Coronavirus has made up much of the headlines in the last year, killing so many across the world and infecting countless more. The research for a vaccine is on and running but until a vaccine is in sight, doctors are trying to understand how the body builds immunity to the virus. Initially, antibodies seemed to be the obvious answer to this question, but recently that opinion has changed with more focus put on our body’s white blood cells, specifically T cells.
But what are T cells in the first place? T cells are a type of white blood cells which have various roles involving the body’s immunity and reaction to pathogens. T cells operate sometimes as ‘killer cells’ meaning that they attack infected cells but can also be ‘helper cells’, aiding B cells, another type of white blood cells, to make more antibodies for a specific pathogen.
Now that we know what T cells are, how do they help scientists and doctors in the fight against Covid-19? They help mainly in the area of testing for Covid-19. Usually, the main method of developing immunity for a pathogen is through the production of antibodies for that specific pathogen. However, with this new coronavirus, antibody levels decrease very quickly after exposure and recovery from Covid-19. This means that the original antibody immunity test used in many countries like the UK and the USA was not very useful as in many people antibodies are not the way humans become immune to the virus. This is where T cells come in. Covid-19 is similar to viruses like SARS and MERS as they are all various coronaviruses. This is why it makes sense that like SARS and MERS, long-term protection from Covid-19 is mainly based on T cell responsiveness. An example of this is shown through the original SARS. Singaporean researchers carried out a study into how responsive the T cells of people who had SARS 17 years ago, are when the virus is put into their bodies by doctors. The result is that the T cells responded very powerfully against the virus, while the antibody response to the virus was not as vigorous. This shows that T cell responses last for a long period, unlike antibody responses, in the case of SARS, MERS and Covid-19. Unfortunately, doctors and researchers have not yet understood why this pattern of results occur and have not fully proved that T cells are protecting the human body in the long term from these viruses even though they respond in large numbers. This shows why methods to test for T cell responses have to be focused on more than antibody testing which is less useful and reliable than T cell testing.1
Although T cells are a long-term method of the body protecting the body from Covid-19, another thought has to be considered. What happens to T cell response when thinking about cross-reactivity. Cross-reactivity takes into account if you have had a similar virus to Covid-19 before, like SARS. The question is whether this improves T cell responses to the virus. Furthermore, cross-reactivity’s effect on T cell response is also important as Covid-19 will form new coronaviruses in the future, in the same way, there is a slightly different flu every year. Using cross-reactivity, scientists need to understand whether exposure and being infected by the first version of Covid-19 affects the T-cell response of people to future coronaviruses. Therefore scientists must find out what T cell responses are typical for Covid-19
One common thought is that for one virus, the body makes one type of T cell multiple times. This could not be more wrong, as Professor Rosemary Boyton has said. “It looks like different sub-families of T cells may be important at different times during infection.”. She has said this because, as mentioned at the beginning of this article, killer and helper cells are different sub-families of T cells, which are used by the body at different times during infection from Covid-19. This means that researchers will need to know how and why killer cells respond to virus exposure with varying vigorousness compared to helper cells, and how to increase the level of response of T cells overall.2
To conclude, Covid-19 is a vicious virus with no vaccine as of date, but the change in focus from antibody immunity to T cells’ role in the immune system, will most surely save many more lives in the future.
- Hewings, Y., 2020. Antibodies Fight Off The New Coronavirus, But What Do T Cells Do?. [online] Medicalnewstoday.com. Available at: <https://www.medicalnewstoday.com/articles/antibodies-fight-off-the-new-coronavirus-but-what-do-t-cells-do#What-role-do-T-cells-play?> [Accessed 21 August 2020].
- Timmins, G. and Campus, S., 2020. T Cell Immunity: What Is It And How Does It Help To Protect Us From COVID-19? | Imperial News | Imperial College London. [online] Imperial News. Available at: <https://www.imperial.ac.uk/news/201833/cell-immunity-what-does-help-protect/> [Accessed 23 August 2020].