Salivary COVID-19 (SARS-CoV-2, N) IgG ELISA Kit Overview
The Salimetrics® SARS-CoV-2 N-protein Salivary IgG ELISA kit is an enzyme-linked immunoassay specifically designed and validated for the qualitative measurement of human IgG specific to the SARS-CoV-2 Nucleocapsid protein (N-protein) in oral fluid.
It is intended for surveillance testing and not for diagnostic use. This assay kit was optimized and validated for performance in human oral fluid and has not been validated for other human sample types, such as human serum or plasma.
Surveillance testing for Antibodies can be used to determine if an individual may have been exposed to and infected with a virus, and also can be used to understand how many people in a population have antibodies (known as “surveillance tests,” or sero-surveys).
• When used for surveillance, the results can help determine how widely the virus has spread in communities and how far the pandemic has progressed. Results from tests used for surveillance only are generally not shared with individual patients and are critical for understanding the extent of and risk factors associated with infection.
• Testing individuals may help identify who has developed antibodies against SARS-CoV-2. The results of ongoing research are needed before it is known whether these antibodies are associated with protection from future infection. Current results can help inform who may qualify to donate blood that can be used to manufacture convalescent plasma.
Please read the complete kit insert before performing this assay. Failure to follow kit procedure and recommendations for saliva collection and sample handling may result in unreliable values.
The novel severe acute respiratory syndrome coronavirus 2 (SARS-Cov-2) was initially identified in the Winter of 2019 with an outbreak designation soon after at the end of the year. Since that time, the virus rapidly spready to achieve global pandemic status and quickly resulted in widespread containment and confinement public health measures in most countries throughout the world. These included shutdowns of schools, businesses, travel restrictions and physical/social distancing that had varying degrees of success resulting in a continued global circulation of the virus. With the current infection rates in the US and resurgence in many countries, elimination of the virus is no longer possible and more long-term strategies to minimize the health and economic impact will be needed for years to come.
In addition to virus exposure, there is an urgent need to better understand the levels and duration of protective immunity for public health considerations. Adding serology will help in this effort and many serum assays are available in many formats, however for larger scale efforts to measure disease incidence, there is a need for an at home painless collected sample that simultaneously minimizes exposure risk of patient and healthcare worker that can be met with an oral fluid offering. Our assay will meet the technical need for high sensitivity and specificity performance in saliva for central testing at scale. The main source of salivary IgG antibodies is the serum, so it is not surprising that salivary IgG antibodies directly reflect the specificity and activity of those found in serum (2, 3). Oral fluid is thus an easily accessible surrogate to serum or plasma in this regard and enables salivary serology studies, surveillance tests or sero-surveys (1). Testing can help determine who has developed antibodies against SARS-CoV-2. Importantly, we have determined that human IgG withstands conditions commonly used for viral heat inactivation (60 or 65 C for 30 min and 95 C for 5 min). The main utility of antibody tests for SAR- CoV-2 supported by the WHO, CDC, FDA and AMA are surveillance studies and the Salimetrics N-protein IgG ELISA kit meets this need.
Antibody levels decrease in the serum of COVID19 patients over time (4, 5) and vary depending on disease severity (6). In fact a higher number of asymptomatic participants become seronegative at 60 days indicating a true decline over a 2-month period rather than an artifact of assay performance (4, 5). Therefore, our assay is benchmarked on validated commercial serum kit performance instead of molecular tests. Maximizing the likelihood of antibody detection, N protein was chosen as an advantage since it represents the most immunodominant protein in the coronavirus family.
Antibody levels decrease in the serum of COVID19 patients over time and vary depending on disease severity. In fact a higher number of asymptomatic participants become seronegative at 60 days indicating a true decline over a 2-month period rather than an artifact of assay performance. Therefore, our assay is benchmarked on validated commercial serum kit performance instead of molecular tests. Maximizing the likelihood of antibody detection, N protein was chosen as an advantage since it represents the most immunodominant protein in the coronavirus family.
SALIVARY COVID-19 (SARS-CoV-2) IgG ASSAY PRINCIPLE
This is a salivary serological ELISA kit where viral antigen is coated on microtiter plates and human antibodies in test samples are detected using an Anti-Human IgG detection antibody linked to horseradish peroxidase (HRP). After each incubation, unbound components are washed away. Anti-Human IgG HRP Enzyme Conjugate is then added and the levels measured by the reaction of the HRP enzyme to the substrate tetramethylbenzidine (TMB). This reaction produces a blue color. A yellow color is formed after stopping the reaction with an acidic solution. The optical density is read on a standard plate reader at 450 nm. The total amount of anti-IgG HRP Enzyme Conjugate detected is proportional to the amount of anti-SARS CoV2 IgG present in the sample. Qualitative cutoff values are determined for each run based on controls provided in the kit and serostatus determined from values obtained by oral fluid testing. The cutoff OD is used to divide sample OD values to produce signal/cutoff ratio in a simple calculation with values above 1.1 positive and below 0.8 negative. Samples reading between these values are considered borderline and a second test is recommended for these samples or a second collection.
References & Salivary COVID-19 Research
1. Randad, PR., et al. (2020). COVID-19 serology at population scale: SARS-CoV-2-specific antibody responses in saliva. medRxiv.
2. Hettegger, P., et al. (2019). High similarity of IgG antibody profiles in blood and saliva opens opportunities for saliva based serology. PloS one. 2019;14(6):e0218456.
3. Heaney, JLJ., et al. (2018). The utility of saliva for the assessment of anti-pneumococcal antibodies: investigation of saliva as a marker of antibody status in serum Biomarkers. 23(2):115-22.
4. Patel, M., et al. (2020). Change in Antibodies to SARS-CoV-2 Over 60 Days Among Health Care Personnel in Nashville, Tennessee. JAMA.
5. Vabret N. (2020). Antibody responses to SARS-CoV-2 short-lived. Nat Rev Immunol. 20(9):519.
6. Long QX., et al. (2020). Antibody responses to SARS-CoV-2 in patients with COVID-19. Nat Med. 26(6):845-8.