Heterologous Serotypes Research Articles

Dengue Virus Infection: Immune Response and Therapeutic Targets

Flavivirus infection, especially dengue virus infection caused by DENV, is known to be a significant health concern globally owing to the high incidence and mortality rate. The expanding and increasing disease burden calls for the need to develop an effective treatment and prevent the event of fatal complications, including dengue hemorrhagic fever/dengue shock syndrome. The DENV-induced immune response has been described as paradoxical because it has a protective role in viral clearance but, at the same time, causes more severe infection through viral-specific immunity. This is further complicated by high homology and cross-reactivity between different serotypes of DENV, causing a more severe disease presentation during secondary infection by a heterologous serotype. This serotype complexity poses a challenge for the development of a universal flavivirus vaccine. This review highlights the significance of high motility group box 1 (HMGB1) and nucleotide-binding oligomerization domain, leucine rich repeat and pyrin domain containing 3 (NLRP3) inflammasome activation pathways in initiating an inflammatory response through the downstream activation of nuclear factor κB and proinflammatory cytokine Interleukin (IL)-1B, IL-18 release in DENV infection. It also discusses the role of NLRP3 in activating cellular apoptosis and pyroptosis leading to systemic failure, especially in peripheral tissues. Over the decades, there has been much progress in understanding the immunopathogenesis of DENV infection. Researchers have been studying key pathogenic molecules for potential therapeutic targets including HMGB1 and NLRP3 inflammasome inhibitors, which is explored in this review. Ultimately, although there is not yet an effective antiviral or vaccine for DENV, immunomodulators continue to pave the way to decrease disease severity in infected individuals.

Impact of Different Foot and Mouth Disease Vaccine Schemes in Cross-Neutralization Against Heterologous Serotype O Strains in Cattle

The high antigenic variability of the foot-and-mouth disease virus (FMDV) represents a challenge for developing prophylactic strategies, stressing the need for research into vaccines offering broad protection against a range of virus strains. Here, the heterotypic cross-reaction using different vaccine schemes against serotype O strains was studied, evaluating the impact of revaccination, antigen dose, and incorporation of additional FMDV serotypes. Naïve cattle were immunized with seven distinct FMDV vaccines, receiving three doses of the same formulation at 0, 28, and 56 days post-primary vaccination (dpv). Serum samples were collected up to 70 dpv and tested by a virus-neutralizing test against serotype O strains from a South American lineage and two strains representative of two Asian lineages. Our results showed that vaccines containing the ME-SA topotype O1/Campos strain developed cross-neutralizing responses against the two Asian viruses after the first vaccination. In contrast, significant heterotypic neutralizing antibody titers against the homologous topotype strain were only found after the second vaccination, indicating that the phylogenic relationship may differ from the antigenic profiles for these two viruses. The amount of the O1/Campos strain and the revaccination were essential factors for neutralization against the homologous- and heterologous-type O FMDV viruses. The strain composition of the vaccine was only relevant for cross-neutralization against one of the Asian strains, suggesting potential intra-serotypic divergences for this pattern.

B cell receptor dependent enhancement of dengue virus infection.

Dengue virus (DENV) is the causative agent of dengue, a mosquito-borne disease that represents a significant and growing public health burden around the world. A unique pathophysiological feature of dengue is immune-mediated enhancement, wherein preexisting immunity elicited by a primary infection can enhance the severity of a subsequent infection by a heterologous DENV serotype. A leading mechanistic explanation for this phenomenon is antibody dependent enhancement (ADE), where sub-neutralizing concentrations of DENV-specific IgG antibodies facilitate entry of DENV into FcγR expressing cells such as monocytes, macrophages, and dendritic cells. Accordingly, this model posits that phagocytic mononuclear cells are the primary reservoir of DENV. However, analysis of samples from individuals experiencing acute DENV infection reveals that B cells are the largest reservoir of infected circulating cells, representing a disconnect in our understanding of immune-mediated DENV tropism. In this study, we demonstrate that the expression of a DENV-specific B cell receptor (BCR) renders cells highly susceptible to DENV infection, with the infection-enhancing activity of the membrane-restricted BCR correlating with the ADE potential of the IgG version of the antibody. In addition, we observed that the frequency of DENV-infectible B cells increases in previously flavivirus-naïve volunteers after a primary DENV infection. These findings suggest that BCR-dependent infection of B cells is a novel mechanism immune-mediated enhancement of DENV-infection.

Maternally Derived Antibodies to Foot-and-Mouth Disease Virus Modulate the Antigenic Specificity of Humoral Responses in Vaccinated Cattle.

Vaccination is widely used to control foot-and-mouth disease (FMD), but maternal antibodies may interfere with the response to vaccination in calves. This study, conducted on a regularly vaccinated Malaysian dairy farm, aimed to optimise the vaccination regime by measuring the in vitro neutralising virus antibody responses of 51 calves before and after vaccination with a one or two dose vaccination regime starting at 2-7 months old. The presence of maternal antibodies was associated with poor post-vaccination antibody responses after a single dose of vaccine in calves less than 6 months old. However, a second dose of vaccine given three weeks later, improved the antibody responses in all ages of calves. This confirms the view that in regularly vaccinated farms, some combination of delay and revaccination is needed to achieve effective immunization of calves. Sera from cows and pre-vaccinated calves neutralised homologous serotype A vaccine virus more strongly than a heterologous serotype A field virus, but this pattern was reversed in some calves after vaccination. The strength of heterologous responses in calves 49 days after first vaccination correlated to the amount of transferred maternal antibody, suggesting that pre-existing antibodies could have modulated the specificity of these active antibody responses. If confirmed, such an effect by pre-existing antibodies could have wider implications for broadening the coverage of FMD vaccine responses.

Influence of previous Zika virus infection on acute dengue episode.

The co-circulation of flaviviruses in tropical regions has led to the hypothesis that immunity generated by a previous dengue infection could promote severe disease outcomes in subsequent infections by heterologous serotypes. This study investigated the influence of antibodies generated by previous Zika infection on the clinical outcomes of dengue infection. We enrolled 1,043 laboratory confirmed dengue patients and investigated their prior infection to Zika or dengue. Severe forms of dengue disease were more frequent in patients with previous Zika infection, but not in those previously exposed to dengue. Our findings suggest that previous Zika infection may represent a risk factor for subsequent severe dengue disease, but we did not find evidence of antibody-dependent enhancement (higher viral titer or pro-inflammatory cytokine overexpression) contributing to exacerbation of the subsequent dengue infection.

The L-DBF vaccine cross protects mice against different Shigella serotypes after prior exposure to the pathogen.

Shigellosis (bacillary dysentery) is a severe diarrheal disease caused by members of the genus Shigella, which results in 90 million cases annually around the world. The Shigella type III secretion system (T3SS) is a specialized secretion system that is the primary virulence factor it uses to infect the colonic mucosa. The type III secretion apparatus (T3SA) proteins IpaB and IpaD, as well as the genetic fusion, DBF, have been demonstrated to protect mice from Shigella spp. infection in a lethal pulmonary model. In a previous study, we fused LTA1, the active moiety of lethal toxin from enterotoxigenic Escherichia coli to DBF to produce a self-adjuvanting vaccine candidate L-DBF, which cross-protected mice against four serotypes of Shigella flexneri and Shigella sonnei. Here, we exposed mice with one or two sublethal doses of S. flexneri 2a to identify whether the immune response induced by L-DBF in the host would be affected by prior infection by homologous or heterologous Shigella serotypes. We demonstrate that pre-infection with two sublethal doses of S. flexneri 2a did not elicit cross-protection against S. sonnei, while vaccination with L-DBF did. Our results indicate that L-DBF is a feasible vaccine candidate that offers cross-protection against Shigella's different serotypes even after prior exposure to the pathogen. This work provides a proof of concept that a novel subunit vaccine can not only protect a naïve host from Shigella challenge, but also can protect against challenge after prior infection by the same or different Shigella serotypes. IMPORTANCE Shigellosis is endemic to low- and middle-income regions of the world where children are especially vulnerable. In many cases, there are pre-existing antibodies in the local population and the effect of prior exposure should be considered in the development and testing of vaccines against Shigella infection. Our study shows that L-DBF-induced immune responses are not adversely affected by prior exposure to this pathogen. Moreover, somewhat different cytokine profiles were observed in the lungs of vaccinated mice not having been exposed to Shigella, suggesting that the immune responses elicited by Shigella infection and L-DBF vaccination follow different pathways.

The disruption of LPS in Salmonella Typhimurium provides partial protection against Salmonella Choleraesuis as a live attenuated vaccine

Interference with the normal synthesis of LPS was shown to enhance immune responses to conserved outer membrane proteins. In the present study, we have constructed three vaccine candidates by deleting four genes (rfaL, rfbB, rffG and wzy) associated with LPS synthesis in the wild-type strain UK-1. Virulence assessment showed that after oral immunization of BALB/c mice, all mutant strains were attenuated and had significantly reduced ability to colonize host tissues compared to the wild-type strain. In addition, all three vaccine candidates induced elevated humoral, mucosal and cellular immune responses against S. Typhimurium and S. Choleraesuis OMPs compared to the PBS-treated group. Finally, immunization of mice with the rSC0136 vaccine candidate strain provided 100 % and 40 % protection against S. Typhimurium and S. Choleraesuis challenge, respectively. These results suggest that the deletion of LPS synthesis-related genes may be an effective strategy against homologous serotypes, but provides only partial protection against heterologous serotypes.

DENV-specific IgA contributes protective and non-pathologic function during antibody-dependent enhancement of DENV infection.

Dengue represents a growing public health burden worldwide, accounting for approximately 100 million symptomatic cases and tens of thousands of fatalities yearly. Prior infection with one serotype of dengue virus (DENV) is the greatest known risk factor for severe disease upon secondary infection with a heterologous serotype, a risk which increases as serotypes co-circulate in endemic regions. This disease risk is thought to be mediated by IgG-isotype antibodies raised during a primary infection, which poorly neutralize heterologous DENV serotypes and instead opsonize virions for uptake by FcγR-bearing cells. This antibody-dependent enhancement (ADE) of infection leads to a larger proportion of susceptible cells infected, higher viremia and greater immunopathology. We have previously characterized the induction of a serum IgA response, along with the typical IgM and IgG responses, during dengue infection, and have shown that DENV-reactive IgA can neutralize DENV and competitively antagonize IgG-mediated ADE. Here, we evaluate the potential for IgA itself to cause ADE. We show that IgG, but not IgA, mediated ADE of infection in cells expressing both FcαR and FcγRs. IgG-mediated ADE stimulated significantly higher pro-inflammatory cytokine production by primary human macrophages, while IgA did not affect, or slightly suppressed, this production. Mechanistically, we show that DENV/IgG immune complexes bind susceptible cells significantly more efficiently than DENV/IgA complexes or virus alone. Finally, we show that over the course of primary dengue infection, the expression of FcγRI (CD64) increases during the period of acute viremia, while FcγRIIa (CD32) and FcαR (CD89) expression decreases, thereby further limiting the ability of IgA to facilitate ADE in the presence of DENV. Overall, these data illustrate the distinct protective role of IgA during ADE of dengue infection and highlight the potential therapeutic and prognostic value of DENV-specific IgA.

Continued dominance of dengue virus serotype 2 during the recent Central India outbreaks (2019-2021) with evidence of genetic divergence

ABSTRACT Central India faced major dengue outbreaks in 2019 and 2021. In the present study, we aimed to identify the dengue virus serotypes and genotypes circulating in Central India during the COVID pre-pandemic year (2019) and ongoing-pandemic year (2021). For this purpose, the suspected cases were first tested by serological assays. Sero-positive samples were then subjected to molecular diagnosis by RT-PCR and semi-nested PCR. The serotypes obtained were confirmed by nucleotide sequencing. A phylogenetic analysis of serotypes was performed to identify the circulating genotypes. All four DENV serotypes were detected during 2019 and 2021, with the predominance of DENV2. Cases with multiple DENV serotype infections were also identified, involving DENV-2 in all the coinfections. Genotyping revealed that DENV-1 (Genotype V, American/African), DENV-2 (Genotype IV, Cosmopolitan), DENV-3 (Genotype III, Cosmopolitan), and DENV-4 (Genotype I) were involved during both outbreaks. DENV-2 detected in 2019 and 2021 has diverged from the previous strains detected in Central India (2016 and 2018), which may account for the higher transmission of DENV-2 during these outbreaks. The detection of heterologous DENV serotypes with high transmission efficiency calls for continuous viral monitoring and surveillance, which will contribute to a better understanding of changing viral dynamics and transmission patterns.

A story of Shigella vaccine development in ICMR-NICED involving multidimensional approaches

Enteric bacterial infection causes diarrhea throughout the world, especially in developing countries. Shigella is solely answerable toalmost 1.1 million deaths annually in the pediatric population. Vaccine development against diarrheal diseases is always an encouragedconcern. Our laboratory, dedicated to find a possible therapy against shigellosis, is working on a path of various potential methodologiesand immunogens. Over the years, we have concentrated and reported different immunogens with their advantages and drawbacks,ultimately leading us to find the best possible vaccine candidate against bloody diarrhea.The venture started with live attenuated vaccines that protect against multiple serotypes and subtypes of pathogens and found limitedhost-serotype specific immune responses. It was observed that introducing a lipopolysaccharide biosynthesis gene pPR 1347 in Shigelladysenteriae type 1, transformed it into an avirulent organism for candidate vaccine.A mutant strain of Shigella flexneri 2a lacking the RNA-binding protein Hfq was made, leading to increased expression of the type IIIsecretion system via loss of regulation, resulting in attenuation of cell viability through repression of stress response sigma factors. Suchincreased antigen production and simultaneous attenuation were expected to elicit protective immunity against homologous and alimited number of heterologous serotypes subtypes.Although we formulated the live attenuated vaccine through the introduction of a lipopolysaccharide gene and a mutant lackingRNA binding protein Hfq, but due to lack of heterologous protective efficacy, these were not an ideal vaccine candidate to be madeavailable in the market although they showed a significant amount of immunogenicity. Moreover, live attenuated strains always havea possibility to revert back to its virulent form.Subsequently, monovalent and hexavalent heat-killed immunogens with single and six Shigella serotypes have shown significantprotective efficacy in mice, and rabbit models. Recently we have shown the homologous as well some extent of heterologus protectiveefficacy of heat killed multi-serotype Shigella (HKMS) immunogens in a guinea pig colitis model.A novel formulation for improved immunogen delivery system comprises substantially effective amounts of alginate chitosannanoparticles with OmpA protein of Shigella species. Alginate chitosan nano formulations of OmpA consists essentially of OmpAprotein as conserved active molecule, but efficacy study reveals partial protection efficacy against present circulating Shigella. Furtherimproving the delivery system, we have also formulated a subunit-based vaccine by nanoformulation of ipaC protein of Shigella. Themain drawback of OmpA and ipaC subunit based vaccines are they cannot provide a broad spectrum protection against 50 subtypesand serotypes of Shigella, although they act as a conserved protein in Enterobacteriaceae family, indicating single epitope cannot bethe sole factor associated with the operational protective efficacy.Eventually, our research moved a step ahead and found next-generation outer membrane vesicles (OMVs) based antigens from Shigella.Disruption of tolA, one of the genes of the Tol–Pal system of Shigella membrane, has increased the OMVs release rate by approximately80% higher. Recently we have reported only four serotype-subtype cross-protection among 50 subtypes of circulating Shigella in micemodels. Outer membrane vesicles based immunogen could be a potential cost-effective non-living, next-generation candidate vaccineagainst shigellosis for humans.

Molecular Characterization and Phylogenetic Analysis of Dengue Fever Viruses in Three Outbreaks in Tanzania Between 2017 and 2019.

Dengue is a disease of public health interest, and Tanzania experienced major outbreaks in 2014 and 2019. Here, we report our findings on the molecular characterization of dengue viruses (DENV) that circulated during two smaller outbreaks (2017 and 2018) and one major epidemic (2019) in Tanzania. We tested archived serum samples from 1,381 suspected dengue fever patients, with a median age of 29 (IQR:22-40) years, referred to the National Public Health Laboratory for confirmation of DENV infection. DENV serotypes were identified by reverse transcription polymerase chain reaction (RT-PCR), and specific genotypes were identified by sequencing the envelope glycoprotein gene and phylogenetic inference methods. DENV was confirmed in 823 (59.6%) cases. More than half (54.7%) of patients with dengue fever infection were males, and nearly three-quarters (73%) of the infected individuals were living in Kinondoni district, Dar es Salaam. DENV-3 Genotype III caused the two smaller outbreaks in 2017 and 2018, while DENV-1 Genotype V caused the 2019 epidemic. DENV-1 Genotype I was also detected in one patient in 2019. This study has demonstrated the molecular diversity of dengue viruses circulating in Tanzania. We found that contemporary circulating serotypes did not cause the major epidemic of 2019 but rather due to a serotype shift from DENV-3 (2017/2018) to DENV-1 in 2019. Such a change increases the risk for patients previously infected with a particular serotype to develop severe symptoms upon potential re-infection with a heterologous serotype due to antibody-dependent enhancement of infection. Therefore, the circulation of serotypes emphasizes the need to strengthen the country's dengue surveillance system for better management of patients, early detection of outbreaks, and vaccine development.

Increased Clinical Signs and Mortality in IFNAR(-/-) Mice Immunised with the Bluetongue Virus Outer-Capsid Proteins VP2 or VP5, after Challenge with an Attenuated Heterologous Serotype.

Bluetongue is an economically important disease of domesticated and wild ruminants caused by bluetongue virus (BTV). There are at least 36 different serotypes of BTV (the identity of which is determined by its outer-capsid protein VP2), most of which are transmitted by Culicoides biting midges. IFNAR(-/-) mice immunised with plant-expressed outer-capsid protein VP2 (rVP2) of BTV serotypes -1, -4 or -8, or the smaller outer-capsid protein rVP5 of BTV-10, or mock-immunised with PBS, were subsequently challenged with virulent strains of BTV-4 or BTV-8, or with an attenuated clone of BTV-1 (BTV-1RGC7). The mice that had received rVP2 generated a protective immune response against the homologous BTV serotype, reducing viraemia (as detected by qRT-PCR), the severity of clinical signs and mortality levels. No cross-serotype protection was observed after challenge with the heterologous BTV serotypes. However, the severity of clinical signs, viraemia and fatality levels after challenge with the attenuated strain of BTV-1 were all increased in mice immunised with rVP2 of BTV-4 and BTV-8, or with rVP5 of BTV10. The possibility is discussed that non-neutralising antibodies, reflecting serological relationships between the outer-capsid proteins of these different BTV serotypes, could lead to 'antibody-dependent enhancement of infection' (ADE). Such interactions could affect the epidemiology and emergence of different BTV strains in the field and would therefore be relevant to the design and implementation of vaccination campaigns.

Trial Evaluation of Protection and Immunogenicity of Piscine Bivalent Streptococcal Vaccine: From the Lab to the Farms.

Streptococcosis is one of the major diseases that causes devastation to farmed fish, leading to significant economic losses all around the world. Currently, two serotypes of Streptococcus agalactiae, serotype Ia and III, have been identified as virulent strains and major causative agents of the disease in farmed Nile tilapia (Oreochromis niloticus Linn.) in Thailand. Upon inactivated vaccine development, monovalent inactivated whole-cell vaccines demonstrated high specific antibody production against homologous serotypes and limited production with heterologous serotypes. However, for higher efficacy, a bivalent streptococcal vaccine was designed to maximize protective immunity to both serotypes. Interestingly, our bivalent vaccine could successfully induce specific antibody production against both serotypes with similar levels, and the response could extend over the 8 weeks of the experimental period. Evaluation of vaccines in the laboratory scale revealed relative percent survival (RPS) of vaccinated tilapia to serotype Ia (81.2 ± 9.4%) and serotype III (72.2 ± 4.8%), respectively. The efficacy of the bivalent vaccine showed significant RPS higher than the monovalent vaccine (p < 0.05) at 30 days, and the protection of all those vaccines was reduced thereafter. Evaluation of the vaccine in a farm trial in different locations in Thailand revealed the efficacy of the bivalent vaccine in increasing the production yield by greater than 80% in all tested farms in 2015 and 2021. Taken together, this study affirms the efficacy of the bivalent streptococcal vaccine in the prevention of streptococcus disease in Nile tilapia, which could be used in different areas. This vaccine development could be effectively applied in the tilapia culture industry.

Capsule type defines the capability of Klebsiella pneumoniae in evading Kupffer cell capture in the liver.

Polysaccharide capsule is the main virulence factor of K. pneumoniae, a major pathogen of bloodstream infections in humans. While more than 80 capsular serotypes have been identified in K. pneumoniae, only several serotypes are frequently identified in invasive infections. It is documented that the capsule enhances bacterial resistance to phagocytosis, antimicrobial peptides and complement deposition under in vitro conditions. However, the precise role of the capsule in the process of K. pneumoniae bloodstream infections remains to be elucidated. Here we show that the capsule promotes K. pneumoniae survival in the bloodstream by protecting bacteria from being captured by liver resident macrophage Kupffer cells (KCs). Our real-time in vivo imaging revealed that blood-borne acapsular K. pneumoniae mutant is rapidly captured and killed by KCs in the liver sinusoids of mice, whereas, to various extents, encapsulated strains bypass the anti-bacterial machinery in a serotype-dependent manner. Using capsule switched strains, we show that certain high-virulence (HV) capsular serotypes completely block KC's capture, whereas the low-virulence (LV) counterparts confer partial protection against KC's capture. Moreover, KC's capture of the LV K. pneumoniae could be in vivo neutralized by free capsular polysaccharides of homologous but not heterologous serotypes, indicating that KCs specifically recognize the LV capsules. Finally, immunization with inactivated K. pneumoniae enables KCs to capture the HV K. pneumoniae. Together, our findings have uncovered that KCs are the major target cells of K. pneumoniae capsule to promote bacterial survival and virulence, which can be reversed by vaccination.

Cross-Serotype Reactivity of ELISAs Used to Detect Antibodies to the Structural Proteins of Foot-and-Mouth Disease Virus.

Antibodies to the foot-and-mouth disease virus (FMDV) capsid induced by infection or vaccination can provide serotype-specific protection and be measured using virus neutralization tests and viral structural-protein (SP-)ELISAs. Separate tests are needed for each serotype, but cross-serotype reactions complicate serotyping. In this study, inter-serotypic responses were quantified for five SP-ELISA formats by testing 294 monovalent mainly bovine sera collected following infection, vaccination, or vaccination and infection with one of five serotypes of FMDV. Over half of the samples, representing all three immunization categories, scored positive for at least one heterologous serotype and some scored positive for all serotypes tested. A comparative approach to identifying the strongest reaction amongst serotypes O, A and Asia 1 improved the accuracy of serotyping to 73–100% depending on the serotype and test system, but this method will be undermined where animals have been infected and/or vaccinated with multiple FMDV serotypes. Preliminary studies with stabilized recombinant capsid antigens of serotypes O and A that do not expose internal epitopes showed reduced cross-reactivity, supporting the hypothesis that capsid integrity can affect the serotype-specificity of the SP-ELISAs. The residual cross-reactivity associated with capsid surface epitopes was consistent with the evidence of cross-serotype virus neutralization.

A live-attenuated mutant CVB3 vaccine virus protects against multiple coxsackievirus B infections

Abstract Group B Coxsackieviruses (CVB) contains six serotypes, namely CVB1 through CVB6, affecting various organs. But, no vaccines are currently available to prevent these infections. We recently derived a live attenuated vaccine virus termed mutant (Mt) 10 encoding a single amino acid substitution H790A within the viral protein 1 (VP1) of the CVB3 viral canyon region. This virus could prevent myocarditis and pancreatitis caused by both homologous (CVB3) and heterologous (CVB4) serotypes in A/J mice. Mechanistically, we noted that the vaccine virus induces cross-reactive neutralizing antibodies that skewed towards mainly IgG isotypes. Similarly, by using major histocompatibility complex class II dextramers and tetramers for various VP1 epitopes, we demonstrated that the vaccine recipients develop antigen-specific T cell responses producing preferentially interferon-γ responses. Furthermore, our preliminary studies revealed that the vaccine virus could prevent the progression of diabetes-induced by CVB4 in the non-obese diabetic mice. Together, our data suggest that the Mt10 vaccine can prevent infections caused by multiple CVB serotypes, paving the way for developing monovalent CVB vaccines to prevent heart and pancreatic diseases of enteroviral origin. This work was supported by The Transformational Grant from the American Heart Association (18TPA34170206)

Modeling Dengue Immune Responses Mediated by Antibodies: Insights on the Biological Parameters to Describe Dengue Infections

Dengue fever is a viral mosquito-borne disease, a significant global health concern, with more than one third of the world population at risk of acquiring the disease. Caused by 4 antigenically distinct but related virus serotypes, named DENV-1, DENV-2, DENV-3, and DENV-4, infection by one serotype confers lifelong immunity to that serotype and a short period of temporary cross immunity to other related serotypes. Severe dengue is epidemiologically associated with a secondary infection caused by a heterologous serotype via the so-called antibody-dependent enhancement (ADE), an immunological process enhancing a new infection. Within-host dengue modeling is restricted to a small number of studies so far. With many open questions, the understanding of immunopathogenesis of severe disease during recurrent infections is important to evaluate the impact of newly licensed vaccines. In this paper, we revisit the modeling framework proposed by Sebayang et al. and perform a detailed sensitivity analysis of the well-known biological parameters and its possible combinations to understand the existing data sets. Using numerical simulations, we investigate features of viral replication, antibody production, and infection clearance over time for three possible scenarios: primary infection, secondary infection caused by homologous serotype, and secondary infection caused by heterologous serotype. Besides, describing well the infection dynamics as reported in the immunology literature, our results provide information on parameter combinations to best describe the differences on the immunological dynamics of secondary infections with homologous and heterologous viruses. The results presented here will be used as baseline to investigate a more complex within-host dengue model.

Seroepidemiologic study on convalescent sera from dengue fever patients in Jinghong, Yunnan.

After dengue virus (DENV) infection, antibody-dependent enhancement (ADE) is easy to occur when the neutralizing antibody (NAb) gradually decreases to a sub-neutralizing concentration. In this cohort surveillance, we utilized sera samples collected from dengue fever patients at different convalescent phases in Jinghong City, to investigate the dynamic change rule of DENV-specific antibodies, and to analyze the risk of ADE caused by secondary infection with heterologous serotypes DENVs. For baseline serosurvey, 191 four-year and 99 six-year sera samples during convalescence were collected in 2017 and 2019, respectively. The positive rate of DENV-specific immunoglobulin G was 98.4% in 2017, which significantly decreased to 82.8% in 2019. The geometric mean titer (GMT) of NAb decreased from 1:155.35 to 1:46.66. Among 290 overall samples, 73 paired consecutive samples were used for follow-up serosurvey. In four-year sera, the GMTs of NAb against DENV-3 and cross-reactive antibodies against DENV-1, DENV-2 and DENV-4 were 1:167.70, 1:13.80, 1:18.54 and 1:45.26, respectively, which decreased to 1:53.18, 1:10.30, 1:14.60 and 1:8.17 in six-year sera. In age-stratified analysis, due to the increasing number of ADE positive samples from 2017 to 2019 in 31–40 and 51–60 years groups, the risk of ADE in DENV-4 infection was positively associated with the extension of convalescent phase, and the odd ratio was higher than other groups. With the recovery period lengthened, the risk of secondary infection with DENV-1 and DENV-2 was reduced. Our results offer essential experimental data for risk prediction of severe dengue in hyper-endemic dengue areas, and provide crucial scientific insight for the development of effective dengue vaccines.

Dengue Shock Syndrome: Its Similarity with Anaphylaxis and with the Homeopathic Medicine Apis mellifica (European Honeybee).

Dengue, with four viral serotypes, causes epidemics in tropical and sub-tropical regions. Allopathic antiviral therapies and a vaccine of general use are lacking. The homeopathic medicine Apis mellifica, advised in anaphylaxis from honeybee sting, is proposed to address the life-threatening dengue shock syndrome, which develops from dengue hemorrhagic fever and has features of anaphylaxis. In both dengue and anaphylaxis, immunoglobulin E activates, and released vasoactive mediators (importantly histamine, tryptase and platelet-activating factor) cause, a vascular permeability enabling shock. In dengue, another mechanism, namely antibody-dependent enhancement, due to secondary infection with a heterologous dengue serotype, is associated with release of vasoactive mediators. The homeopathic medicine Apis mellifica indicates plasma leak, shock, and the serous effusion that is noted in dengue patients, and is a suggested prophylactic and therapeutic medicine for dengue shock syndrome.

Development and Characterization of a Multiplex Assay to Quantify Complement-Fixing Antibodies against Dengue Virus.

Antibodies capable of activating the complement system (CS) when bound with antigen are referred to as “complement-fixing antibodies” and are involved in protection against Flaviviruses. A complement-fixing antibody test has been used in the past to measure the ability of dengue virus (DENV)-specific serum antibodies to activate the CS. As originally developed, the test is time-consuming, cumbersome, and has limited sensitivity for DENV diagnosis. Here, we developed and characterized a novel multiplex anti-DENV complement-fixing assay based on the Luminex platform to quantitate serum antibodies against all four serotypes (DENV1-4) that activate the CS based on their ability to fix the complement component 1q (C1q). The assay demonstrated good reproducibility and showed equivalent performance to a DENV microneutralization assay that has been used to determine DENV serostatus. In non-human primates, antibodies produced in response to primary DENV1-4 infection induced C1q fixation on homologous and heterologous serotypes. Inter-serotype cross-reactivity was associated with homology of the envelope protein. Interestingly, the antibodies produced following vaccination against Zika virus fixed C1q on DENV. The anti-DENV complement fixing antibody assay represents an alternative approach to determine the quality of functional antibodies produced following DENV natural infection or vaccination and a biomarker for dengue serostatus, while providing insights about immunological cross-reactivity among different Flaviviruses.