Why testing antibody production in patients?
The detection of antibodies produced in the host as a response to infection is suggested as a useful tool to evaluate past exposure to the virus. It is also an important information to determine how the antibody titer does or not correlate with viral protection.
Indeed, studies on Rhesus macaques showed that infection by SARS-CoV-2 generates a near-complete protection to reinfection (1), and limited cases of reinfection by SARS-CoV-2 have been evidenced in human. (2)
Detecting antibodies against SARS-CoV-2 is not useful for the diagnostic of COVID-19 but rather for a wide screening to estimate the prevalence and the fatality rate of coronavirus infection. Immunodiagnostic assays can also be a tool to determine if individuals can return to their social contacts. (3)
Figure : Antibodies evolution after SARS-CoV-1 infection. Based on Wu, et al. data (4)
Effective antigen-based tests could be an alternative to molecular testing. Viral antigens can be detected when the virus is actively replicating.
Antigen tests are rapid and highly specific but still may lack sensitivity. Thus, they can be used as a fast triage reducing the need for a molecular confirmation (3).
To improve diagnostic accuracy, one needs to develop and synthesize highly immunogenic, high-affinity viral antigens (3). Nowadays, several rapid test kits are under development or already available, i.e. using monoclonal antibodies against N protein of SARS-CoV-2(8).
Even if qPCR testing remains the method of choice for COVID-19 diagnostic, antigen testing is considered a good alternative to prevent the shortage of qPCR Reagents.
Antibodies against SARS-CoV-2 protein are coated on a plate.
- Biological samples from a patient potentially containing SARS-CoV-2 are added to the plate.
Labeled antibodies recognizing SARS-CoV-2-derived antigens are added to detect the presence of the virus in the sample.
- Signal detection
Based on data on SARS-CoV, among the four structural proteins, Spike and Nucleocapsid proteins are suggested to be the most immunogenic (6,7). More precisely the S1 subunit of SARS-CoV-2 Spike protein is considered the most suitable antigen because it has the least overlap with other coronaviruses. (6)
- Viral proteins or peptides are coated on a plate.
- Secondary antibodies recognizing human IgG or IgM are coated on a plate.
- Blood, plasma or serum, or potentially other biological fluids (like saliva) from a patient potentially containing anti-SARS-CoV-2 antibodies is added to the plate.
- Labeled secondary antibodies recognizing human IgG or IgM are added to detect the presence of anti-SARS-CoV-2 antibodies
- Labeled proteins or peptides are added to detect the presence of anti-SARS-CoV-2 antibodies
- Signal detection and antibody titer determination
Besides ready-to-use catalog peptides from SARS-CoV-2 proteins including critical peptide domains/regions or peptide substrates, we can synthesize custom peptides from simple to highly complex sequences.
We also offer custom manufacturing of Critical Raw Material (CRM) peptides for demanding applications.
We are producing recombinant proteins like Nucleocapsid protein, Spike protein or a domain thereof, or ACE2 receptor variants, do not hesitate to contact us. Some of them are already available!
We are ready-to-start immunization programs targeting Spike glycoprotein from SARS-CoV-2 and other antigens.
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