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The Introduction of Dengue Virus

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Firstly, let us see two antibodies:

  1. 4G2 antibody

This product is a mouse monoclonal antibody that specifically recognizes E protein from DENV-2. The E protein-binding antibody 4G2 is an epitope-specific antibody that can be used in ELISA.

  1. A11 antibody

Recombinant Human Antibody (EDE2 A11) is capable of binding to DENV E proteins, expressed in HEK 293 cells as the combination of a heavy chain (HC) containing VH from anti-DENV E proteins mAb and CH1-3 region of human IgG1 and a light chain (LC) encoding VL from anti-DENV E proteins mAb and CL of human kappa light chain.

So, what is DENV?

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Figure1. Dengue virus

Dengue virus (DENV) belongs to a serotype subgroup of flaviviridae. Its morphological structure is similar to that of Japanese encephalitis virus (JEV), but its size is small, about 17-25 nm. It can be divided into four serotypes according to antigenicity, 1, 2, 3 and 4 serotypes. There are antigenic differences among different viral strains in the same type.

Viral characteristics and physicochemical properties

DENV has a capsule and is a single positive strand RNA virus without segments. The viral genome is about 11 KB long. It encodes three structural proteins (C-prM-E) and seven non-structural proteins (NS1-NS2A-NS2B-NS3-NS4A-NS4B-NS5). Among them, E protein is the main structural protein of the virus, which determines the histophilicity of the virus and mediates the binding of the virus to cell receptors. At the same time, it is also an important component of influencing virulence, causing protective immune response and immunopathological damage. The virus is sensitive to heat and can be inactivated at 56 ℃ for 30 minutes. Lipid solvents such as chloroform, acetone, lipase or sodium deoxycholate can inactivate the virus by destroying its envelope. Viruses are sensitive to gastric acid, bile and protease, and to ultraviolet and gamma rays.

Antigenicity and serotype

According to the antigenicity of virus E protein, it can be divided into four serotypes: DENV1, DENV2, DENV3 and DENV4. The antigenicity of these viruses was cross-linked, but not with other antigens of flaviviridae. Antigenic determinants of viral envelope protein E can induce protective neutralizing antibodies and hemagglutination inhibitory antibodies, and may be involved in the occurrence of dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS). NS1 and NS3 are both immunoreactive and immunogenic, which can induce protective immunity against dengue virus homology in mice.

Clinical symptoms

Dengue virus often causes asymptomatic recessive infection. The main clinical manifestations of the patients are dengue fever (DF), dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS). The main clinical manifestations of DF include protruding fever, severe headache (mostly frontal pain), post-ocular pain (aggravation of eyeball movement), general pain and joint pain, nausea and vomiting, lymphadenopathy, leukopenia and thrombocytopenia. DF not only causes heart, liver, lung, kidney, brain and other system damage, but also leads to myocardial damage. The clinical manifestations of DHF/DSS are more serious. In addition to the above DF symptoms, severe and persistent abdominal pain, nasal, oral and gingival bleeding, skin bleeding and ecchymosis, black stool, extreme thirst, pale skin and mucosa, chills, restlessness or sleepiness, hematocrit > 35% and other manifestations can occur. Serious cases can cause death. DENV infection can also cause encephalitis.

Pathogenesis

The pathogenesis of dengue fever and dengue haemorrhagic fever has not been fully elucidated so far. It is generally believed that the complex interaction between virus and host causes severe risk factors, including patient's age, virus serotype and genotype, and host's genetic background. Recent studies have shown that there are several hypotheses about the pathogenesis: viral affinity, viral toxicology, host susceptibility, antibody-dependent enhancement (ADE), cross-reactive T cell response and cytokine storm. This paper briefly introduces ADE and cytokine storm.

Scholars believe that there are group-specific determinants and type-specific determinants on the surface of DENV. The antibodies produced by the former have a strong enhancement effect on DENV infection, called enhanced antibodies, while the antibodies produced by the latter are called neutralizing antibodies. When the body is re-infected with different types of DENV, serum neutralizing antibodies cannot completely neutralize the virus. Enhanced antibodies can bind with the virus to form immune complexes. These immune complexes promote the replication of the virus in these cells through Fc receptors on the membrane of monocytes or macrophages, resulting in ADE effect, leading to clinical outcomes in patients. Symptoms worsen, blood concentration and shock occur, resulting in DHF/DSS. However, DHF/DSS can also occur in many patients with primary infection, indicating that there are other pathogenic factors.

Cytokines are small molecular weight soluble proteins or polypeptides secreted by immune cells and other types of cells. They have the functions of transmitting information between cells, regulating immune response, and participating in inflammatory damage and other pathological processes. However, excessive inflammation can cause systemic inflammatory response syndrome and make the body in a state of hypermetabolism and hyperdynamic circulation. Over-release of inflammatory cytokines may lead to multiple organ dysfunction syndrome and even death. The control of inflammation is essential in the treatment of many diseases. It was found that the levels of IL-1, IL-4, IL-6, IL-13 and TNF-alpha were significantly increased in severe patients with dengue fever. There is a significant correlation between TNF-alpha and thrombocytopenia. Studies have shown that the transition from Th1-type response to Th2-type response is an important mechanism of DHF/DSS. Cytokines in severe patients are mostly Th2-type cytokines. After virus infection, excessive release of cytokines and inflammatory factors increases vascular permeability, leading to hemorrhage and shock.

Diagnosis

The diagnosis of dengue virus is mainly a combination of clinical symptoms and laboratory diagnosis. Laboratory diagnosis of dengue virus includes virus isolation, antigen and antibody detection, gene detection and so on.

  1. Virus isolation

Virus isolation is the golden standard for the diagnosis of viral diseases. The duration of dengue viremia is relatively short. Samples should be collected within 4 to 5 days of the onset of fever. Virus isolation and culture can be carried out by living mosquitoes, cells or animals.

  1. Antigen detection

NS1 protein is the main marker antigen of dengue virus infection. NS1 protein appears earlier than IgM antibody and can be used for early diagnosis. At present, several commercial kits have been used to detect the NS1 antigen of dengue virus.

  1. Serological detection

The serological method is more convenient because the humoral immune response of patients infected with dengue virus lasts for at least several weeks after the onset of the disease and the sample can be collected for a relatively long time. Detection of IgM, IgG capture ELISA, IgM, IgG indirect ELISA and hemagglutination inhibition test are the most commonly used serological methods for diagnosis of dengue virus infection.

  1. Gene diagnosis

In recent years, the molecular biology diagnostic methods of dengue virus have been enhanced. Nucleic acid amplification has become the most important method for rapid diagnosis of dengue virus. Various RT-PCR methods try to detect the RNA of dengue virus. The nucleic acid amplification technique can be used to identify the serotype of dengue virus as well as to detect the virus.

Owing to its high throughput and parallel processing, gene chip technology can detect and analyze pathogens comprehensively. Its simple and fast operation, low cost and small size provide wide application prospects in the fields of molecular biology, disease diagnosis and treatment. Scientists used PCR to amplify the nearly full-length dengue virus 2 gene, digested the amplified products by enzyme-digestion-PCR, and constructed the dengue virus 2 DNA library to obtain microarray probes. The probe was fabricated into a DNA chip for detection of type 2 dengue virus by dot analyzer. The results showed that the hybridization of the sample with type 2 dengue virus gene chip was highly sensitive and specific.

Dengue fever, as an important vector-borne infectious disease, has been increasing year by year, seriously endangering human health. Although some achievements have been made in the related research, there are still many problems to be solved urgently. There is still no consensus on the pathogenesis of dengue fever, especially in severe cases. There is no effective prevention and treatment measures. Future work should start with the mechanism of virus and host, obtain effective treatment of dengue fever as soon as possible, and todevelop a protective multivalent vaccine.


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