Dengue virus envelope domain III immunization elicits predominantly cross-reactive, poorly neutralizing antibodies localized to the AB loop: implications for dengue vaccine design.

Dengue virus (DENV) is a mosquito-borne virus that causes severe health problems. An effective tetravalent dengue vaccine candidate that can provide life-long protection simultaneously against all four DENV serotypes is highly anticipated. A better understanding of the antibody response to DENV envelope protein domain III (EDIII) may offer insights into vaccine development. Here, we identified 25 DENV cross-reactive mAbs from immunization with Pichia pastoris-expressed EDIII of a single or all four serotype(s) using a prime-boost protocol, and through pepscan analysis found that 60 % of them (15/25) specifically recognized the same highly conserved linear epitope aa 309-320 of EDIII. All 15 complex-reactive mAbs exhibited significant cross-reactivity with recombinant EDIII from all DENV serotypes and also with C6/36 cells infected with DENV-1, -2, -3 and -4. However, neutralization assays indicated that the majority of these 15 mAbs were either moderately or weakly neutralizing. Through further epitope mapping by yeast surface display, two residues in the AB loop, Q316 and H317, were discovered to be critical. Three-dimensional modelling analysis suggests that this epitope is surface exposed on EDIII but less accessible on the surface of the E protein dimer and trimer, especially on the surface of the mature virion. It is concluded that EDIII as an immunogen may elicit cross-reactive mAbs toward an epitope that is not exposed on the virion surface, therefore contributing inefficiently to the mAbs neutralization potency. Therefore, the prime-boost strategy of EDIII from a single serotype or four serotypes mainly elicited a poorly neutralizing, cross-reactive antibody response to the conserved AB loop of EDIII.

Evaluation and analysis of dengue virus enhancing and neutralizing activities using simple high-throughput assays.

The risk of antibody-dependent enhancement (ADE) of dengue virus (DENV) infection is a major obstacle for the development of dengue vaccine candidates. Here, we described a novel approach for assessment of ADE by measuring DENV nonstructural protein 1 (NS1) production in culture supernatants with Fcγ receptor-expressing K562 cells in ELISA format (ELISA-ADE). Enhancing activities quantified by measurement of kinetics of NS1 production were in a good agreement with the results of the virus titration assay. In conjunction with the previously established enzyme-linked immunospot-based micro-neutralization test (ELISPOT-MNT) in 96-well format, the observable dose-response profiles of enhancing and neutralizing activities against all four DENV serotypes were produced with two flaviviral envelope cross-reactive monoclonal antibodies and four primary DENV-1-infected human sera. The simple high-throughput ELISA-ADE assay offers advantages for quantitative measurement of infection enhancement that can potentially be applied to large-scale seroepidemiological studies of DENV infection and vaccination.

[Establishment and preliminary application of dengue virus envelope domain III IgG antibody capture enzyme-linked immuno-absorbent assay].

OBJECTIVE: To establish a highly sensitive and specific assay to detect dengue virus (DENV) envelope protein domain III (EDIII) IgG antibody, and to explore its value in the diagnosis and seroepidemiological survey of dengue. METHODS: The DENV EDIII IgG antibody capture ELISA was developed using the recombinant full-length DENV EDIII, which was prepared by Pichia yeast expression system as the capture antigen. The serum samples were collected from the same group of 35 DENV-1 patients of primary infection during disease period in 2006 and their follow-up phase in 2010; and the sensitivity of the assay was compared to that of the commercial Panbio DENV IgG ELISA. RESULTS: The sensitivity of DENV EDIII IgG ELISA in detecting the serum samples from disease period and follow-up phase was 87% (20/23) and 94% (33/35), respectively; whereas the sensitivity of Panbio DENV IgG ELISA was 71% (25/35) and 0, respectively. The sensitivity of DENV EDIII IgG ELISA in detecting the serum samples from both periods was similar, without statistical significance (χ(2) = 0.946, P = 0.331). For serum samples from disease period, the sensitivity of DENV EDIII IgG ELISA was comparable with that of Panbio DENV IgG ELISA (χ(2) = 1.924, P = 0.165). However, DENV EDIII IgG ELISA demonstrated a significantly higher sensitivity than Panbio DENV IgG ELISA in detecting the serum samples from follow-up phase (χ(2) = 62.432, P = 0.000). CONCLUSION: DENV EDIII IgG capture ELISA is highly sensitive in detecting IgG in the serum samples from either disease period or follow-up phase. This method might be a promising alternative for diagnosis and seroepidemiologic survey of dengue.

Evaluation of human enterovirus 71 and coxsackievirus A16 specific immunoglobulin M antibodies for diagnosis of hand-foot-and-mouth disease.

BACKGROUND: Hand-foot-and-mouth disease (HFMD) is caused mainly by the human enterovirus type 71 (HEV71) and the Coxsackievirus A group type 16 (CVA16). Large outbreaks of disease have occurred frequently in the Asia-Pacific region. Reliable methods are needed for diagnosis of HFMD in children. IgM-capture ELISA, with its notable advantages of convenience and low cost, provides a potentially frontline assay. We aimed to evaluate the newly developed IgM-capture ELISAs for HEV71 and CVA16 in the diagnosis of HFMD, and to measure the kinetics of IgM over the course of HEV71 or CVA16 infections. RESULTS: We mapped, for the first time, the kinetics of IgM in HEV71 and CVA16 infection. HEV71- and CVA16-IgM were both detectable in some patients on day 1 of illness, and in 100% of patients by day 5 (HEV71) and day 8 (CVA16) respectively; both IgMs persisted for several weeks. The IgM detection rates were 90.2% (138 of 153 sera) and 68.0% (66 of 97 sera) for HEV71 and CVA16 infections, respectively, during the first 7 days of diseases. During the first 90 days after onset these values were 93.6% (233 of 249 sera) and 72.8% (91 of 125 sera) for HEV71 and CVA16 infections, respectively. Some cross-reactivity was observed between HEV71- and CVA16-IgM ELISAs. HEV71-IgM was positive in 38 of 122 (31.1%) CVA16 infections, 14 of 49 (28.6%) other enteroviral infections and 2 of 105 (1.9%) for other respiratory virus infected sera. Similarly, CVA16-IgM was apparently positive in 58 of 211 (27.5%) HEV71 infections, 16 of 48 (33.3%) other enterovirus infections and 3 of 105 (2.9%) other respiratory virus infected sera. Nevertheless, the ELISA yielded the higher OD450 value of main antibody than that of cross-reaction antibody, successfully identifying the enteroviral infection in 96.6% (HEV71) and 91.7% (CVA16) cases. When blood and rectal swabs were collected on the same day, the data showed that the agreement between IgM-capture ELISA and real-time RT-PCR in HEV71 was high (Kappa value = 0.729) while CVA16 somewhat lower (Kappa value = 0.300). CONCLUSIONS: HEV71- and CVA16-IgM ELISAs can be deployed successfully as a convenient and cost-effective diagnostic tool for HFMD in clinical laboratories.

Functional properties of DENV EDIII­reactive antibodies in human DENV­1­infected sera and rabbit antiserum to EDIII.

The envelope domain III (EDIII) of the dengue virus (DENV) has been confirmed to be involved in receptor binding. It is the target of specific neutralizing antibodies, and is considered to be a promising subunit dengue vaccine candidate. However, several recent studies have shown that anti­EDIII antibodies contribute little to the neutralizing or enhancing ability of human DENV­infected serum. The present study involved an analysis of the neutralization and antibody­dependent enhancement (ADE) activities of EDIII­reactive antibodies in human convalescent sera from patients with primary DENV­1 infection and rabbit antiserum immunized with recombinant DENV­1 EDIII protein. The results indicated that serum neutralization was not associated with titres of EDIII­binding antibodies in the human DENV­1­infected sera. The depletion of anti­EDIII antibodies from these serum samples revealed that the anti­EDIII antibodies of the patients contributed little to neutralization and ADE. However, the EDIII­reactive antibodies from the rabbit antiserum exhibited protective abilities of neutralization at a high dilution (~1:50,000) and ADE at a low dilution (~1:5,000) for the homotypic DENV infection. Notably, the rabbit antiserum displayed ADE activity only at a dilution of 1:40 for the heterotypic virus infection, which suggests that EDIII­reactive antibodies may be safe in secondary infection with heterotypic viruses. These results suggest that DENV EDIII is not the predominant antigen of the DENV infection process; however, purified or recombinant DENV EDIII may be used as a subunit vaccine to provoke an effective and safe antibody response.

Development of a double antibody sandwich ELISA for West Nile virus detection using monoclonal antibodies against non-structural protein 1.

The early diagnosis of West Nile virus (WNV) infection is important for successful clinical management and epidemiological control. The non-structural protein 1 (NS1) of flavivirus, a highly conserved and secreted glycoprotein, is abundant in the serum of flavivirus-infected patients and represents a useful early diagnostic marker. We developed a WNV-specific NS1 antigen-capture ELISA using two mouse monoclonal antibodies (MAbs) that recognised distinct epitopes of the NS1 protein of WNV as capture and detection antibodies. The antigen-capture ELISA displayed exclusive specificity to WNV without cross-reaction with other related members of the flavivirus family, including the dengue virus, yellow fever virus, Japanese encephalitis virus, and tick-borne encephalitis virus. Additionally, the specificity was presented as no false positive in normal (0/1003) and DENV-infected (0/107) human serum specimens. The detection limit of the antigen-capture ELISA was as low as 15 pg/ml of recombinant WNV NS1 protein (rWNV-NS1) and 6.1 plaque-forming units (PFU)/0.1 ml of WNV-infected culture supernatant. In mice infected with WNV, the NS1 protein was readily detected in serum as early as one day after WNV infection, prior to the development of clinical signs of the disease. The sensitivity of the NS1 capture ELISA (93.7%) was significantly higher (79.4%) than that of real-time reverse transcription polymerase chain reaction in 63 serum samples from WNV-infected mice (p = 0.035). This newly developed NS1 antigen-capture ELISA with high sensitivity and specificity could be used as an efficient method for the early diagnosis of WNV infection in animals or humans.

The absence of exanthema is related with death and illness severity in acute enterovirus infection.

OBJECTIVE: To clarify whether exanthema is related to illness severity in acute enterovirus infection in children. METHODS: The data of pediatric inpatients at Zhujiang Hospital during 2009-2012 with an acute enterovirus infection were reviewed retrospectively. Enterovirus infection was determined by real-time reverse transcription PCR. Clinical data were summarized and compared between cases with and without exanthema. RESULTS: A total of 780 pediatric inpatients with an acute enterovirus infection were included in this study, of whom 83 (10.6%) presented no exanthema. The percentage of deaths in the group of patients without exanthema was significantly higher than that in the group with exanthema (7.2% vs. 1.1%; p = 0.002). Central nervous system involvement (41.0% vs. 30.0%; p = 0.041), severe central nervous system (CNS) involvement (21.7% vs. 11.0%; p = 0.005), severe CNS involvement with cardiopulmonary failure (9.6% vs. 2.3%; p = 0.002), an altered level of consciousness (15.7% vs. 7.6%; p = 0.013), and convulsions (14.4% vs. 6.3%; p = 0.007) occurred significantly more frequently in the group without exanthema. CONCLUSIONS: A considerable proportion of children with an acute enterovirus infection in Guangdong Province, China during 2009-2012 presented no exanthema, and the absence of exanthema was found to be related to death and illness severity for these acute enterovirus infections. Clinicians in China should consider enterovirus as the possible pathogen when treating children with an acute pathogen infection without exanthema.

Characterization of enterovirus 71 and coxsackievirus A16 isolated in hand, foot, and mouth disease patients in Guangdong, 2010.

BACKGROUND: Hand, foot, and mouth disease (HFMD) is an acute viral disease caused by human enteroviruses, especially human enterovirus 71 (HEV71) and coxsackievirus A16 (CVA16), and mainly affects infants and young children. After the outbreak in 2008 in Fuyang, China, HFMD was classified as a category C notifiable infectious disease by the Ministry of Health of China. METHODS: In this study, we report the epidemiologic and clinical manifestations of HFMD in Guangdong Province, China in 2010, and characterize HEV71 and CVA16 isolated from clinical specimens. RESULTS: Among the 542 HFMD patients, 495 (91.3%) were positive for enterovirus as detected by real-time reverse transcriptase PCR; 243 were positive for HEV71 (49.1%, 243/495) and 114 were positive for CVA16 (23.0%, 114/495). Most of the affected children were aged 5 years or under (93.7%, 508/542). Phylogenetic analyses of VP1 gene sequences showed that the HEV71 isolates belonged to C4a subgenotype, and CVA16 isolates belonged to B1 genotype. CONCLUSIONS: Our results demonstrate that HEV71 and CVA16 are the primary causative agents responsible for HFMD in Guangdong Province, and their co-circulation poses a potential risk to public health.

Effect of simulated dynamic intraocular pressure on retinal thickness measured by optical coherence tomography after cataract surgery.

AIM: To investigate the effect of simulated dynamic intraocular pressure (SDIOP) during uncomplicated phacoemulsification on postoperative macular and peripapillary retinal nerve fiber layer (RNFL) thickness. METHODS: Macular and RNFL thicknesses in one eye of patients (n=30) undergoing uncomplicated phacoemulsification were measured by optical coherence tomography preoperatively and 1 week postoperatively. The best-corrected visual acuity, SDIOP, irrigation time (IT), effective phacoemulsification time, entire surgical duration, blood pressure, and heart rate were recorded. RESULTS: The mean SDIOP and IT was (74.9 ± 27.4)cmH(2)O and (178.4 ± 21.6) seconds respectively. We divided our patients into two groups based upon IT with greater than 90cmH(2)O (P(>90)IT). In Group A (n=14), the P(>90)IT was greater than the mean P(>90)IT, and in Group B (n=16), the P(>90)IT was less than the mean P(>90)IT. For all patients there was a significant increase in macular thickness one week after cataract surgery (P=0.001). While the RNFL thickness tended to increase, the change was not significant. The postoperative macular thickness of Group A, (277.8 ± 13.7)µm, was significantly thicker than that of Group B, (267.9 ± 15.0)µm (P=0.004). The postoperative peripapillary RNFL thickness of Group A, (96.8 ± 10.8) µm, was not significantly different from Group B. For Group A, the change in macular thickness was positively correlated with P(>90)IT (R(2)=0.524, P=0.02). There was no statistical difference in postoperative visual acuity between Groups A and B. CONCLUSION: After uncomplicated phacoemulsification, increased macular thickness is associated with the IT under high SDIOP. The effect of high SDIOP is limited to the sub-clinical level.

[Production and characterization of the monoclonal antibodies against nonstructural 1 protein of DENV-4].

AIM: To produce monoclonal antibodies (mAbs) against nonstructural 1 protein (NS1) of DENV-4 and characterization. METHODS: BALB/c mice were immunized with recombinant DENV4-NS1 protein and inactive DENV-4. Splenocytes of immunized mice were fused with myeloma cells (NS-1) to produce hybridoma cell lines, secreting anti-DENV4-NS1 protein mAbs. ELISA was used to identify the mAbs against NS1of DENV-4. Immnofluorescence assay (IFA) and Western blot analysis were applied to identify the specificity of mAbs. RESULTS: fifteen mAbs recognizing two different antigenic epitopes on NS1of DENV-4 were obtained. These mAbs had characteristics of specific binding to recombinant NS1 of DENV-4. The IFA showed that all of the mAbs strongly reacted to DENV-4, while had no cross-reactivity to the other three serotypes of dengue virus. CONCLUSION: mAbs against NS1 of DENV-4 with high specificity has been successfully established. These results lay the foundation value for study on the structural and functional of DENV4-NS1 protein and early diagnosis of DENV-4 infection.

Enzyme-linked immunosorbent assay-format tissue culture infectious dose-50 test for titrating dengue virus.

A dengue nonstructural protein 1 (NS1) antigen capture enzyme-linked immunosorbent assay (ELISA)-based tissue culture infectious dose-50 (TCID(50)) test (TCID(50)-ELISA) was developed as an alternative to the standard plaque assay for titrating dengue virus. Virus titers obtained by TCID(50)-ELISA were comparable to those obtained by the plaque assay and by the traditional TCID(50)-cytopathic effect (CPE) test (TCID(50)-CPE), with a better reproducibility and a lower coefficient of variation. Quantitative comparison of TCID(50)-ELISA and TCID(50)-CPE resulted in a correlation coefficient of 0.976. Moreover, this new method showed a wider application to C6/36, Vero E6, BHK-21, and Vero cells compared with other titration methods. In summary, the novel TCID(50)-ELISA method described here provides a more reliable and more accurate alternative compared to the plaque assay and TCID(50)-CPE for titration of dengue virus.