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Analysis of SARS-CoV-2 immune responses
In-depth analysis of immune responses to SARS-CoV-2 is essential for vaccine development and optimisation of immunisation strategies. A trio of new assays from EUROIMMUN for quantification of anti-S1/receptor binding domain IgG antibodies, detection of neutralising antibodies targeting S1/RBD, and analysis of specific T-cell responses supports the differentiated investigation of SARS- CoV-2-specific immune responses.
V
accination represents the most important weapon to combat the Covid-19 pandemic. According to the WHO and the London School of Hygiene and Tropical Medicine, more than 310 Covid vaccine candidates are currently in development or clinical trials, with several vaccines now approved and in use in different countries.
The main target used in Covid vaccines is the viral spike protein. The receptor binding domain (RBD) of the spike protein S1 subunit is responsible for binding to the human cellular receptor angiotensin- converting enzyme 2 (ACE2) and mediating entry of the virus into the host cells. Antibodies of class IgG against S1/RBD of the viral spike protein and specific long-lived T-cells are suspected to play the most relevant roles in virus neutralisation and sustained immunity. However, it is currently not known what concentration of antibodies confers protection against Covid-19, or how long the immune protection lasts. T-cell immunity, particularly to the spike protein, appears to be associated with strong protection, even in patients who do not exhibit detectable levels of antibodies.
Antibody quantification The WHO recently approved the first international reference material for standardisation of results from anti-SARS- CoV-2 serological assays (NIBSC code: 20/136). EUROIMMUN rapidly aligned its quantitative S1-based ELISA to this standard. The new CE-marked and fully automatable Anti-SARS-CoV-2 QuantiVac ELISA (IgG) allows quantification of antibody concentrations in standardised binding antibody units (BAU/ml), based on a six-point calibration curve. The assay is validated for serum, plasma and dried blood spots as sample material. The quantitative
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Only through assessing the strength of Covid-19 immunity will societies be able to return to some normality. T-cell analysis
determination of IgG antibodies with this ELISA provides valuable support for assessing individual immune responses to SARS-CoV-2 after infection and for evaluating the level of immune reaction achieved by spike protein-based vaccines.
Neutralising antibodies
Measurement of the neutralising activity of anti-S1/RBD antibodies enables confirmation of their functionality in inhibiting S1/RBD binding to ACE2 and thus preventing infection. The gold standard for determining neutralising antibodies is the plaque reduction neutralisation test (PRNT) or virus neutralisation test (V-NT). These tests are, however, time consuming and expensive to perform, and require biosafety level three laboratory conditions. A new CE-marked ELISA provides fast and economical determination of the inhibiting effect of anti- SARS-CoV-2 antibodies. The SARS-CoV-2 NeutraLISA is based on competitive binding between neutralising antibodies in the patient samples and labelled ACE2 receptors to recombinant S1 coated on to the microplate wells. The assay demonstrates a 98.6% agreement with the PRNT. It is suitable for routine laboratory diagnostics and can be fully automated.
Cellular immunity to SARS-CoV-2 conferred by long-lasting T-cells can be measured using the interferon gamma release assay (IGRA). Interferon gamma is an important signalling molecule of the immune system that is released by the T-cells on contact with the virus. The IGRA is performed on heparinised whole blood samples. The T-cells in the samples are stimulated based on specific viral spike protein in the provided tubes, and the interferon gamma released by the T-cells is subsequently determined using a fully automated quantitative ELISA. The IGRA is an especially useful tool for studies investigating the cellular immune response in SARS-CoV-2-infected or vaccinated individuals. The EUROIMMUN IGRA is currently available for research use only. A broad analysis of both humoral and cellular immune responses to SARS-CoV-2 is critical for evaluating the efficacy of vaccines and vaccine candidates. It also supports studies into immunological memory and cross protection between SARS-CoV-2 variants, as well as long-term epidemiological surveillance and modelling of population-level immunity. ●
www.euroimmun.com 29
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