Secondary Dengue Virus Infection Research Articles

A modified IgG avidity assay for reliability improvement of an in-house capture ELISA to discriminate primary from secondary dengue virus infections

Although discrimination between primary and secondary dengue infections can be performed using commercially available immunoassays or in-house tests, the evaluation of these methods is important, but is often problematic due to incomplete clinical data. In many cases, patients’ sera submitted to the laboratory may not include the date of onset of illness which is necessary to discriminate primary and secondary dengue infections. This study reports improvement of an in-house capture ELISA using IgG avidity to discriminate primary and secondary dengue virus infection. Modified definition criteria were applied to characterize 99 single sera based on their IgM/IgG ratios. Regressive analysis indicated that the avidity test results (avidity index of 60 % as cutoff) for the discrimination showed good agreement (96 %) and a high correlation (r = −0.81) with those of the in-house capture ELISA (IgM/IgG ratio at 1.2 as cutoff). To further evaluate the in-house tests, 318 convalescent sera were compared with a Focus Diagnostics’ anti-dengue IgM ELISA. Compared with the Focus Diagnostics system, the sensitivity of an in-house IgM determination was 83 %, whereas using both IgM and IgG capture ELISAs the sensitivity increased to 95 %.

Public health needs and challenges in influenza and dengue vaccines–Implications from epidemiological findings

Background: The incidence and mortality rates of influenza and dengue have been high in most Asian countries. Vaccination is the one of the most important and successful public health measures in controlling many infectious diseases such as poliomyelitis, measles, and Japanese encephalitis. However, the etiological agents of these two diseases are RNA viruses involving different subtypes/serotypes with dynamic changes each year, posing greater challenges in future years. Methods and materials: Field epidemiology during outbreak periods provides the best chance in fully understanding dynamic changes of the studied virus and evaluating the impact of mismatched human influenza viruses. On the other hand, incidence and hospitalization rates, case fatality rates and seroepidemiological study of dengue are important in assessing public health needs and community effectiveness of vaccine as well as in finding target population to receive dengue vaccine. Results: We found that the higher isolation rate of seasonal influenza A (H3N2) and the circulating vaccine-mismatched human influenza viruses, the greater monthly P&I mortality in elderly, using a negative binomial model. Moreover, those years with high excess P&I mortality had the circulating virus strains with a lower amino acid identity percentages of HA1 protein with the vaccine strains. During 2009 pandemic influenza, one unique adaptive mutant at E374K of HA2 in A (H1N1/09) viruses evolved through the epidemic, emerged as a dominant strain at post-peak period, extended in areas with high population densities before mass immunization, persisted till ten months post-nationwide vaccination, and were finally fixed as herd immunity developed. Recently, different tetravalent dengue vaccines providing immunity against all four serotypes of dengue virus (DENV) have been developed to avoid antibody-dependent enhancement (ADE) from secondary DENV infection. The initial clinical trials in many cities of dengue-endemic countries did reduce the incidence and hospitalization rates of dengue. Conclusion: Weekly monitoring excess P&I mortality and evaluating laboratory-confirmed human influenza cases with/without receiving flu vaccines plus serological tests on antigenic variation can assure public health effectiveness of influenza vaccines. Once novel influenza virus emerges with worldwide spread, virological surveillance in high population-density areas can assess the virus with high epidemic potential. Furthermore, more immuno-epidemiological studies are needed for dengue in different settings.

Secondary dengue virus infection in communities with preexisting multiple heterotypic dengue virus antibodies: A longitudinal study in Malaysia

Secondary dengue virus infection in communities with preexisting multiple heterotypic dengue virus antibodies: A longitudinal study in Malaysia

Chimeric flavivirus enables evaluation of antibodies against dengue virus envelope protein in vitro and in vivo

In a secondary dengue virus (DENV) infection, the presence of non-neutralizing antibodies (Abs), developed during a previous infection with a different DENV serotype, is thought to worsen clinical outcomes by enhancing viral production. This phenomenon is called antibody-dependent enhancement (ADE) of infection, and it has delayed the development of therapeutic Abs and vaccines against DENV, as they must be evaluated for the potential to induce ADE. Unfortunately, limited replication of DENV clinical isolates in vitro and in experimental animals hinders this evaluation process. We have, therefore, constructed a recombinant chimeric flavivirus (DV2ChimV), which carries premembrane (prM) and envelope (E) genes of type 2 DENV (DENV-2) R05-624 clinical (Thai) isolate in a backbone of Japanese encephalitis virus (Nakayama strain). DENV E-protein is the most important viral target, not only for neutralizing Abs, but also for infection-enhancing Abs. In contrast to DENV-2 R05-624, DV2ChimV replicated efficiently in cultured mammalian cells and was lethal in interferon-α/β–γ-receptor double-knockout mice. With DV2ChimV, we were able to perform neutralization assays, in vitro and in vivo ADE assays, and in vivo protection assays. These results suggest that the chimeric virus is a powerful tool for evaluation of Abs against DENV.

Major Histocompatibility Complex Class I Chain-Related A and B (MICA and MICB) Gene, Allele, and Haplotype Associations With Dengue Infections in Ethnic Thais.

Major histocompatibility complex class I chain-related (MIC) A and B (MICA and MICB) are polymorphic stress molecules recognized by natural killer cells. This study was performed to analyze MIC gene profiles in hospitalized Thai children with acute dengue illness. MIC allele profiles were determined in a discovery cohort of patients with dengue fever or dengue hemorrhagic fever (DHF) (n = 166) and controls (n = 149). A replication cohort of patients with dengue (n = 222) was used to confirm specific MICB associations with disease. MICA*045 and MICB*004 associated with susceptibility to DHF in secondary dengue virus (DENV) infections (odds ratio [OR], 3.22; [95% confidence interval (CI), 1.18-8.84] and 1.99 [1.07-2.13], respectively), and MICB*002 with protection from DHF in secondary DENV infections (OR, 0.41; 95% CI, .21-.68). The protective effect of MICB*002 against secondary DHF was confirmed in the replication cohort (OR, 0.43; 95% CI, .22-.82) and was stronger when MICB*002 is present in individuals also carrying HLA-B*18, B*40, and B*44 alleles which form the B44 supertype of functionally related alleles (0.29, 95% CI, .14-.60). Given that MICB*002 is a low expresser of soluble proteins, these data indicate that surface expression of MICB*002 with B44 supertype alleles on DENV-infected cells confer a protective advantage in controlling DENV infection using natural killer cells.

Incidence Dengue Virus Infection in Children with Acute Fever in Endemic Area, Lesson from Primary Health Care in Western Java Indonesia

Context: In endemic countries, most of dengue fever cases clinically resembles other diseases or just flu-like syndrome, it is important to detect dengue infection in patient with acute fever 1 to 4 day and which serotype of dengue virus that circulation to determine the risk of severe case of dengue to occur in primary health care. Aims: The aim of this study was to identify the incidence of dengue viral infection among children with acute fever in endemic area, and which serotype of dengue virus that circulating in community in Bandung, West Java, Indonesia. Settings and Design: Prospective cohort analysis study. Methods and Material: patients age 0 to 18 years old with acute fever from Sukajadi, Neglasari, and Padasuka Primary Health Centre form march to October 2018. These primary health centers represent three subdistricts with high dengue case every year in Bandung. Inclusion criteria: Fever at least 37.6oC, 1-4 days, with or not taking antipyretics. Name, age, and sex, nutritional status, and laboratorium examination that has been done by primary health centre was collect. Rapid NS1 antigen test is done as an additional check, multiplex real time RT-PCR assay for dengue virus (1-4) was perform from blood sample that NS1 antigen positive. Statistical analysis used: independent t-test analysis. Results: A total of 178 blood samples from patients with acute fever collected. 40 (22,5%) samples were positive with rapid NS1 antigen test, mean body temperature significantly higher in confirmed dengue virus cases (37,66 (±2,07) vs 38,33 (±0,83); p0,005) and platelet count (239.218 (±99.402) vs 164.739,13 (±98.259); p>0,005) is lower in confirmed dengue virus cases. From 40 positive NS1 antigen test, 17 (42,5%) showed all serotype (Den 1-4) of dengue can be found, with 8 (47,05%) is Den 3. Conclusions: Incidence of dengue cases in patient with acute febrile in endemic urban area is quite high, and all serotype of dengue virus can be found, so the risk of secondary dengue virus infection is imminent.

Clinical, Virological, and Cytokine Profiles of Children Infected with Dengue Virus during the Outbreak in Southern Vietnam in 2017.

Dengue virus (DENV) infection is a major cause of morbidity and mortality in Vietnam, and the incidence is higher and more consistent in the southern part of the country. This study investigated the circulation of DENV serotypes, viremia levels, immunological status, and cytokine levels, with disease severities among children infected in 2017 in Ho Chi Minh City, Southern Vietnam. Acute and convalescent serum samples were collected from clinically diagnosed dengue children. They were confirmed to have DENV infection by NS1 antigen, IgM and IgG ELISAs, virus isolation, and conventional and real-time RT-PCR. Measurement of 10 cytokine levels was performed in the serum samples. All the children were dengue IgM positive; 28% and 72% of them had primary and secondary DENV infections, respectively, whereas 54% of those with secondary infection were children with dengue with warning signs and with severe dengue. Any or mixed infection of the four serotypes of DENV RNA was detected in 58 children. Twenty DENV strains (DENV-1 = 16 and DENV-4 = 4) were isolated. Levels of IFN-γ, TNF-α, MCP-1, IL-10, and IL-6 were significantly higher in severe dengue cases. We report the predominance of DENV-1 over other serotypes in the 2017 dengue outbreak in Southern Vietnam. Our data showed that cytokine expressions were correlated with dengue pathogenesis and may help in identifying an effective therapeutic strategy.

A (class-)switch in the antibody response may distinguish primary from secondary dengue virus infection.

A (class-)switch in the antibody response may distinguish primary from secondary dengue virus infection.

When Can One Vaccinate with a Live Vaccine after Wild-Type Dengue Infection?

Recommendations have been issued for vaccinating with the Sanofi Pasteur tetravalent dengue vaccine (CYD-TDV, Dengvaxia®) individuals aged from 9 to 45/60 years old with a prior dengue virus (DENV) infection and living in endemic countries/areas. One question linked to these recommendations is to determine when it is possible to start vaccination after laboratory confirmed wild-type DENV infection, and this question can be relevant to any live vaccine to be used in endemic areas. To address it, we reviewed and discussed the immunological and practical considerations of live vaccination in this context. Firstly, the nature and kinetics of immune responses triggered by primary or secondary DENV infection may positively or negatively impact subsequent live vaccine take and associated clinical benefit, depending on when vaccination is performed after infection. Secondly, regarding practical aspects, the “easiest” situation would correspond to a confirmed acute dengue fever, only requiring knowing when the patient should come back for vaccination. However, in most cases, it will not be possible to firmly establish the actual date of infection and vaccination may have to take place during well-defined periods, regardless of when prior infection occurred. Evidence that informs health authorities and medical practitioners in formulating vaccine policies and implementing vaccine programs is thus needed. The present work reviewed the different elements of the guidance and proposes some key conclusions and recommendations.

Phenotype and functionality of follicular helper T cells in patients with acute dengue infection

BackgroundThe association of functionality and phenotype of follicular helper T cells (Tfh) with dengue virus (DENV) specific antibody responses and clinical disease severity has not been well studied.MethodsWe investigated the phenotype and functionality of Tfh cells and plasmablasts in adult patients (DF = 18, DHF = 22) with acute dengue (day 4 to 8 since onset of fever) of varying severity using multiparametric flowcytometry. The properties of Tfh cells were correlated with viraemia, disease severity, plasmablast responses and DENV-specific serum antibody responses. We further evaluated the kinetics of neutralizing antibodies (Neut50) throughout the course of illness in order to evaluate their association with clinical disease severity and viraemia.ResultsTfh cells (especially those producing IL-21 and co-expressing PD-1 and ICOS) were found to be significantly expanded (p < 0.0001) and highly activated in patients with DHF compared to those with DF. The frequency of Tfh cells significantly correlated with DENV-specific IgG, NS1-specific antibodies and Neut50 antibody titres in patients with DHF but not in those with DF. Although the Neut50 titres increased during the course of acute secondary DENV infection, they showed differences based on serotype. For instance, the Neut50 titres were significantly higher during the latter part of illness in patients with DF compared to DHF in DENV1 infection, while in DENV2, patients with DHF had significantly higher titres. The viral loads during early illness did not correlate with the subsequent rise in the Neut50 antibody titres during any time point of illness.ConclusionsThe expansion of Tfh cells is associated with DHF and DENV-specific IgG, NS1-specific and neutralizing antibodies. Neut50 titres did not associate with disease severity or viraemia at the point of first presentation during the febrile phase, but later titres do show differential association with severity in patients with DENV1 compared to DENV2.

A STUDY TO DETERMINE THE INCREASING DENGUE INCIDENCE IN BIHAR REGION: AN OBSERVATIONAL STUDY.

Introduction: Dengue is one of the most serious mosquitos borne viral infection mainly affecting tropical and subtropical countries of the world. In absence of specific treatment and vaccine for dengue fever (DF); vector control is the only method by which spread of dengue can be prevented. The present study was conducted to determine the increasing dengue incidence in Bihar region.&#x0D; Material and Method: This study was done to report the sero prevalence of Dengue virus infection at Bihar, North India. The laboratory records of clinically suspected Dengue patients from jan 2018 to Nov 2018 were analyzed retrospectively for demographic features, seasonal variations, and results of IgM and IgG anti dengue antibodies tested by Dengue IGM capture enzyme linked immune sorbent assay (MAC ELISA).&#x0D; Results: A total of 1035 serum samples were analyzed. Out of which 209 samples (20.19%) were found positive for dengue virus infection. Maximum positive cases were seen in 2019 (53.11%). Seasonal trend showed that infection started appearing in august, peaked in October and slowly tapered by December.&#x0D; Conclusion: The most affected age group was 11 to 15 years of age, (57.3%) followed by 6 to10 year’s group (27.3 %)and least effective age group was 0 to 5 year (15.4%), majority of cases were found to be of secondary dengue virus infection (93.8%). Male to female ratio was 2:1.The present outbreak thus emphasizes the need for continuous sero epidemiological surveillance for the timely formulation and implementation of effective dengue control programme.&#x0D; Keywords: Dengue, dengue haemorrhagic fever, IgM antibody capture enzyme linked immune sorbent assay (MAC ELISA), India, vector.

Primary and Secondary Dengue Virus Infections Elicit Similar Memory B-Cell Responses, but Breadth to Other Serotypes and Cross-Reactivity to Zika Virus Is Higher in Secondary Dengue.

The 4 antigenically distinct serotypes of dengue virus (DENV) share extensive homology with each other and with the closely related Zika flavivirus (ZIKV). The development of polyclonal memory B cells (MBCs) to the 4 DENV serotypes and ZIKV during DENV infection is not fully understood. In this study, we analyzed polyclonal MBCs at the single-cell level from peripheral blood mononuclear cells collected ~2 weeks or 6-7 months postprimary or postsecondary DENV infection from a pediatric hospital-based study in Nicaragua using a Multi-Color FluoroSpot assay. Dengue virus elicits robust type-specific and cross-reactive MBC responses after primary and secondary DENV infection, with a significantly higher cross-reactive response in both. Reactivity to the infecting serotype dominated the total MBC response. Although the frequency and proportion of type-specific and cross-reactive MBCs were comparable between primary and secondary DENV infections, within the cross-reactive response, the breadth of MBC responses against different serotypes was greater after secondary DENV infection. Dengue virus infection also induced cross-reactive MBC responses recognizing ZIKV, particularly after secondary DENV infection. Overall, our study sheds light on the polyclonal MBC response to DENV and ZIKV in naive and DENV-preimmune subjects, with important implications for natural infections and vaccine development.

CD27 &lt;sup&gt;hi&lt;/sup&gt;CD38 &lt;sup&gt;hi&lt;/sup&gt;&amp;nbsp;Plasmablasts are Activated B Cells of Mixed Origin with Distinct Function

Clinically important broadly reactive B cells evolve during multiple infections. The phenotype and function of B cells re-activated during secondary infection is different compared to B cells activated after a primary infection. Here we studied CD27high CD38high plasmablasts from patients with a primary or secondary dengue virus infection. Three transcriptionally and functionally distinct plasmablast clusters were identified. The largest cluster 0/1 was plasma cell-related and contained cells coding for virus serotype cross-reactive antibodies of the IgG1 isotype, consistent with memory B cell activation during an extrafollicular response. In contrast, cells in clusters 2 and 3 expressed low levels of antibody genes and high levels of genes associated with oxidative phosphorylation, EIF2 pathway and mitochondrial dysfunction. Clusters 2 and 3 also showed a transcriptional footprint of T cell help, in line with activation from either naive B cells or memory B cells in the context of a germinal center reaction.

Enzyme-linked immunosorbent assays using virus-like particles containing mutations of conserved residues on envelope protein can distinguish three flavivirus infections

ABSTRACT The recent outbreaks of Zika virus (ZIKV) in flavivirus-endemic regions highlight the need for sensitive and specific serological tests. Previously we and others reported key fusion loop (FL) residues and/or BC loop (BCL) residues on dengue virus (DENV) envelope protein recognized by flavivirus cross-reactive human monoclonal antibodies and polyclonal sera. To improve ZIKV serodiagnosis, we employed wild type (WT) and FL or FL/BCL mutant virus-like particles (VLP) of ZIKV, DENV1 and West Nile virus (WNV) in enzyme linked immunosorbent assays (ELISA), and tested convalescent-phase serum or plasma samples from reverse-transcription PCR-confirmed cases with different ZIKV, DENV and WNV infections. For IgG ELISA, ZIKV WT-VLP had a sensitivity of 100% and specificity of 52.9%, which was improved to 83.3% by FL/BCL mutant VLP and 92.2% by the ratio of relative optical density of mutant to WT VLP. Similarly, DENV1 and WNV WT-VLP had a sensitivity/specificity of 100%/70.0% and 100%/56.3%, respectively; the specificity was improved to 93.3% and 83.0% by FL mutant VLP. For IgM ELISA, ZIKV, DENV1 and WNV WT-VLP had a specificity of 96.4%, 92.3% and 91.4%, respectively, for primary infection; the specificity was improved to 93.7–99.3% by FL or FL/BCL mutant VLP. An algorithm based on a combination of mutant and WT-VLP IgG ELISA is proposed to discriminate primary ZIKV, DENV and WNV infections as well as secondary DENV and ZIKV infection with previous DENV infections; this could be a powerful tool to better understand the seroprevalence and pathogenesis of ZIKV in regions where multiple flaviviruses co-circulate.

Modulated Zika virus NS1 conjugate offers advantages for accurate detection of Zika virus specific antibody in double antigen binding and Ig capture enzyme immunoassays.

The accurate diagnosis and seroprevalence investigations of Zika virus (ZKV) infections remain complex due to cross reactivity with other flaviviruses. Two assay formats, both using labelled Zika virus NS1 antigen as a revealing agent (a double antigen binding assay, DABA, and an immunoglobulin Ig capture assay, G capture) were initially developed and compared with the indirect EuroimmunZ assay for the detection of anti-Zika antibody. Of 147 pre-Zika period serum samples, 39 (27%) were reactive in the EuroimmunZ or the DABA assays, 28 sera concordantly so. Such false reactivity was influenced by the serotype of Dengue virus (DV) to which individuals had been exposed to. Thus, of sera from patients undergoing secondary Dengue virus infection of known serotype, 91%, 45% and 28% of Dengue virus serotype 2, 3 and 4 respectively were reactive in one or more of the three assays. A novel method of quenching false sero-reactivity was therefore developed for the DABA and G capture assays. Initial addition of a single homologous Dengue virus serotype 3 NS1Ag quench significantly ablated false reactivities in the pre-Zika period sera. An equipotent quadrivalent quench comprising homologous Dengue virus serotypes 1 to 4 NS1Ag was shown to be optimum yet retained sensitivity for the detection of specific anti-Zika antibody. Comparing DABA and G capture assays using quenched and unquenched conjugates in comparison with EuroimmunZ early in the course of PCR-confirmed infection indicated that a significant component of the apparent early anti-ZIKA antibody response is likely to be due to a Zika virus-driven anamnestic anti-Dengue virus response. The increased specificity provided by homologous antigen quenching is likely to provide a significant improvement in sero-diagnostics and to be of clinical value.

Longitudinal Analysis of Memory B and T Cell Responses to Dengue Virus in a 5-Year Prospective Cohort Study in Thailand.

Prior exposure to dengue virus (DENV) has a profound impact on the outcome of infection, which varies according to the interval between infections. Antibodies secreted by B cells and cytokines secreted by T cells are thought to contribute both to protective immunity against DENV and the pathogenesis of dengue disease. We analyzed peripheral blood mononuclear cells (PBMC) collected from Thai children over a 5-year prospective cohort study to define the dynamics of DENV-specific memory B and T cell responses and the impact of symptomatic or subclinical DENV infections. To measure B cell responses, PBMC were stimulated with IL-2 plus R848 and culture supernatants were tested for DENV-binding antibodies by ELISA. To measure T cell responses, PBMC were stimulated in dual-color ELISPOT assays with overlapping peptide pools of structural and non-structural proteins from the four DENV types. B cell responses were low to one or more DENV types prior to symptomatic infection and increased with reactivity to all four types after infection. Subjects who had a subclinical infection or who did not experience a DENV infection during the study period showed strong memory B cell responses to all four DENV types. T cell responses to DENV peptides demonstrated a cytokine hierarchy of IFN-γ > IL-2 > IFN-γ/IL-2. T cell responses were low or absent prior to secondary infections. The trends in T cell responses to DENV peptides over 3 year post-infection were highly variable, but subjects who had experienced a secondary DENV1 infection showed higher cytokine responses compared to subjects who had experienced a secondary DENV2 or subclinical infection. The longitudinal nature of our study demonstrates persistent memory B cell responses over years and a lasting but variable impact of secondary DENV infection on DENV-specific T cell responses.

Performance of InBios ZIKV Detect™ 2.0 IgM Capture ELISA in two reference laboratories compared to the original ZIKV Detect™ IgM Capture ELISA

ZIKV Detect™ 2.0 IgM Capture ELISA (InBios International, Seattle, WA) recently replaced the ZIKV Detect™ IgM Capture ELISA and a number of significant changes have been made to the original version. This study compares data generated from the ZIKV Detect™ 2.0 IgM Capture ELISA, to data generated using the original version of the kit. The same sample sets were used in this comparison, and reference test results for these samples were used to assess sensitivity, specificity, accuracy and concordance of results across two laboratories. Average sensitivity increased from 90.4% to 92.5% with the updated kit where the increase was not statistically different, and specificity increased from 79.5% to 97.4%, a statistically-significant difference. Accuracy of the ZIKV Detect™ 2.0 IgM Capture ELISA was 89% compared to 63.9% for the original version of the kit, and agreement across the laboratories increased from 79.5% to 97.4%. With secondary dengue virus infections, specificity increased from 9.3% to 82.6% with the updated kit, primarily due to the change in interpretation criteria that no longer includes “Possible Zika positive.”

Accuracy of the SD BIOLINE Dengue Duo for rapid point-of-care diagnosis of dengue.

BackgroundRapid diagnosis tests (RDTs) are easy to carry out, provide fast results, and could potentially guide medical treatment decisions. We investigated the performance of a commercially available RDT, which simultaneously detects the non-structural 1 (NS1) dengue virus (DENV) antigen, and IgM and IgG DENV antibodies, using representative serum samples from individuals in a dengue endemic area in Salvador, Brazil.Methodology/Principal findingsWe evaluated the accuracy of the SD BIOLINE Dengue Duo RDT (Abbott, Santa Clara, USA; former Alere Inc, Waltham, USA) in a random collection of sera. Samples included acute-phase sera from 246 laboratory-confirmed dengue cases and 108 non-dengue febrile patients enrolled in a surveillance study for dengue detection, 73 healthy controls living in the same surveillance community, and 73 blood donors. RDT accuracy was blindly assessed based on the combined results for the NS1 and the IgM test components. The RDT sensitivity was 46.8% (38.6% for the NS1 component and 13.8% for the IgM component). Sensitivity was greater for samples obtained from patients with secondary DENV infections (49.8%) compared to primary infections (31.1%) (P: 0.02) and was also influenced by the result in the confirmatory dengue diagnostic test, ranging from 39.7% for samples of cases confirmed by IgM-ELISA seroconversion between paired samples to 90.4% for samples of cases confirmed by a positive NS1-ELISA. The RDT specificity was 94.4% for non-dengue febrile patients, 87.7% for the community healthy controls, and 95.9% for the blood donors.Conclusions/SignificanceThe SD BIOLINE Dengue Duo RDT showed good specificities, but low sensitivity, suggesting that it may be more useful to rule in than to rule out a dengue diagnosis in dengue endemic regions.

NK Cells Activated through Antibody-Dependent Cell Cytotoxicity and Armed with Degranulation/IFN-\u03b3 Production Suppress Antibody-dependent Enhancement of Dengue Viral Infection

Antibody (Ab)-dependent enhancement (ADE) is a hypothesized mechanism of increased disease severity during secondary dengue virus (DENV) infection. This study investigates Ab-dependent cell cytotoxicity (ADCC) in counteracting ADE. In our system, DENV and DENV-immune sera were added to peripheral blood mononuclear cells (PBMCs), and ADE and NK cell activation were simultaneously monitored. ADE was detected in monocytes and a concurrent activation of NK cells was observed. Activated NK cells expressed IFN-γ and CD107a. IFN-γ was detected at 24 hours (24 h) followed by a rapid decline; CD107a expression peaked at 48 h and persisted for >7 days. Optimal activation of NK cells required the presence of enhancement serum together with ADE-affected monocytes and soluble factors, suggesting the coexistence of the counteractive ADCC Abs, in the same ADE-serum, capable of strongly promoting NK cell activation. The function of NK cells against ADE was demonstrated using a depletion assay. NK cell-depleted PBMCs had increased ADE as compared to whole PBMCs. Conversely, adding activated NK cells back into the NK-depleted-PBMCs or to purified monocytes decreased ADE. Blocking IFN-γ expression also increased ADE. The study suggests that under ADE conditions, NK cells can be activated by ADCC Abs and can control the magnitude of ADE.

Adaptive immune responses to primary and secondary dengue virus infections.

Dengue is the leading mosquito-borne viral illness infecting humans. Owing to the circulation of multiple serotypes, global expansion of the disease and recent gains in vaccination coverage, pre-existing immunity to dengue virus is abundant in the human population, and secondary dengue infections are common. Here, we contrast the mechanisms initiating andsustaining adaptive immune responses during primary infection with the immune pathwaysthat are pre-existing and reactivated during secondary dengue. We also discuss newdevelopments in our understanding of the contributions of CD4+ T cells, CD8+ T cells and antibodies to immunity and memory recall. Memory recall may lead to protective or pathological outcomes, and understanding of these processes will be key to developing or refining dengue vaccines to be safeand effective.