Testing for T cell immunity against the coronavirus is an important laboratory tool for evaluating immunity in individuals who have been diagnosed with COVID-19 or who have been vaccinated with any vaccine against SARS-CoV-2.
Evidence shows that both pillars of the immune system, antibodies and the T cell response (cellular immunity), are important for the functioning of the immune system against recurrences of SARS-CoV-2. Both specific IgG antibodies against the S1 subunit of the SARS-CoV-2 spike protein (S) and antigen-specific T cells play the most important roles in neutralizing the virus and maintaining immunity.
To be immune against SARS-CoV-2, one must be able to develop an adequate immune response to protect against future infection. This can be measured by looking for virus-specific antibodies in blood samples. Unfortunately, antibody responses decline normally over time and there are now many cases where people with a history of COVID-19 positive or vaccinated no longer have detectable antibodies. However, long-term protection against viruses comes not only from antibodies but also from cells of the immune system called T-cells or T-lymphocytes, which play a critical role in controlling and eliminating viral infections. There is a growing acceptance among immunologists that the T cell's immune response lasts longer and is necessary to establish an effective and protective immunity. The magnitude and time of the T-cell response that protects against re-infection remains unknown at present but is an area of intense scientific interest.
Cellular immunity test provides important information about the patient's response to the new SARS-CoV-2 coronavirus antigens, thus giving clinicians a better laboratory picture of how to manage their patients.
Clinical utility
Diagnostiki Athinon Coronavirus SARS-CoV-2 Test (COVID-19), T Cell Immunity, measures the response of T cells to specific antigens of SARS-CoV-2 (Spike protein).
Testing cellular immunity in this way is a useful tool in studies evaluating the cellular immune response in people infected or vaccinated against SARS-CoV-2.
Information on SARS-CoV-2
Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) is a positive, single-stranded RNA virus that causes coronavirus disease 2019 (COVID-19). Like other human coronaviruses, SARS-CoV-2 can cause infection of both the upper and lower respiratory system. Symptoms range from mild (such as the common cold) to severe (such as pneumonia) in both healthy and immunocompromised patients. Transmission of the SARS-CoV-2 coronavirus occurs mainly through respiratory droplets. During the early stages of COVID-19, the symptoms may be nonspecific and look like other common airway infections, such as the flu.
SARS-CoV-2 antigens and proteins
The SARS-CoV-2 monoclonal RNA genome encodes several different proteins, including spike (S), envelope (E), membrane (M), and nucleocapsid (N) proteins. The coronavirus got its name from the prominent glycoproteins that appear in the virus envelope (corona/crown). Spike glycoprotein consists of two subunits, S1 and S2. The S1 subunit contains the viral protein-binding region, i.e., the site that mediates the binding of the virus to the surface protein (mainly ACE2 protein) in human target cells. The S2 subunit is highly conserved among the various strains of the virus and is, therefore, a primary target for the development of most vaccines. Nucleocapsid (N) protein is a protein that binds to RNA and is necessary for the replication and transcription of the viral genome. N protein is also well conserved among the various coronaviruses and has also been shown to induce an immune response. Due to its high expression, it is detectable throughout the duration of the infection.
Cellular immunity to SARS-CoV-2
The immune status of people who have recovered from SARS-CoV-2 has been found to be highly variable depending on the severity of the infection, the treatments they have received, and the time elapsed since their recovery. In addition, the immune response developed by participants in vaccine trial studies is also variable and weakens over time. The ability of T cells to respond to SARS-CoV-2 antigen stimulation in a functional manner could be an important tool for assessing an individual's immune memory for the SARS-CoV-2 virus and indicate the level of protection against further infection with this virus.
How the test is performed
The new test of Diagnostiki Athinon is performed on a whole blood sample, which determines the activity of T cells against SARS-CoV-2 through the detection of Interferon-gamma, an important signaling molecule of the immune system released by T cells when they contact with the virus. The IGRA (Interferon Gamma Release Assay) methodology we use in the laboratory is fully documented and widely used in the testing of cellular immunity during tuberculosis (QuantiFERON®). The detection system is based on the standard ELISA technology.
The sensitivity of the test is 89.2% and its specificity is 98.9%. The test is performed with reagents certified for laboratory use (CE IVD).
