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Antibodies test for Covid-19 with near 100% accuracy

A new serological test for Covid-19 with an accuracy close to 100% has been developed by researchers from the CSIC, in collaboration with the hospitals of La Princesa and La Paz. The Spanish biotechnology company Immunostep produces and commercializes the test.

The test is based on proteins of the virus that had not been previously used for diagnosis and that generate a strong production of antibodies

The test detects three types of antibodies and enables the identification of people who have been in contact with the coronavirus and have developed immunity. It is a useful tool to design an efficient vaccination strategy for the population, as it allows to differentiate people that have generated a response to the vaccine from people that have been infected by the virus.

The test is an ELISA kit with all the reagents to perform analysis in laboratories. Outcome measure is obtained in two hours. It has been patented through the Deputy Vice-presidency for Knowledge Transfer of the CSIC and has been licensed to the company Immunostep.

"The main novelty of the test is that it is based on viral proteins that had not been previously studied to be used in diagnosis," explains Mar Valés, researcher at the National Center for Biotechnology of the CSIC (CNB-CSIC), who has co-led the research work.

A protein to capture antibodies

"We found that protease, a protein that the virus makes during infection, can act as an antigen. Patients generate antibodies that can be detected in blood samples," she adds. CNB-CSIC researcher Hugh Reyburn has led the works to obtain the protease that is used to capture antibodies against the coronavirus in patient’s blood samples. A colour change indicates the result.

The scientists have tested the Elisa kit in a study published in the Journal of Immunology. The results showed that the new assay, in combination with other antigens, enables finding out if someone has developed immunity against the coronavirus. The other antigens have been obtained also at the CNB-CSIC by Hugh Reyburn and José María Casanovas teams.

"The test is extremely sensitive, and the combination of a new antigen with the IgG and IgA immunoglobulins allows the detection of antibodies practically from the onset of symptoms," says Ricardo Jara, CEO of Immunostep. “Given its high sensitivity, we believe it will be a very powerful tool at this stage of vaccination that we have started now,” he adds.

"This test allows a broader study of the immune response of antibodies to viruses, "says Eduardo López, coordinator of the immunology department at the Hospital Universitario de La Paz in Madrid". It is possible to see the response to antibodies against more proteins than the ones usually included in many tests, including the finding of the CSIC group, the protease, which generates antibody response," he adds. "That's why we believe this test is more versatile than others that are already available."

Qualitative and quantitative detection

There are two major types of diagnostic kits, depending on whether they make a direct or indirect detection. While PCR tests detect virus genetic material and antigen tests detect virus surface proteins (direct detection), antibody tests detect proteins generated by the immune system in response to coronavirus infection (indirect detection).

This new test not only detects the presence or absence of three types of antibodies but also their concentration. "The new test identifies three types of antibodies, called immunoglobulins: IgM, or immunoglobulin M, is the first to be generated after infection, usually five or six days after the onset of symptoms. It is a sign that the body is beginning to respond to the disease and the patient therefore can still be contagious. The second antibody, the IgG or immunoglobulin G, occurs at a later stage and lasts for several weeks or months, so it is useful to know if somebody has suffered the infection in the past. The third antibody, IgA or immunoglobulin A, appears when the virus is in the mucous membranes, "said researcher José Miguel Rodríguez Frade, of the CNB-CSIC, who co-directed the work.