COVID-19, SARS-CoV-2, Neutralizing Antibodies

SARS-CoV-2 Neutralizing Antibodies (nAbs)

Blocking Viral Binding to Cell Surface Receptor

In December 2019, a novel coronavirus, known as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), emerged in Wuhan, China, and caused the coronavirus disease 2019 (COVID-19) pandemic. Several diagnostic tests are available to detect active SARS-CoV-2 infection, including molecular diagnostic and viral antigen tests. In addition, serological assays are available that detect antibodies to SARS-CoV-2 viral antigens in individuals with an active or prior infection who developed an adaptive immune response.

Upon recognizing a virus, B cells produce and secrete antibodies, which bind to viral antigens with high specificity and affinity, resulting in several effector functions. Both IgM and IgG antibody isotypes are produced during the primary immune response, with IgM being the first to appear, followed by the production of adaptive, high-affinity IgG antibodies. A subset of antibodies can directly block virus infection by neutralization, known as neutralizing antibodies (nAbs). SARS-CoV-2 neutralizing antibodies can interfere with viral entry into host cells by blocking viral binding to a cell surface receptor. Antibodies that bind to a virus but are not neutralizing are known as binding or non-neutralizing antibodies. Although binding antibodies may flag a virus for immune cell processing and destruction, nAbs are critical for the protection and treatment of viral diseases. 

In SARS-CoV-2 infection, the spike (S) protein mediates viral attachment, fusion, and entry into host cells1. Specifically, the receptor-binding domain (RBD) of the S protein binds to the angiotensin-converting enzyme 2 (ACE2) receptor on host cells2,3. Anti-RBD neutralizing antibodies are present in the sera of convalescent COVID-19 patients4, and the RBD is considered a major immunogenic component of SARS-COV-2.

Leinco Technologies ELISA-Based Serology Assays

Leinco develops two ELISA-based serological antibody test kits for the detection of antibodies against the SARS-CoV-2 RBD. The COVID-19 Trace IgG MICRO ELISA kit allows for the qualitative detection of total anti-RBD IgG antibodies. To differentiate between binding and neutralizing antibodies, we offer the COVID-19 ImmunoRank Neutralization MICRO-ELISA kit. Unlike conventional neutralizing tests, which use live SARS-CoV-2 virus, our assay uses purified RBD and ACE2 to mimic the virus-host interactions and is well-correlated with the live virus neutralization test.

The value of ImmunoRank™ – a High Throughput Neutralizing Antibody Test

Although serological antibody tests are not suitable to detect an acute infection, they have many research applications. These include epidemiological studies, determining the quality and longevity of the natural immune response, and measuring vaccine efficacy. Our antibody kits can also identify recovered COVID-19 patients with potent neutralizing antibodies against the RBD, allowing further downstream analysis of the antibodies, including structural studies to define the epitopes recognized by these antibodies. A deeper understanding of how SARS-CoV-2 neutralizing antibodies bind to the RBD and block the virus is crucial to determine novel vaccines and antibody-based therapies.