The emergence of human metapneumovirus

Imaging analysis of human metapneumovirus-infected cells provides evidence for the involvement of F-actin and the raft-lipid microdomains in virus morphogenesis

Backgound

Due to difficulties of culturing Human metapneumovirus (HMPV) much of the current understanding of HMPV replication can be inferred from other closely related viruses. The slow rates of virus replication prevent many biochemical analyses of HMPV particles. In this study imaging was used to examine the process of HMPV morphogenesis in individually infected LLC-MK2 cells, and to better characterise the sites of HMPV assembly. This strategy has circumvented the problems associated with slow replication rates and allowed us to characterise both the HMPV particles and the sites of HMPV morphogenesis.

Methods

HMPV-infected LLC-MK2 cells were stained with antibodies that recognised the HMPV fusion protein (F protein), attachment protein (G protein) and matrix protein (M protein), and fluorescent probes that detect GM1 within lipid-raft membranes (CTX-B-AF488) and F-actin (Phalloidin-FITC). The stained cells were examined by confocal microscopy, which allowed imaging of F-actin, GM1 and virus particles in HMPV-infected cells. Cells co-expressing recombinant HMPV G and F proteins formed virus-like particles and were co-stained with antibodies that recognise the recombinant G and F proteins and phalloidin-FITC and CTX-B-AF594, and the distribution of the G and F proteins, GM1 and F-actin determined.

Results

HMPV-infected cells stained with anti-F, anti-G or anti-M revealed a filamentous staining pattern, indicating that the HMPV particles have a filamentous morphology. Staining of HMPV-infected cells with anti-G and either phalloidin-FITC or CTX-B-AF488 exhibited extensive co-localisation of these cellular probes within the HMPV filaments. This suggested that lipid-raft membrane domains and F-actin structures are present at the site of the virus morphogenesis, and are subsequently incorporated into the HMPV filaments. Furthermore, the filamentous virus-like particles that form in cells expressing the G protein formed in cellular structures containing GM1 and F-actin, suggesting the G protein contains intrinsic targeting signals to the sites of virus assembly.

Conclusions

These data suggest that HMPV matures as filamentous particles and that virus morphogenesis occurs within lipid-raft microdomains containing localized concentrations of F-actin. The similarity between HMPV morphogenesis and the closely related human respiratory syncytial virus suggests that involvement of F-actin and lipid-raft microdomains in virus morphogenesis may be a common feature of the Pneumovirinae.

Electronic supplementary material

The online version of this article (doi:10.1186/s12985-014-0198-8) contains supplementary material, which is available to authorized users.

Evidence for the interaction of the human metapneumovirus G and F proteins during virus-like particle formation

BACKGROUND

Human metapneumovirus (HMPV) is now a major cause of lower respiratory infection in children. Although primary isolation of HMPV has been achieved in several different cell lines, the low level of virus replication and the subsequent recovery of low levels of infectious HMPV have hampered biochemical studies on the virus. These experimental methodologies usually require higher levels of biological material that can be achieved following HMPV infection. In this study we demonstrate that expression of the HMPV F, G and M proteins in mammalian cells leads to HMPV virus-like particles (VLP) formation. This experimental strategy will serve as a model system to allow the process of HMPV virus assembly to be examined.

METHODS

The HMPV F, G and M proteins were expressed in mammalian cell lines. Protein cross-linking studies, sucrose gradient centrifugation and in situ imaging was used to examine interactions between the virus proteins. VLP formation was examined using sucrose density gradient centrifugation and electron microscopy analysis.

RESULTS

Analysis of cells co-expressing the F, G and M proteins demonstrated that these proteins interacted. Furthermore, in cells co-expression the three HMPV proteins the formation VLPs was observed. Image analysis revealed the VLPs had a similar morphology to the filamentous virus morphology that we observed on HMPV-infected cells. The capacity of each protein to initiate VLP formation was examined using a VLP formation assay. Individual expression of each virus protein showed that the G protein was able to form VLPs in the absence of the other virus proteins. Furthermore, co-expression of the G protein with either the M or F proteins facilitated their incorporation into the VLP fraction.

CONCLUSION

Co-expression of the F, G and M proteins leads to the formation of VLPs, and that incorporation of the F and M proteins into VLPs is facilitated by their interaction with the G protein. Our data suggests that the G protein plays a central role in VLP formation, and further suggests that the G protein may also play a role in the recruitment of the F and M proteins to sites of virus particle formation during HMPV infection.

Human metapneumovirus in patients with respiratory tract infection in Kuwait

Human metapneumovirus (hMPV) has been recognized as an important cause of respiratory tract infections in all age groups and in all geographical area. The role of hMPV in causing respiratory tract infections in Kuwait was not yet investigated. The aim of this study was to determine the prevalence of hMPV infection in Kuwait among patients with respiratory tract infection with respect to other respiratory viruses. During January–December 2009, 460 respiratory samples from 388 patients with respiratory tract infection were collected from different hospitals. They were tested for hMPV RNA by real‐time PCR, and for other respiratory viruses by conventional PCR. Out of 388 patients, 110 (28%) were positive for viral respiratory infections; 21 (5.4%) were positive for hMPV, 29 (7.5%) were positive for rhinovirus, 13 (4%) were positive for respiratory syncytial virus, and 10 (3%) were positive for adenovirus. Most (n = 19, 90.5%) of hMPV‐positive patients were admitted to the intensive care unit, 76% of them were of age 2 years and below, and 24% of age 59 years and above. All hMPV‐positive elderly patients had pneumonia while 50% of hMPV‐positive infants had bronchopneumonia. Children with hMPV/rhinovirus co‐infection (n = 3, 1%) had recurrent chest infection and frequent intensive care unit admission. The hMPV infection was mostly detected between December and May, and genotype B was more prevalent than genotype A. This is the first study demonstrating the prevalence of hMPV infection in Kuwait, and suggests that hMPV infection is prevalent in infants and elderly patients with lower respiratory tract infection. J. Med. Virol. 83:1811–1817, 2011. © 2011 Wiley‐Liss, Inc.

Evaluation of the PrimerDesign™ genesig real-time reverse transcription-polymerase chain reaction assay and the INFINITI® Respiratory Viral Panel Plus assay for the detection of human metapneumovirus in Kuwait

Human metapneumovirus (hMPV) is a respiratory pathogen that was discovered in 2001 and is considered a major cause of both upper and lower respiratory tract infections. A sensitive, fast, and high-throughput diagnostic test is needed for the detection of hMPV that may assist in the clinical management as well as in the reduction of inappropriate therapy. Therefore, a comparison assessment was performed in this study between the PrimerDesign™ genesig real-time reverse transcription–polymerase chain reaction (RT-PCR) Assay and the INFINITI^® Respiratory Viral Panel Plus Assay (RVP-Plus) for the detection of hMPV infection in patients with respiratory tract infections. A total of 200 respiratory samples were collected from 185 hospitalized patients, during the winter season in Kuwait. Of 185 patients, 10 (5.4%) were positive for hMPV RNA by the in-house RT-PCR assay, while 7 (4%) were positive for hMPV RNA by the real-time RT-PCR assay and 9 (5%) were positive for hMPV RNA by the INFINITI^® RVP-Plus assay. The high incidence rate (60%) of hMPV infection was in January 2011. The sensitivity of the real-time RT-PCR and INFINITI^® RVP-Plus assays was 70% and 90%, respectively, with specificity of 100% for both assays. hMPV types A and B could be identified in this study; however, discordant genotyping results were found between the direct sequencing method and the INFINITI^® RVP-Plus assay in 33% of hMPV-positive patients.

Pneumonia in the immunocompetent patient

Pneumonia is an acute inflammation of the lower respiratory tract. Lower respiratory tract infection is a major cause of mortality worldwide. Pneumonia is most common at the extremes of life. Predisposing factors in children include an under-developed immune system together with other factors, such as malnutrition and over-crowding. In adults, tobacco smoking is the single most important preventable risk factor. The commonest infecting organisms in children are respiratory viruses and Streptoccocus pneumoniae. In adults, pneumonia can be broadly classified, on the basis of chest radiographic appearance, into lobar pneumonia, bronchopneumonia and pneumonia producing an interstitial pattern. Lobar pneumonia is most commonly associated with community acquired pneumonia, bronchopneumonia with hospital acquired infection and an interstitial pattern with the so called atypical pneumonias, which can be caused by viruses or organisms such as Mycoplasma pneumoniae. Most cases of pneumonia can be managed with chest radiographs as the only form of imaging, but CT can detect pneumonia not visible on the chest radiograph and may be of value, particularly in the hospital setting. Complications of pneumonia include pleural effusion, empyema and lung abscess. The chest radiograph may initially indicate an effusion but ultrasound is more sensitive, allows characterisation in some cases and can guide catheter placement for drainage. CT can also be used to characterise and estimate the extent of pleural disease. Most lung abscesses respond to medical therapy, with surgery and image guided catheter drainage serving as options for those cases who do not respond.