Why We Need T-Cells, As Well As Antibodies, In The Fight Against Covid

A quick and easy guide to how it all works.
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Forget Batman and Robin for a second, antibodies and T-cells are the only superhero duo we need right now.

Prior to 2020, most people didn’t even know what a T-cell was. But now we’re increasingly learning that they might hold some hope in the fight against Covid-19.

T-cells are a type of white blood cell which specialise in tracking down virus-infected cells and killing them (a bit like your body’s version of Liam Neeson in Taken).

Studies suggest they can remember the virus that causes Covid-19 – called SARS-CoV-2 – for a lot longer after having the illness than antibodies can, which may be helpful in staving off future reinfection.

So how does it all work then?

When Covid-19 enters the body, it attaches to our cells, hijacks them, and then creates copies of itself to invade even more cells. Our immune system kicks in to try and stop this, sending out its frontline defence – the ‘innate immune response’ – to deal with the intruder.

This is the default response to any virus entering the body. As part of this initial response, inflammatory proteins called “interferons” are released, which have antiviral functions. The aim is to stop the virus in its tracks – though we don’t actually know how well this first response works in fending off infection.

While the innate immune system is trying (and sometimes failing) to fight off the virus, it also ‘talks’ to the more specific ‘adaptive’ immune response. This is your body’s tailor-made solution for dealing with Covid-19, and involves the release of B-cells, which produce antibodies, as well as T-cells, which kill infected cells.

While a lot of hope has previously been pinned on the antibody response, we now know antibody levels tend to wane around three to four months after infection, which isn’t ideal.

But that’s not to say it’s all doom and gloom, and that loads of people are going to get reinfected multiple times (only a relatively small number of people have been confirmed to have had Covid-19 twice).

Because there’s a growing body of evidence to show that in the absence of antibodies, T-cells are also important in the fight.

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One study from the Karolinska Institute and Karolinska University Hospital in Sweden (originally was published as a preprint paper, but since peer-reviewed) revealed many people with mild or asymptomatic Covid-19 demonstrated “T-cell-mediated immunity” – even if they did not test positively for antibodies.

According to researchers, this means public immunity is probably higher than antibody tests suggest. However it’s a bit trickier to analyse T-cells compared to antibodies, as it needs to be done in specialised laboratories. Hence why there’s no magic T-cell test yet, which can tell you if you’ve had the virus or not.

A recent pre-print study, this time by the UK Coronavirus Immunology Consortium and Public Health England (PHE), found people who had mild to moderate or asymptomatic Covid-19 still showed “robust” T-cell immunity six months after infection. Not all T-cell responses were equal however – those who had symptoms were found to have far more T-cells than those without.

Dr Shamez Ladhani, consultant epidemiologist at PHE and one of the study’s authors, told the Evening Standard: “Early results show that T-cell responses may outlast the initial antibody response, which could have a significant impact on Covid vaccine development and immunity research.”

The study monitored the T-cell immune response to SARS-CoV-2 from 100 infected health care workers over a six month period, and compared this to 2,000 uninfected health care workers – so it can’t tell us much about immune responses in children or the elderly.

That said, a study from the US, which analysed blood from people with Covid-19, showed the immune systems of patients older than 80 produce fewer T-cells compared to younger patients, which might go some way in explaining why older people are more susceptible to severe illness.

Professor Charles Bangham, chair of immunology at Imperial College London, pointed out that previous observations of T-cell immunity to SARS have shown similar results – with some patients displaying T-cell immunity more than 10 years after infection, “though we don’t yet know whether this will be the case with Covid-19”.

Experts are still learning about Covid-19. The information in this story is what was known or available at the time of publication, but guidance could change as scientists discover more about the virus. To keep up to date with health advice and cases in your area, visit gov.uk/coronavirus and nhs.uk.

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