Development and validation of an enzyme-linked immunosorbent assay for human metapneumovirus serology based on a recombinant viral protein

Detection of Antibodies Against Canine Circovirus in Naturally and Experimentally Infected Canines by Recombinant Capsid Enzyme-Linked Immunosorbent Assay

Canine circovirus (CanineCV), a new pathogen, was found to be associated with canine hemorrhagic diarrhea, vasculitis, granulomatous lymphadenitis, and acute gastroenteritis. Although CanineCV was highly positive rate in diarrhea cases, its pathogenicity remains controversial. In this study, the seroprevalence and associated risk factors of CanineCV infection among domestic dogs in northeastern China was investigated by an indirect enzyme-linked immunosorbent assay (iELISA) based on recombinant capsid protein. Results revealed the proposed iELISA had no cross-reactivity with other related pathogens, and yielded good diagnostic values. Then, to evaluate the rCap iELISA, this study applied it to detect antibodies against CanineCV in 1,047 clinical serum samples obtained from northeastern China in 2016–2017. Results showed the positive rates in the five cities of Jilin, Liaoning, and Heilongjiang provinces ranged from 22.22 to 42.29%. Statistical analysis shows a significant difference in age between dogs <3 months old with respect to the >1-year-old dogs (p = 0.005), that is, the CanineCV infection was more frequently identified from older dogs. In the artificially infected experiment, the dogs developed seroconversion after 9 or 12 days and the main way of virus excretion was through feces. More interestingly, among the 32 ELISA-positive serum samples, 34.75% samples tested positive for the CanineCV DNA by qPCR, far higher than that in ELISA-negative serum samples (5.26%, 2/38). This report is the first to demonstrate that CanineCV infection is common in the dog population in northeastern China. The results showed obvious differences in the positive rate associated with diarrhea, age, but not with different cities. This study also provide basis for evaluating the pathogenic potential of CanineCV. But, the pathogenicity, the relationship between antibody level and immune protection, and the harmful effects of this virus remain to be established.

A duplex recombinant viral nucleoprotein microbead immunoassay for simultaneous detection of seroresponses to human respiratory syncytial virus and metapneumovirus infections

Serologic diagnosis of human respiratory syncytial virus (hRSV) and human metapneumovirus (hMPV) infections has been shown to complement virus detection methods in epidemiologic studies. Enzyme immunoassays (EIAs) using cultured virus lysate antigens are often used to diagnose infection by demonstration of a ≥4-fold rises in antibody titer between acute and convalescent serum pairs. In this study, hRSV and hMPV nucleocapsid (recN) proteins were expressed in a baculovirus system and their performance compared with virus culture lysate antigen in EIAs using paired serum specimens collected from symptomatic children. The recN proteins were also used to develop a duplex assay based on the Luminex microbead-based suspension array technology, where diagnostic rises in antibody levels could be determined simultaneously at a single serum dilution. Antibody levels measured by the recN and viral lysate EIAs correlated moderately (hRSV, r(2)=0.72; hMPV, r(2)=0.76); the recN EIAs identified correctly 35 of 37 (94.6%) and 48 of 50 (96%) serum pairs showing diagnostic antibody rises by viral lysate EIAs. Purified recN proteins were then coupled to microbeads and serum pairs were tested at a single dilution on a Luminex MAGPIX(®) analyzer. The duplex recN assay identified correctly 33 of 39 (85%) and 41 of 47 (86.7%) serum pairs showing diagnostic rises to hRSV and hMPV, respectively. The recN assay permits simultaneous testing for acute hRSV and hMPV infections and offers a platform for expanded multiplexing of other respiratory virus assays.

Development of a luciferase immunoprecipitation system assay to detect IgG antibodies against human respiratory syncytial virus nucleoprotein

The nucleoprotein of respiratory syncytial virus (RSV-N) is immunogenic and elicits an IgG response following infection. The RSV-N gene was cloned into a mammalian expression vector, pREN2, and the expressed luciferase-tagged protein (Ruc-N) detected anti-RSV-N-specific IgG antibodies using a high-throughput immunoprecipitation method (the luciferase immunoprecipitation system [LIPS]-N(RSV) assay). The specificity of the assay was evaluated using monoclonal antibodies (MAbs) and monospecific pre- and postimmunization rabbit antisera. Blood serum samples from chimpanzees and humans with proven/probable RSV infection were also tested. The pre- and postimmunization serum samples from rabbits given human metapneumovirus (HMPV) or measles virus were negative when tested by the LIPS-N(RSV) assay, while antisera obtained after immunization with either the RSV-A or RSV-B strain gave positive signals in a dose-dependent manner. RSV-N MAb 858-3 gave a positive signal in the LIPS-N(RSV) assay, while MAbs against other paramyxovirus nucleoproteins or RSV-F or RSV-G did not. Serum samples from chimpanzees simultaneously immunized with vaccinia-RSV-F and vaccinia-RSV-G recombinant viruses were negative in the LIPS-N(RSV) assay; however, anti-RSV-N IgG responses were detected following subsequent RSV challenge. Seven of the 12 infants who were seronegative at 9 months of age had detectable anti-RSV-N antibodies when they were retested at 15 to 18 months of age. The LIPS-N(RSV) assay detects specific anti-RSV-N IgG responses that may be used as a biomarker of RSV infection.

Seroepidemiologies of human metapneumovirus and respiratory syncytial virus in young children, determined with a new recombinant fusion protein enzyme-linked immunosorbent assay

We compared antibodies against human metapneumovirus (HMPV) and respiratory syncytial virus (RSV) in children. The antibody nadirs for both viruses were at 3 to 5 months, and the majority of children were seropositive for both by 2 years. There was no significant difference in the kinetics of maternal antibody decline or seroconversion relative to the two viruses.

Human metapneumovirus in adults

Human metapneumovirus (HMPV) is a relative newly described virus. It was first isolated in 2001 and currently appears to be one of the most significant and common human viral infections. Retrospective serologic studies demonstrated the presence of HMPV antibodies in humans more than 50 years earlier. Although the virus was primarily known as causative agent of respiratory tract infections in children, HMPV is an important cause of respiratory infections in adults as well. Almost all children are infected by HMPV below the age of five; the repeated infections throughout life indicate transient immunity. HMPV infections usually are mild and self-limiting, but in the frail elderly and the immunocompromised patients, the clinical course can be complicated. Since culturing the virus is relatively difficult, diagnosis is mostly based on a nucleic acid amplification test, such as reverse transcriptase polymerase chain reaction. To date, no vaccine is available and treatment is supportive. However, ongoing research shows encouraging results. The aim of this paper is to review the current literature concerning HMPV infections in adults, and discuss recent development in treatment and vaccination.

Seroepidemiological study of human metapneumovirus in New Delhi, India

PURPOSE

There are a few seroepidemiological studies reported on human metapneumovirus (hMPV) as hMPV was only discovered in the year 2001. This respiratory virus has been reported to be ubiquitous and associated with respiratory tract infections in all age groups. The present study aimed at determining the prevalence of antibodies to hMPV in children and adults of 1 month to 55 years of age.

MATERIALS AND METHODS

Serum samples from 100 study subjects were tested for hMPV antibody by an in-house ELISA system that used hMPV-infected cell lysate antigen.

RESULT

The prevalence of antibody to hMPV was lowest in children less than 5 years of age (60%) and increased throughout age to > 80%. Similarly, geometric mean titres were 1:180 in children less than 5 years of age and reached a peak of 1:419 in adults over 35 years of age.

CONCLUSION

The results show that hMPV infection is acquired early in life and re-infection in later life may maintain the seroprevalence and antibody levels in adult population.

Recombinant expression and immunological characterisation of proteins derived from human metapneumovirus

BACKGROUND

Human metapneumovirus (HMPV) has been shown to cause respiratory infection, accounting for approximately 7% of all such disease, and contributes to the development of asthma in humans. HMPV has a worldwide distribution with infectivity rates approaching 100%, and immunocompromised patients are particularly at risk from viral exposure. No anti-HMPV vaccine is available and diagnosis is primarily based on in-house molecular or serological tests, in part due to limited availability of recombinant HMPV antigens.

OBJECTIVE

To generate a panel of HMPV-derived recombinant antigens, develop standardised ELISA systems for HMPV IgG detection and explore the nature of B cell memory against HMPV to underpin future vaccine studies.

STUDY DESIGN

HMPV viral RNA was isolated from a clinical specimen and RT-PCR was conducted. The HMPV M and P genes were cloned and expressed in Escherichia coli. The HMPV N gene was cloned and expressed in insect cells using the baculovirus expression system. Each purified recombinant antigens was subsequently employed in HMPV-specific ELISA.

RESULTS

High-level expression, and purification, of both HMPV matrix (M) (10 mg/g cells) and phosphoprotein (P) (3.82 mg/g cells) were achieved in an E. coli expression system. Recombinant HMPV (N) was successfully expressed in, and purified from the baculovirus expression system. Overall, a 99% HMPV IgG seroprevalence was observed (n = 96) using HMPV M-, N- and P-ELISA, respectively. The M antigen proved to be the most diagnostically useful with 99% of specimens tested exhibiting anti-M protein reactivity. A high correlation was observed between anti-M and N IgG reactivity (r = 0.96), with significant correlation also evident for anti-N and P IgG reactivity (r = 0.74). Lowest correlation was evident for anti-M and P IgG reactivity (r = 0.57). Finally, the first demonstration of HMPV-specific B cell memory (ranging 1-15 spot forming cells (SFC)/million cells) was achieved against M and P antigens in 40% of individuals tested.

CONCLUSION

This work describes robust diagnostic systems for HMPV and new insight into antigen-specific B cell memory against HMPV.

Large-scale seroprevalence analysis of human metapneumovirus and human respiratory syncytial virus infections in Beijing, China

Background

Human metapneumovirus (hMPV), a recently identified virus, causes acute respiratory tract infections (ARTIs) in infants and children. However, studies on the seroepidemeology of hMPV are very limited in China. To assess the seroprevalence of hMPV infection in China, we tested a total of 1,156 serum specimens for the presence of anti-hMPV IgG antibody in children and adults free of acute respiratory illness in Beijing, China by using hMPV nucleocapsid (N) protein as an antigen. As a control, we used the human serum antibody against the N protein of human respiratory syncytial virus (hRSV), the most important viral agent responsible for ARIs in children.

Results

The seropositive rate for hMPV increased steadily with age from 67% at 1-6 mo to 100% at age 20. However, the rate dropped slightly between 6 mo and 1 yr of age. The seropositive rate for hRSV also increased steadily with age from 71% at 1-6 mo to 100% at age 20. In children aged six months to six years, the seropositive rates for the anti-hRSV IgG antibody were significantly higher than those for hMPV. Additionally, IgG antibody titers to hMPV and hRSV were significantly higher in adults than in young children. Consistent with the seropositive rates, the geometric mean titer of anti-hMPV IgG antibody was lower than that of anti-hRSV IgG antibody in children aged six months to six years.

Conclusions

Our results indicate that similar to hRSV, exposure to hMPV is ubiquitous in the Beijing population. However, the seroprevalence of anti-hMPV IgG antibody is lower than that of hRSV in children between six months and six years old, which suggests a different number of repeat infections or a different response to infections.

Serum antibody response to respiratory syncytial virus F and N proteins in two populations at high risk of infection: children and elderly

Human respiratory syncytial virus (hRSV) is the main viral cause of severe respiratory infections in children and a common cause of morbidity in the elderly. The nucleocapsid (N) and fusion (F) proteins of hRSV were expressed in insect cells and used as antigens in two independent enzyme-linked immunosorbent assays (ELISAs) to measure the serum antibody response in two populations at high risk of hRSV infection, children and the elderly. Fifty-seven serum specimens from children aged from 1 to 10 years old and 91 sera from adults over 60 years old were tested. The ELISA results were compared with those obtained by an immunofluorescence assay (IFA) based on hRSV-infected cells, which was considered as the reference technique. Sensitivity and specificity were 94% and 85% for the N-ELISA and 86% and 81% for the F-ELISA, respectively. When the immune responses of the two groups of individuals were compared, it appeared that almost 100% of the elderly had antibodies against the N or F protein whereas only 50% of the sera from children had antibodies against either of the two viral proteins. In conclusion, the F and N ELISAs can be used successfully for detecting a specific antibody response to hRSV.

Development and evaluation of a whole virus-based enzyme-linked immunosorbent assay for the detection of human metapneumovirus antibodies in human sera

To apply serological testing for human metapneumovirus (hMPV) to large-scale sera samples, an enzyme-linked immunosorbent assay (ELISA) was developed in which purified virions were used as the antigen. The ELISA was evaluated using 102 human sera specimens from patients aged 0-59 years. There was a positive association between the ELISA results and neutralization test titers, with the correlation coefficients being greater in children <6 years old (rho=0.899, P<0.0001), which is consistent with a primary infection, than in persons >or=6 years old (rho=0.523, P<0.0001). Fifty sera samples were subjected to radioimmunoprecipitation to measure the quantity of antibodies to the fusion protein (RIP-F) and the nucleoprotein (RIP-N). The results showed significant associations between the ELISA titers and the amount of RIP-F as determined by radioimmunoprecipitation in children <6 years old (rho=0.804, P=0.0083) and in persons >or=6 years old (rho=0.577, P=0.0009). The correlation between the ELISA titer and the amount of RIP-N determined by radioimmunoprecipitation was not significant in persons >or=6 years old (rho=0.417, P=0.0829), although this correlation was significant in children <6 years old (rho=0.764, P=0.0137). The ELISA titer correlated with the amount of antibodies to the F protein, but not to the N protein. This whole virus-based ELISA will be useful for the diagnosis of hMPV infection in clinical laboratories and is also useful for the large-scale investigations, such as seroprevalence among residents of a particular region.

Review of new and newly discovered respiratory tract viruses in children

Respiratory tract viral infection continues to be among the most common reasons for emergency department visits and hospitalization of children, particularly infants younger than 1 year, in the United States. Throughout the years, clinicians have considered respiratory syncytial virus followed by influenza as the most common pathogens responsible. Over the past decade, new viruses have been discovered through both more specific testing and the finding of new agents causing infection. This includes human metapneumovirus, which leads to similar but often epidemiologically more severe clinical symptoms than respiratory syncytial virus. Other agents responsible for lower respiratory tract infection include Coronavirus (severe acute respiratory syndrome), Bocavirus, and others. This review serves to focus on some of the recent literature on these agents and the clinical impact they have on pediatric lung infection.

Human metapneumovirus and human bocavirus in children

Several new viruses have recently been described in children, including human metapneumovirus (hMPV) and human bocavirus (HBoV). hMPV has been established as a common cause of upper and lower respiratory tract infections in children, often second only to respiratory syncytial virus as a cause of bronchiolitis in infants. Diagnostic tools have been developed for the clinician and effective treatment and prevention strategies are being investigated. HBoV was more recently identified. Although it was initially identified in the airway of children, high rates of codetection of other viral pathogens and detection of the virus in the stool have raised questions about the true role of HBoV as a cause of respiratory infections. A focus on epidemiology, pathogenesis, clinical features, and diagnostic techniques for hMPV and HBoV is presented.

Human metapneumovirus: a new respiratory pathogen

Human metapneumovirus is a recently recognized pathogen of acute respiratory tract infection (ARI) in children as well as elderly and immunocompromised adults.The virus belongs to the family Paramyxoviridae, sub family Pneumovirinae and genus Metapneumovirus. Through genetic analysis it has been characterized into two groups A and B which are further divided into four sub-lineages. The virus is difficult to grow in tissue culture and hence reverse transcriptase-polymerase chain reaction (RT-PCR) for N and L gene is the method of choice for diagnosis. The virus has been seen in all countries with seasonal distribution in winter months for temperate and spring/summer for tropical countries. F gene is the most conserved among different lineages and efforts are underway to design recombination vaccine using F gene.

Human metapneumovirus reinfection among children in Thailand determined by ELISA using purified soluble fusion protein

BACKGROUND

Human metapneumovirus (hMPV) is a newly discovered paramyxovirus that causes acute respiratory illness. Despite apparent near-universal exposure during early childhood, immunity is transient.

METHODS

An indirect screening enzyme-linked immunosorbent assay using a recombinant soluble fusion (F) glycoprotein derived from hMPV was used to test for anti-F IgG in 1,380 pairs of acute- and convalescent-stage serum samples collected from children in Kamphaeng Phet, Thailand.

RESULTS

Of the 1,380 serum sample pairs tested, 1,376 (99.7%) showed evidence of prior infection with hMPV. Sixty-six paired specimens demonstrated a >or=4-fold rise in titer, for an overall reinfection rate of 4.9%. Two children demonstrated evidence of an initial infection. Forty-eight of the 68 new infections or reinfections occurred in 2000, accounting for 13.2% of all nonflaviviral febrile illnesses in the study population in that year. Of 68 positive cases, 85.3% complained of cough and 66.2% complained of rhinorrhea, compared with 61.4% and 49.0% of negative cases, respectively (P < .01). All positive samples were also tested for an increase in titer of antibodies to respiratory syncytial virus F, and 27% exhibited a >or=4-fold rise.

CONCLUSION

These results demonstrate that hMPV reinfections cause illness at a rate equal to that seen for initial infections. hMPV may have a more significant impact in older children than previously realized and may be the cause of significant outbreaks in this population.

The emergence of human metapneumovirus

Until relatively recently there had been episodes when children had been admitted into hospitals with symptoms that were similar to those expected for human respiratory syncytial virus (HRSV), but the available diagnostic procedures failed to detect the presence of HRSV, and the causative disease agent remained unidentified. Dutch scientists examined nasopharyngeal aspirates from similar patients in Holland using advanced molecular biology and imaging techniques. The conclusions of this study were published in 2001, revealing that a previously unidentified paramyxovirus was responsible for these infections. This agent was grouped within the subfamily Pneumovirinae, genus metapneumovirus, and given the name human metapneumovirus (HMPV) to distinguish it from other members of the genus Metapneumovirus that are of avian origin. Although HMPV is associated with upper respiratory tract infection, it is now recognized as a major cause of lower respiratory infection (LRTI) in children in a variety of different geographical regions. Furthermore, retrospective studies have detected the presence of HMPV in archived clinical material dating from the 1950s, suggesting that this was not a new virus, but it had remained undetected for several decades until its ‘emergence’ in 2001. This review will discuss the increasing global importance of HMPV as a cause of LRTI among young children.

Prospective evaluation of rapid antigen tests for diagnosis of respiratory syncytial virus and human metapneumovirus infections

Respiratory syncytial virus (RSV) and human metapneumovirus (hMPV) are two important viral pathogens that cause respiratory tract infections in the pediatric population. The rapid detection of these agents allows the prompt isolation and treatment of infected patients. In the present prospective study, we evaluated the performances of four rapid antigen detection assays, including a rapid chromatographic immunoassay (CIA) for RSV (Directigen EZ RSV; Becton Dickinson, Sparks, MD), a direct fluorescent-antibody assay (DFA) for RSV (Bartels; Trinity Biotech, Carlsbad, CA), and two DFAs for hMPV manufactured by Diagnostic Hybrids Inc. (DHI; Athens, OH) and Imagen (Oxoid Ltd., Basingstoke, Hampshire, United Kingdom). The clinical specimens tested comprised 515 nasopharyngeal aspirates submitted to the Clinical Microbiology Laboratory at Hartford Hospital from 1 November 2006 to 21 April 2007. Compared to the results of real-time reverse transcription-PCR (RT-PCR), the CIA had a sensitivity of 79.8% and a specificity of 89.5%. The RSV DFA with Bartels reagents showed a sensitivity of 94.1% and a specificity of 96.8%. For hMPV, the sensitivity and specificity were 62.5% and 99.8%, respectively, for the DHI DFA and 63.2% and 100%, respectively, for the Imagen DFA. The hands-on and test turnaround times for CIA were 10 and 30 to 60 min, respectively, and the hands-on and test turnaround times for the RSV and hMPV DFAs were 30 and 105 min, respectively. We conclude that while the RSV CIA is user-friendly, it lacks sensitivity and specificity, especially during off-peak months. In contrast, the RSV DFA is more sensitive and specific, but interpretation of its results is subjective and it demands technical time and expertise. Similarly, both hMPV DFAs are highly specific in comparison to the results of RT-PCR, but their sensitivities await further improvements.

Positive natural selection in the evolution of human metapneumovirus attachment glycoprotein

Human metapneumovirus (hMPV), a newly discovered virus of the family Paramyxoviridae, has been associated with upper and lower respiratory tract infections in different age groups in many countries. The putative attachment (G) glycoprotein of this virus was previously reported to have shown more extensive nucleotide and deduced amino acid sequence polymorphism than any other genomic regions of this virus, leading to four sub-lineages. Using a maximum likelihood-based codon substitution model of sequence evolution, here we report that sequences of extracellular domain of 8 amino acid sites in lineage 1a, and 3 amino acid sites each in lineage 1b, 2a, and 2b have a higher rate of nonsynonymous substitutions (d(N)) than the synonymous substitutions (d(S)) with a posterior probability above 0.95, thus suggesting the evidence of adaptive evolution driven by Darwinian selection. Although it is unclear whether these amino acid adaptations are driven by differential immune pressure or some other factors, identification of these positively selected amino acid sites would help in better screening using epitope mapping technology to identify and localize the sites that can be recognized by the immune system. We also observed surprisingly higher nucleotide substitution rates per site, per year for each lineage of hMPV than the rates that were previously reported for the human respiratory syncytial virus, suggesting rapid evolutionary dynamics of hMPV.

Seroprevalence of human metapneumovirus (hMPV) in the Canadian province of Saskatchewan analyzed by a recombinant nucleocapsid protein-based enzyme-linked immunosorbent assay

Human metapneumovirus (hMPV) is a newly identified respiratory virus associated with respiratory tract infection in both adults and children. Previous reports showed that infection of hMPV appeared to be ubiquitous. To determine the seroprevalence of hMPV, a total of 576 human sera from patients in Saskatchewan, Canada, were screened by enzyme-linked immunosorbent assay (ELISA) based on expression of the nucleocapsid (N) protein of hMPV in recombinant baculovirus. The recombinant N protein with a molecular mass of 43.5 kDa was abundantly produced in insect cells. Moreover, the recombinant N proteins of the prototype viruses for the two major groups of hMPV have cross-antigenicity. The seropositive rate for each age group was 13.5% (13/96) (0-5 years), 26.1% (25/96) (6-10 years), 32.3% (31/96) (11-15 years), 99.0% (95/96) (16-30 years), 91.7% (88/96) (31-60 years), and 93.8% (90/96) (61+ years), respectively. The data indicated that exposure to hMPV is a common phenomenon. The ELISA based on recombinant baculovirus produced N protein of hMPV provides a useful tool for seroepidemiological study of this virus.

Evaluation of ELISA based on the conserved and functional middle region of nucleocapsid protein to detect distemper infection in dogs

A 287bp fragment from the middle region of the nucleocapsid protein of canine distemper virus (CDV) was amplified from the conjunctival samples of distemper-infected dogs and was cloned into pRSET B vector. The recombinant protein was expressed as a 16-kDa-fusion protein with histidine tag in E. coli. Sera of distemper-infected and vaccinated dogs contained IgG antibodies against the purified recombinant protein as observed by enzyme linked immunosorbent assays (ELISA) and showed a strong correlation (r=0.882, p<0.0001 at 95% CI) and good agreement (kappa=0.718) with the conventional tissue culture viral antigen based ELISA. Further, the results of recombinant protein based ELISA and Western blotting with the sera from the infected and vaccinated dogs correlated well (kappa=0.8226). These findings recommend the use of the recombinant protein in the serodiagnosis of canine distemper virus infection in dogs.

Multi-year study of human metapneumovirus infection at a large US Midwestern Medical Referral Center

BACKGROUND

Because of its recent identification, few multi-year epidemiologic studies of hMPV infection have been reported.

OBJECTIVE

We sought to retrospectively describe hMPV infections among patients evaluated by a large US Midwestern referral laboratory.

STUDY DESIGN

Clinical specimens were submitted to a large US Midwest referral hospital from 1 October 2001 to 18 May 2004. RT-PCR was used to retrospectively screen the clinical specimens for human metapneumovirus. Demographic and clinical data were retrieved.

RESULTS

34 (2.6%) of 1294 specimens were hMPV positive. Among these, 21 (62%) were culture positive and available for genetic typing. A previously considered rare genotype of hMPV, B1, was the most common single genotype identified, comprising 9 (43%) of the 21 isolates. Multivariate logistic regression modeling identified patients aged 0.4-9 years (OR=8.9; 95% CI=2.0-38.5) and those under intensive care (OR=3.2; 95% CI=1.1-8.7) as more likely to have hMPV infection than their peers.

CONCLUSION

In this large referral hospital viral assays more often had evidence of hMPV when they were collected from children receiving intensive care.

Detection of antibodies against human metapneumovirus by Western blot using recombinant nucleocapsid and matrix proteins

Detection of antibodies against individual proteins of human metapneumovirus (hMPV) is important in the analysis of immune responses to hMPV. Specific antibodies against nucleocapsid (N) and matrix (M) proteins in 97 serum samples were tested by Western blot using recombinant N and M proteins of hMPV expressed in Escherichia coli. The results were compared with those of immunofluorescence assays (IFAs) based on hMPV-infected LLC-MK2 cells, which expressed the whole hMPV proteins. Thirty (61.2%) and 31 (63.3%) of 49 serum samples with titers of > or = 1:160 by IFA reacted with N and M proteins, respectively. Only 2 (4.2%) of 11 serum samples with titers of 1:80 by IFA reacted with N and M proteins. Antibodies against N and M proteins were not detected in 37 serum samples with titers of < 1:40 by IFA. These results indicate that the antibodies against N and M proteins are highly specific (100%) but less sensitive (42.1%, N protein; 40.8%, M protein) than those against whole proteins of hMPV detected by IFA. The reactivity of sera with the recombinant N protein and that with the recombinant M protein correlated well (correlation coefficient of 0.79), and the concordance of reactivities was 91% (kappa = 0.79). In summary, both recombinant N and M proteins of hMPV were antigenic, and the responses to N and M protein varied among patients. Therefore, Western blot using N and M proteins provide a useful tool for analysis of immune responses to hMPV.

Epidemiology of human metapneumovirus

Since the discovery of human metapneumovirus (hMPV) in 2001, the virus has been identified worldwide. hMPV is a common respiratory pathogen, particularly in infants and young children. The virus is associated with both upper and lower respiratory tract infections and may be a trigger for asthma. At least two major genotypes of hMPV circulate during community outbreaks. Whether these genotypes represent distinct serotypes remains controversial. The major challenges faced by the medical and scientific communities are the understanding of the pathogenesis of hMPV disease and the development of a safe and effective vaccine to protect against infection and disease caused by this newly recognized respiratory virus.

Human metapneumovirus in paediatric patients

Acute respiratory tract infections (ARTIs) are a leading cause of morbidity and mortality in children worldwide, but the aetiology of many ARTIs is still unknown. In 2001, researchers in The Netherlands reported the discovery of a previously unidentified pathogen called human metapneumovirus (hMPV). Since its initial description, hMPV has been associated with ARTI in Europe (Italy, France, Spain, the UK, Germany, Denmark, Finland and Norway), America (the USA, Canada, Argentina and Brazil), Asia (India, Japan, China and Singapore), Australia and South Africa in individuals of all ages. The incidence of infection varies from 1.5% to 25%, indicating that hMPV is a ubiquitous virus with a worldwide distribution. hMPV seems to play an important role as a cause of paediatric upper and lower respiratory tract infection, with similar, but not identical, epidemiological and clinical features to those of respiratory syncytial virus and influenza virus. Moreover, the socio‐economic impact of hMPV‐infected children on their families seems to be considerable, which suggests that, like influenza virus, hMPV infection may be a substantial public health problem for the community. It may be associated with significant morbidity and mortality in pre‐term infants and children with underlying clinical conditions, although more adequately controlled studies are needed to confirm its importance in such patients. Many fundamental questions concerning the pathogenesis of hMPV disease and the host's specific immune response remain to be answered. Further studies are also required to properly define hMPV diagnosis, treatment and prevention strategies.

Human Metapneumovirus Elicits Weak IFN-γ Memory Responses Compared with Respiratory Syncytial Virus

Human metapneumovirus (MPV) is a recently discovered pathogen that causes repeated lower respiratory tract infections beginning in infancy. The prevalence, nature and control of human regulatory responses to MPV are unknown. In this study, we develop and optimize systems to evaluate MPV-driven cytokine responses. Using primary culture of human PBMC from previously exposed adults, MPV-stimulated responses were directly compared with those elicited by genetically and clinically similar respiratory syncytial virus (RSV). Intense IL-6 production was evident following culture with infectious or inactivated RSV. MPV elicited IL-6 responses averaging 3.5-fold more intense (p < 0.001). Virus-dependent expression of IL-11, IL-12, IFN-alpha, and other innate immunity cytokines differed little between MPV and RSV. When examining adaptive immunity, RSV infection elicited strong IFN-gamma responses by all 60 adults. In marked contrast, MPV elicited IFN-gamma in a lower frequency of adults (p < 0.002) and at levels averaging 6-fold weaker (p < 0.001). These Th1-dominated responses were CD4, CD8, CD86 dependent, and were closely paralleled by strong virus-driven IL-10 and CCL5 production. For MPV and RSV, Th2 (IL-5, IL-13) responses were sporadic, occurring in 10-40% of the population. Thus, MPV and RSV, although both ubiquitous and leading to very high levels of infection, seroconversion, and clinically similar presentation in the population, evoke distinct innate and adaptive T cell-dependent cytokine responses. Although both viruses yield Th1-dominated responses with strong IL-10 and CCL5 production, MPV restimulation results in markedly more robust IL-6 and significantly weaker adaptive cytokine responses, in both prevalence and intensity, than does RSV.

Human metapneumovirus: a ubiquitous and long-standing respiratory pathogen

BACKGROUND

Human metapneumovirus (hMPV) is a recently described human pathogen first identified in respiratory specimens of young children suffering from respiratory syndromes ranging from mild to severe.

METHODS AND RESULTS

Virological studies have reported the presence of hMPV infections in many countries from all continents. Seroprevalence studies have indicated that the virus has been circulating in humans for more than 50 years and that it infects virtually all children by the ages of 5-10 years. In young children, hMPV has been mainly associated with bronchiolitis but also with pneumonitis, otitis media and acute exacerbation of asthma. The contribution of hMPV in respiratory syndromes of adults has been studied considerably less; initial studies have indicated a role for this pathogen in flu-like syndromes and in significant percentages of chronic obstructive pulmonary disease exacerbations and cases of community-acquired pneumonia during the winter-spring period. Both primate and rodent experimental models have been used to characterize the pathogenesis of this respiratory virus. In some of these models, intranasal hMPV inoculation has elicited not only important viral replication but also significant pulmonary inflammation and clinical disease. Recently a few groups have developed reverse genetic systems for hMPV, allowing a better understanding of viral pathogenesis and generation of attenuated viral strains for immunization.

CONCLUSIONS

Recent studies on hMPV have provided a better understanding of the epidemiology and pathogenesis associated with this viral infection, and have enhanced the prospect of developing efficient therapeutic agents and vaccine candidates.

[SARS, avian influenza, and human metapneumovirus infection]

Beginning in the 1950s respiratory viruses have been gradually discovered by isolation in cell cultures The last were the coronaviruses in the 1960s. No new respiratory viruses were discovered until 2001 when human metapneumovirus was found in respiratory specimens from children with bronchiolitis. A year later, in November 2002, severe acute respiratory syndrome (SARS) suddenly appeared as atypical pneumonia. A novel virus belonging to the Coronaviridae family was found to be a cause of this infection. In 2004, a second coronavirus was discovered (CoV-NL63) and in 2005 a third new coronavirus was described (CoV-HKU1). In addition, several subtypes of the influenza A virus, previously known to infect only poultry and wild birds, were recently found to have been directly transmitted to humans. Respiratory infection has been a considerable problem for humans for centuries. Now, in the 21st century, with new associated viruses continuously emerging, it remains an important field for work.

Human Metapneumovirus Infection in Adults with Community-Acquired Pneumonia and Exacerbation of Chronic Obstructive Pulmonary Disease

We tested nasopharyngeal aspirate specimens by real-time polymerase chain reaction assays and paired serum samples by enzyme-linked immunosorbent assays. Acute human metapneumovirus infections were identified in 6 (4.1%) of 145 adult patients who presented to the emergency department for pneumonia or acute exacerbation of chronic obstructive pulmonary disease during 2 winter/spring seasons in Quebec, Canada.