Temporal sequence of viral antigen expression in the cochlea induced by cytomegalovirus

Zika virus infection causes widespread damage to the inner ear

Zika virus (ZIKV) has been recently recognized as a causative agent of newborn microcephaly, as well as other neurological consequences. A less well recognized comorbidity of prenatal ZIKV infection is hearing loss, but cases of hearing impairment following adult ZIKV infection have also been recognized. Diminished hearing following prenatal ZIKV infection in a mouse model has been reported, but no cellular consequences were observed. We examined the effects of ZIKV infection on inner ear cellular integrity and expression levels of various proteins important for cochlear function in type I interferon receptor null (Ifnar1^-/-) mice following infection at 5-6 weeks of age. We show that ZIKV antigens are present in cells within the cochlear epithelium, lateral wall, spiral limbus and spiral ganglion. Here we show that ZIKV infection alters cochlear expression of genes that signal cell damage (S100B), transport fluids (AQP1), are gaseous transmitters (eNOs) and modulate immune response (F4/80). Morphological analyses shows that not only are cochlear structures compromised by ZIKV infection, but damage also occurs in vestibular end organs. ZIKV produces a graded distribution of cellular damage in the cochlea, with greatest damage in the apex similar to that reported for cytomegalovirus (CMV) infection. The graded distribution of damage may indicate a differential susceptibility to ZIKV along the cochlear tonotopic axis. Collectively, these data are the first to show the molecular and morphological damage to the inner ear induced by ZIKV infection in adults and suggests multiple mechanisms contributing to the hearing loss reported in the human population.

Cytomegalovirus-induced pathology in human temporal bones with congenital and acquired infection

OBJECTIVE

Publications on histopathology of human temporal bones with cytomegalovirus (CMV) infection are limited. We aim to determine histopathology of the inner ears and the middle ears in human temporal bones with congenital and acquired CMV infections.

METHODS

Temporal bones from 2 infants with congenital and 2 adults with acquired CMV infection were evaluated by light microscopy.

RESULTS

Two infants with congenital CMV infection showed striking pathological changes in the inner ear. There was a hypervascularization of the stria vascularis in the cochlea of the first infant, but no obvious loss of outer and inner hair cells was seen in the organ of Corti. However, cytomegalic cells and a loss of outer hair cells were found in the cochlea of the second infant. The vestibular organs of both infants showed cytomegalic cells, mostly located on dark cells. There was a loss of type I and type II hair cells in the macula of the saccule and utricle. Loss of hair cells and degeneration of nerve fibers was also seen in the semicircular canals. Both infants with congenital infection showed abundant inflammatory cells and fibrous structures in the middle ear cavity. No evidence of cytomegalic cells and hair cell loss was found in the cochlea or vestibular labyrinth in acquired CMV infection.

CONCLUSIONS

In two infants with congenital CMV infection, the cochlea, vestibule, and middle ear were highly affected. Temporal bones of adult donors with acquired viral infection showed histological findings similar to donors of the same age without ear disease.

Guinea Pig Cytomegalovirus (GPCMV): A Model for the Study of the Prevention and Treatment of Maternal-Fetal Transmission

A major public health challenge today is the problem of congenital cytomegalovirus (CMV) transmission. Maternal-fetal CMV infections are common, occurring in 0.5-2% of pregnancies, and these infections often lead to long-term injury of the newborn infant. In spite of the well-recognized burden that these infections place on society, there are as yet no clearly established interventions available to prevent transmission of CMV. In order to study potential interventions, such as vaccines or antiviral therapies, an animal model of congenital CMV transmission is required. The best small animal model of CMV transmission is the guinea pig cytomegalovirus (GPCMV) model. This article summarizes the GPCMV model, putting it into the larger context of how studies in this system have relevance to human health. An emphasis is placed on how the vertical transmission of GPCMV recapitulates the pathogenesis of congenital CMV in infants, making this a uniquely well-suited model for the study of potential CMV vaccines.

Induction of cytomegalovirus-infected labyrinthitis in newborn mice by lipopolysaccharide: a model for hearing loss in congenital CMV infection

Congenital cytomegalovirus (CMV) infection is the most common infectious cause of sensorineural hearing loss in children. Here, we established an experimental model of hearing loss after systemic infection with murine CMV (MCMV) in newborn mice. Although almost no viral infection was observed in the inner ears and brains by intraperitoneal (i.p.) infection with MCMV in newborn mice, infection in these regions was induced in combination with intracerebral (i.c.) injection of bacterial lipopolysaccharide (LPS). The susceptibility of the inner ears was higher than that of the brains in terms of viral titer per unit weight. In the labyrinths, the viral infection was associated with the mesenchymal vessels and accompanied by inflammatory cells induced by LPS, causing hematogenous targets of infection in the labyrinths. Viral infection also spread in the perilymph regions such as the scala tympani and scala vestibuli, probably from infected brains via meningogenic and cochlear nerve routes. Viral infection was not observed in the scala media in the endolymph, including the Corti organ. However, viral infection was observed in the spiral limbus, including the stria vascularis. These results suggest that hearing loss caused by labyrinthitis after congenital CMV infection may be enhanced by inflammation caused by systemic bacterial infection in the neonatal period.

Pathogenesis of cytomegalovirus-associated labyrinthitis in a guinea pig model

Cytomegalovirus infects fetuses through the placenta, resulting in various congenital disorders in newborns, including hearing loss. We developed a monoclonal antibody to guinea pig cytomegalovirus (GPCMV) that was available for immunohistochemistry, and investigated the expression of the GPCMV antigen in animal models of direct and congenital infections. Injection of GPCMV, directly to the inner ear, increased the sound pressure level and resulted in labyrinthitis with severe inflammation. Immunohistochemistry detected GPCMV-infected cells mainly in the scala tympani, scala vestibule and spinal ganglion, but rarely in the cochlear duct. Injection of GPCMV to 5-week pregnant guinea pigs resulted in severe labyrinthitis in fetuses. Immunohistochemistry detected GPCMV-infected cells in the perilymph area and spinal ganglion, but not in the endolymph area, including hair cells. These data suggest that the virus spreads via the perilymph and neural routes in the inner ear of both models of direct and congenital infections.

The pathology of the temporal bones of a child with acquired cytomegalovirus infection: studies by light microscopy, immunohistochemistry and polymerase-chain reaction

STUDY DESIGN

The first case of an acquired cytomegalovirus (CMV) infection of the inner ear is reported in a 3-year-old girl in remission from acute lymphocytic leukemia.

METHODS

Horizontal sections of the temporal bones were studied by light microscopy and immunohistological staining by avidin-biotin-complex-technique was performed on selected archival sections. Three sections were processed for detection of the virus genome by the polymerase chain reaction (PCR).

RESULTS

By light microscopy the epithelium of the endolymphatic sac, the utricle and the semicircular canals showed deeply stained acidophilic inclusions and the stria vascularis had a loose structure especially in the intermediate layer. The changes were limited to the non-sensory parts of the labyrinth and no CMV type cells were observed in the organ of Corti. There was a loss of inner and outer hair cells and loss of cochlear ganglion cells caused by either the virus or treatment with gentamicin. Standard immunohistochemistry failed to demonstrate staining with CMV antibodies, but PCR, demonstrated CMV-DNA in one section.

CONCLUSION

Molecular techniques may be able to detect acquired CMV infections in archival pediatric bones temporal bones. The histologic findings in the labyrinth were milder, however showed some similarity to children with congenital CMV labyrinthitis.

Characterization of an experimentally induced inner ear immune response

OBJECTIVE

To determine the effects of a sterile immune response on the structure and function of the cochlea.

METHODS

An immune response was created in guinea pigs by systemically sensitizing the animals to keyhole limpet hemocyanin and subsequently challenging the inner ear with the protein. Animals were allowed to survive for 1 to 5 weeks, after which the cochlea was evaluated histologically. Hearing was measured by auditory brainstem response before the inner ear challenge, during the survival period, and prior to sacrifice.

RESULTS

Inflammatory cells infiltrated the cochlea from the circulation. Surface preparations and plastic sections of the organ of Corti 1 and 2 weeks after the initiation of the inflammation demonstrated degeneration of the sensory and supporting cells in cochlear turns containing inflammatory cells. Good preservation of structures was seen in the more apical cochlear turns with little or no inflammatory cells. In cochleas from animals that survived 5 weeks, most of the infiltrated cells were cleared after undergoing apoptosis and the inflammatory matrix in the scala tympani began to calcify. Hearing loss was moderate to severe depending on the amount of inflammation.

CONCLUSION

Although in general the immune response serves to protect an organism from infection, these results demonstrate that bystander injury associated with local immune responses in the cochlea, an organ incapable of regeneration, causes permanent cochlear destruction and hearing loss.

Late sequelae of cochlear infection

Inflammatory reactions within the inner ear are deleterious to cochlear function and can result in server hearing loss that does not recover. This study investigated a guinea pig model of long-term cytomegalovirus infection. At high doses active inflammation was still present after 35 days. At lower doses some ears showed partial resolution while others were still inflamed. Hearing was totally lost in all cases of persistent inflammation. There was some residual hearing in the cases that had resolved. Cochlear structures including the organ of Corti, stria vascularis, and spiral ganglion were partially degenerated. Fibrotic matrix within scala tympani was ossified in many cases. These changes are consistent with those described for human cochleas following putative viral infections.

Spiral modiolar vein: its importance in viral load of the inner ear

Guinea pig-specific cytomegalovirus and Sendai virus were inoculated into the cochleas of seronegative guinea pigs to study the route of entry of cells participating in inner ear inflammation. Inflammatory cells accumulated around the spiral modiolar vein and appeared to be streaming from this vein into the scala tympani via a collecting venule. Inactivated virus inoculated into the cochlea and normal control cochlea failed to show inflammatory cell infiltrates. The spiral modiolar vein appears to play an important role in the movement of cells from the systemic circulation into the inner ear as part of the host's normal defense against invading pathogens such as viruses.

Spiral modiolar vein: its importance in inner ear inflammation

The inner ear responds immunologically to foreign proteins and pathogens introduced into the cochlea. The route of entry of the cells participating in the inner ear inflammatory process is the spiral modiolar vein with its collecting venules. Since this vein is located adjacent to the scala tympani, the end result of cellular infiltration is fibro-osseous obliteration of this scala preferentially. This observation has implications for the placement of cochlear implant electrodes of patients with labyrinthitis as the cause of hearing loss.

Effects of cyclophosphamide on the pathogenesis of cytomegalovirus-induced labyrinthitis

Cyclophosphamide was used in this study to define the contribution of the inflammatory response relative to direct cytopathic effects of guinea pig cytomegalovirus (GPCMV) in inducing sensorineural hearing loss in the guinea pig. The eighth nerve compound action potential (CAP) threshold on day 7 after inoculation of GPCMV into the scala tympani was an average of 35 dB greater for control animals than for those that were immunosuppressed with daily intraperitoneal injections of cyclophosphamide (20 mg/kg body weight). The amount of GPCMV antigen in the cochlea, detected immunohistochemically did not correlate with the CAP threshold. However, the greater the inflammatory response to GPCMV in the cochlea, the higher the CAP threshold and thus the greater the hearing loss. This study demonstrates that the inflammatory response to GPCMV may be more important than direct cytopathic effects of the virus in producing sensorineural hearing loss in GPCMV-induced labyrinthitis.

Spiral modiolar vein: its importance in inner ear inflammation

The inner ear responds immunologically to foreign proteins and pathogens introduced into the cochlea. The route of entry of the cells participating in the inner ear inflammatory process is the spiral modiolar vein with its collecting venules. Since this vein is located adjacent to the scala tympani, the end result of cellular infiltration is fibro-osseous obliteration of this scala preferentially. This observation has implications for the placement of cochlear implant electrodes of patients with labyrinthitis as the cause of hearing loss.

Immunologic responses in experimental cytomegalovirus labyrinthitis

To better understand the pathogenesis of cytomegalovirus labyrinthitis, a guinea pig model was created. Following inoculation at several sites (cardiac, perilymph, and endolymphatic sac) in both seronegative and seropositive animals, the immunologic, histologic, and electrophysiologic responses were measured. Seronegative animals uniformly showed progressive hearing loss with marked inflammation and degeneration of neural elements. In animals inoculated into the endolymphatic sac, an associated endolymphatic hydrops developed in addition to deafness. Seropositivity protected the hearing, but endolymphatic sac inoculations resulted in mild hydrops due to local inflammation that was devoid of evidence of viral replication. The question of whether hearing loss was attributable to local inflammatory responses rather than the cytopathic effects of the virus was then examined. To test this hypothesis, animals were immunosuppressed with cyclophosphamide prior to intracochlear inoculation of cytomegalovirus. The immunosuppressed animals showed significantly better hearing than the controls, and this correlated directly with the degree of cellular infiltration of the scala tympani. These studies confirm the importance of host immune responses in the pathogenesis of hearing loss due to cytomegalovirus.

Experimental congenital cytomegalovirus labyrinthitis and sensorineural hearing loss

Cytomegalovirus is a leading cause of human congenital viral infection and hearing loss. The pathogenesis of human congenital cytomegalovirus infection is poorly understood. We have developed a reproducible model of congenital cytomegalovirus-induced sensorineural hearing loss in guinea pigs. This report reviews our previously published results and provides additional new information about this model.

Guinea pig cytomegalovirus immediate-early transcription

Guinea pig cytomegalovirus (GPCMV) immediate-early (IE) gene expression was analyzed. GPCMV IE RNA was defined as RNA obtained from GPCMV-infected guinea pig cells treated with cycloheximide for 1 h before infection and for 4 h postinfection. Mapping studies showed that GPCMV IE genes are located at several distinct sites on the GPCMV genome. A total of 17 GPCMV IE transcripts were identified, and 9 IE transcripts coded for by three specific regions of the genome (regions I, II, and III) were characterized in detail. A series of recombinant DNA clones were generated to identify the nine IE transcripts. Three of the IE transcripts from region I and three from region III were transcribed in the same direction from overlapping sequences. The 2.0-kilobase (kb) transcript encoded by the EcoRI E DNA fragment (region II) was the most abundant IE GPCMV transcript. The cloned GPCMV DNA subfragment that was used to identify the region II EcoRI E 2.0-kb transcript did not hybridize to GPCMV early or late RNA, indicating that this transcript is expressed only under IE conditions. Expression of RNAs from the IE genes was also measured during a natural GPCMV infection in the absence of cycloheximide. During the natural infection, the transcripts previously identified under IE cycloheximide block conditions were expressed, and the region II EcoRI E 2.0-kb transcript was the most abundant transcript at 1 h postinfection. In addition, a rise and fall in RNA levels was observed during the natural infection, demonstrating the transient nature of expression of these transcripts. We conclude that GPCMV IE gene expression is complex, involving a reasonably large number of genes, and demonstrates some similarities with IE transcription by other CMVs.

The role of macrophages in the disposal of degeneration products within the organ of corti after acoustic overstimulation

We analysed the ultrastructure of scavenger cells in the organ of Corti of 10 guinea pigs at five different intervals (5 min, 4 h, 24 h, 5 days and 28 days) after acoustic overstimulation. There was evidence of phagocytic cells only at 5 days after noise exposure. Dendritic macrophages were seen phagocytosing degenerating cells and debris in the tunnel of Corti and in the region of the outer hair cells. Transforming monocytes in this area and leukocytic accumulation within the spiral lamina vessel suggest that these cells may be derived from blood-borne monocytes. These cells may contribute to local disposal of intracochlear cell degeneration products and thus to healing of organ of hearing after induction of noise-induced damage.