Advanced tools for influenza virus immunodetection and vaccine development

Influenza (also known as flu) is an acute respiratory illness caused by the influenza viruses A, B, C, and D. Among them, influenza A, B, and C can affect humans (Table 1). Influenza A and B viruses can cause epidemic (seasonal or interpandemic) influenza, and influenza A viruses can also cause pandemics.

Influenza virus structure

Influenza A viruses contain eight negative-sense, single-stranded viral RNA (vRNA) gene segments encoding 10 viral proteins (Figure 1). The eight genome segments are loosely encapsulated by the nucleoprotein (NP). Polymerase complexes, which consist of three polymerase proteins, PB1, PB2, and PA, are located at the ends of nucleocapsids. These helical capsids are encircled by the matrix protein 1 (M1) and a host-derived lipid bilayer envelope in which the viral surface glycoprotein hemagglutinin (HA) and neuraminidase (NA) and the matrix protein 2 (M2) are embedded.

HA, NA, and NP are three major antigens of the influenza virus, which play essential roles in the lifecycle of a virus (Table 2). Their recombinant proteins are widely used in basic research, therapeutics, vaccine development, and diagnosis.

Influenza pandemics and strains

Historically, influenza pandemics were caused by influenza A viruses, which can be further divided into different subtypes depending on HA and NA differences. Four influenza pandemics occurred in the past 100 years: the H1N1 Spanish flu pandemic (1918–1920), the H2N2 Asian influenza pandemic (1957–1958), the H3N2 Hong Kong flu pandemic (1968–1969), and the H1N1/09 swine flu pandemic (2009–2010) (Table 3).

The strains responsible for the four pandemics, H1N1 (Spanish flu and swine flu), H2N2 (Asian flu), and H3N2 (Hong Kong flu), have attracted widespread attention. In the last 20 years, multiple potential pandemic strains have emerged with several zoonotic influenza events (Figure 2).

Sino Biological has developed a panel of antigen proteins and antibodies for influenza pandemic strains (Table 4) designated to be used for various biochemical assays, such as the antibody titer, antigen detection, and antigenic characterisation assays.

Flu prevention and control

Early diagnosis and vaccination are important ways to prevent and control flu. Early diagnosis and treatment can effectively shorten the illness duration, relieve symptoms, and control the virus spread. The World Health Organization (WHO) recommends annual vaccination to prevent seasonal influenza.

Immunodetection

Immunodetection is a common method to diagnose flu. Antibodies targeting NP proteins are commonly used for immunodetection in different assays, including enzyme-linked immunosorbent assay, lateral flow assay, and direct fluorescent antibody tests. Due to the high frequency of antigenic drift or shift in various influenza strains, broad-spectrum influenza antibodies are particularly desired to diagnose flu.

Sino Biological has identified six pan-antibody pairs each against the NP protein of influenza A and B (Table 5). These matched pairs can detect broad-spectrum strains within the target subtype without any cross-reactivity with other subtypes (Figure 3).

Vaccine development

Flu, especially seasonal flu, is a global threat to human health. Vaccination is the most effective way to prevent the spread of infection. Each year, several different flu strains are selected as vaccine strains based on the surveillance data of the recent isolates and their performance in the previous season. In recent decades, most vaccines are trivalent or quadrivalent, including one H1N1, one H3N2, and Yamagata and/or Victoria-type flu B.

Sino Biological has released a panel of recombinant antigen products covering all WHO-recommended vaccine strains in recent years (Table 6). These products include HA, NA, and NP and are designed for vaccine development.

Summary

Despite the ongoing coronavirus disease 2019 pandemic, influenza continues to occur each year, resulting in substantial morbidity and mortality. Many relevant studies are underway to help control the influenza virus. The advanced tools developed by Sino Biological contain a large collection of recombinant virus proteins and a library of antiviral antibodies. These reagents can be widely used for immunodetection and vaccine development for the influenza virus.