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    New serological Flow Cytometry Multiplex Assay

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    Immunostep and the Spanish National Research Council (CSIC) announced the launch of a new serological test that differentiates vaccinated individuals from those who have suffered from Covid-19 natural infection.

    The new antibody test detects three types of antibodies against four proteins of the SARS-CoV-2 virus with a single blood sample and a reliability of 99%. Unlike other tests on the market, this technology makes it possible to know which people have been infected with covid-19 through natural infection and who have developed antibodies after vaccination.

    A team of researchers from the Spanish National Research Council (CSIC), in collaboration with Immunostep laboratories in Salamanca, has developed, a new antibody test capable of identifying, quantifying and differentiating antibodies produced by covid-19 vaccination and natural infection with a specificity and sensitivity close to 100%. The main advantage of this test, based on the flow cytometry technique and developed for diagnostic use, is the detection of different antibodies against different antigens in a single tube. Furthermore, a small sample of serum or plasma provides a very complete picture of the immune response to the virus.

    The groups of CSIC researchers at the National Biotechnology Center (CNB-CSIC) and the company Immunostep have managed to identify three different types of antibodies (IgG, IgA, IgM) and four proteins of the SARS-CoV-2 virus at the same time: Spike protein and its RBD domain, two very important proteins because they are the main component of current vaccines, as well as the  nucleocapsid  protein (N) and the protease responsible for virus replication (Mpro/3CLpro).

    DIFFERENTIATING IMMUNOLOGICAL PROFILES

    Unlike most other available tests, which assess a single type of antigen, this test can differentiate between people who have been infected with covid-19 and those who have been vaccinated. “After vaccination, antibodies are only produced against the protein that the vaccine targets (which is the Spike protein and its RBD domain in most of the cases), while a person who has been infected also generates antibodies against the Mpro and NP proteins,” explains José Miguel Rodríguez Frade, a researcher at the CNB-CSIC.

    Immunostep R&D department declared that they are not aware of the existence on the international market of an equally complete test so far, with the capacity to provide a similar amount of simultaneous information on the immune response to the virus. The test arrives to complete the company’s serological solutions line by providing a technology within its speciality, flow cytometry.

    What also makes it a particularly innovative assay is that it uses this highly efficient technique, compared to most current tests based on ELISA or chromatography techniques. “Flow cytometry is the technique commonly used to obtain the percentage of white blood cells and other blood cells in routine blood tests. These instruments are available in all hospitals and clinical diagnostic laboratories.  What is new is the use of this technique for a serological assay,” says Mar Valés, an immunologist at the CNB-CSIC.

    The kit offers a lot of information with a very small sample use, which makes it a very efficient method. Its development is also compatible with all standard flow cytometry technologies that can be found in laboratories and the duration of this test is about two hours and can be automated.

    FOUR VIRAL PROTEINS AND THREE TYPES OF ANTIBODIES

    As Covid-19 is a very recent disease, there are still many unanswered questions about the type of immune response that is generated against the virus. In fact, as the pandemic has progressed, different clinical manifestations have been detected that may be associated with different intensities of the components of the immune response. “Detecting the  response to different viral proteins will help us to better understand immunity to SARS-CoV-2, which will be very useful for early classification of patients,” says Hugh Reyburn, CNB-CSIC scientist.

    The test also detects three types of antibodies, which gives an indication of the timing of the patient’s infection: IgM (immunoglobulin M), the first to be generated after infection, indicates that the individual is initiating the response to the disease; IgG (immunoglobulin G) is produced at a more advanced stage of infection and can persist over time, reporting up to months after an individual has suffered from the disease; and immunoglobulin A (IgA), which is more localised on mucosal surfaces such as the respiratory tract, although it is also detected in the patient’s serum.

    This assay is therefore an essential tool for monitoring the immune response against SARS-CoV-2 after vaccination, and for the exhaustive knowledge of the characteristics of the response in different individuals, as well as its duration over time. Although the device has been developed with patient sera, it is expected that in the future it will also be validated for use with saliva samples.