the synaptic junctions (5). Hence, there is evidence of impaired release of neurotransmitters and binding of neurotransmitters to th...

Induction of apoptosis by rabies virus (RV) has been reported to be associated with the expression of the glycoprotein (G), but inversely correlated with pathogenicity. To further delineate the association between the expression of the G and the induction of apoptosis, recombinant RVs with replacement of only the G gene were used to infect mice by the intracerebral route. Recombinant viruses expressing the G from attenuated viruses expressed higher level of the G and induced more apoptosis in mice than recombinant RV expressing the G from wild-type (wt) or pathogenic RV, demonstrating that it is the G gene that determines the level of G expression and, consequently, the induction of apoptosis. Likewise, recombinant viruses expressing the G from wt or pathogenic RV are more pathogenic in mice than those expressing G from attenuated RV, confirming the inverse correlation between RV pathogenicity and the induction of apoptosis. To investigate the mechanism by which induction of apoptosis attenuates viral pathogenicity, mice were infected with wt or attenuated RV by the intramuscular route. It was found that low doses of attenuated RV induced apoptosis in the spinal cord and failed to spread to the brain or produce neurological disease. On the other hand, apoptosis was not observed in the spinal cord of mice infected with the same doses of wt RV and the virus spread to various parts of the brain and induced fatal neurologic disease. These results suggest that glycoprotein-mediated induction of apoptosis limits the spread of attenuated rabies viruses in the central nervous system (CNS) of mice.

Respiratory syncytial virus (RSV) is a primary cause of morbidity and life-threatening lower respiratory tract disease in infants and young children. Children with acute RSV bronchiolitis often develop respiratory sequelae, but the disease mechanisms are poorly understood. Mounting evidence suggests that RSV may mediate persistent infection. Using immunohistochemistry to identify RSV and RSV-infected cell types, we show that RSV infects primary neurons and neuronal processes that innervate the lungs through a process that involves RSV G protein and the G protein CX3C motif. These findings suggest a mechanism for disease chronicity and have important implications for RSV disease intervention strategies.