Immuno-T FAQs

Frequently Asked Questions

What is a ‘T cell’?

A T cell is a cell of the immune system that helps orchestrate immune responses against specific stimuli, namely bacteria, viruses, even cancer cells. The cells develop in the thymus gland, hence the name “T” cell. Following an infection with a virus, long-lived memory T cells are formed. Memory T cells are important as they are able to quickly divide into large numbers upon re-exposure to viruses, thus protecting from illness. This test measures for the presence of memory T cells that specifically recognise SARS-CoV-2, the virus that causes COVID-19.

What is ‘IFN-ɣ’?

‘IFN-ɣ’ stands for interferon gamma. This is a cytokine produced by T cells and forms a critical part of your immune response to viral infection. It can also directly prevent viruses from replicating. In the laboratory, we measure the amount of IFN-ɣ produced by your T cells when we expose them to particular fragments of the SARS-CoV-2 virus. The value is in picograms per millilitre (pg/ml) of whole blood.

What do the SARS-CoV-2 T cell test result classifications mean?

The ‘high’, ‘average’, ‘low’ and ‘undetectable’ result classifications to grade your T cell response are
based on our prior research studies that assessed the SARS-CoV-2 T cell responses in a broad range of individuals across the UK. This study identified that individuals with a relatively high T cell response were better protected from COVID-19 than those with a relatively low or undetectable response. Your result is based on the amount of IFN-ɣ your T cells have produced in response to SARS-CoV-2, and classified as follows:
‍
- HIGH – Over 141.6 pg/ml IFN-ɣ
- AVERAGE – Between 23.7 and 141.6 pg/ml IFN-ɣ
- LOW – Between 7.8 and 23.7 pg/ml IFN-ɣ
- UNDETECTABLE – Below 7.8 pg/ml IFN-ɣ

My T cell result is ‘undetectable’ but the IFN-ɣ value says ‘<7.8 pg/ml’?

This value represents the sensitivity of our laboratory test; our test cannot accurately quantify values below this amount. Any test condition stating this value would be deemed ‘undetectable’.

What is an antibody? / What is IgG?

Antibodies are produced by B cells and form another critical part of your immune response to viral infection by recognising and immobilising viruses. Most of the vaccines currently approved for use in the UK generate a certain type of antibody termed IgG which react to the ‘Spike / Receptor Binding Domain’ part of the virus. Natural infection usually also induces IgG responses to other parts of the virus, e.g. ‘Nucleocapsid’. The quantity of IgG is provided in units per microliter (U/μl) of blood plasma. Each test is positive if this value is above 2.5 U/μl.

Does a ‘high’ or ‘average’ T cell test result protect me from COVID-19 in the future?

Whilst our prior research study identified that individuals with a ‘high’ or ‘average’ T cell response were relatively better protected against COVID-19 than individuals with a ‘low’ or ‘undetectable’ response, we do not know whether this same response is sufficient to protect you from future SARS-CoV-2 infections, in particular to variants of COVID-19. Therefore, no inference must be made from a ‘high’ or ‘average’ test result and effective immunity from future COVID-19. It is also important to note that this test is not a diagnostic for prior SARS-CoV-2 infection; the result only indicates the presence of T cells specific for the virus, which could also have arisen from vaccination and/or cross-reactive responses to other human coronaviruses.

Does a ‘low’ or ‘undetectable’ T cell test result mean lack of prior COVID-19 or vaccine not working?

No inference can be made from a ‘low’ or ‘undetectable’ test result and lack of immunity to SARS-CoV-2 (COVID-19) since other parts of your immune response, e.g. antibodies specific for SARS-CoV-2, may also protect you independently of T cells. It is still possible that you encountered the virus or received a COVID-19 vaccine but you didn’t mount a sufficient T cell response to it, or a T cell response can no longer be measured. Alternatively, our test may not be sensitive enough to detect all T cells induced by prior infection and/or vaccination.

Frequently Asked Questions

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Frequently Asked Questions

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