What are antibodies and why do we develop them?

Antibodies are protein alarm bells, which warn the immune system that a threat has been detected inside the body. “We all have cells primed to make antibodies called immunoglobulin M (IgM),” explains virologist Dr Sarah Pitt, a lecturer at the University of Brighton and fellow of the Institute of Biomedical Science. “These are the first response to a danger like Covid-19. They are capable of binding on to something like the coronavirus, marking them for white cells in the body to attack.”

IgMs appear within a few days of infection, can be detected in a lab within a week and are made by the body for a few months.

Following on are antibodies called immunoglobulin G (IgG) that are more finely tuned to pick up the virus. Says Dr Pitt: “These IgGs stick around in the bloodstream for longer than IgM antibodies. We don’t know exactly how long for in the case of Covid-19, but it might be a couple of years in some people.”

When you encounter a virus that the body recognises, it can create these antibodies faster, meaning your immune system could get on top of a disease, possibly before you even know you have had it.

Who makes most antibodies?

“We know that you make more antibodies,” says Dr Pitt, “if you are seriously ill than if you are only slightly affected. But at least 10 per cent of people do not make any antibodies no matter how sick they get, and we don’t know who that 10 per cent are yet.” These are likely to be the mildly affected and would not be immune even if they recovered.

Are high levels an advantage?

Not always. Dr Pitt explains: “We know that even if you do make plenty of antibodies, that number will reduce quite fast, certainly over a few years. By the end of this year, it is possible that most people will have lost any antibodies they made and in about two to three years’ time, everyone might have lost them. That means for most people the body would have to start again if Covid-19 came around again.” What would be true is that if you had high levels once and re-encounter Covid-19, your immune system would recognise it more quickly and start a fast-immune response. But, if you produced a low level of antibodies or none the first time, you may well end up just as poorly a second time.

How could you beat Covid-19 but not have antibodies?

“People get common colds all the time,” says Dr Pitt, “but their blood doesn’t show antibodies so it’s possible they were at a low level and disappeared quickly. With common colds, that doesn’t matter as much as it does for Covid-19. It is possible that over time this new coronavirus will mutate into a milder form for which the body will not need to produce many antibodies either.”

So why test for antibodies?

Dr Pitt is not sure there is any useful purpose. “Producing antibodies once does not mean you will have immunity forever. And knowing that you have had Covid-19 is not much use in itself as we know antibodies do not last.”

Do we have a standard global antibody test yet?

No, says Dr Pitt, although a number are under evaluation.

Could antibody testing mean herd immunity might work?

“You can’t get herd immunity outside a vaccination programme,” says Dr Pitt. “We didn’t get on top of measles until there was a vaccination programme in place.” She points out that as many people don’t make many antibodies — and they don’t last long — it is possible to catch it more than once. So herd immunity would never develop naturally unless the majority of the population catch and recover from the virus, and then also make a long-lasting immune response.

If you have antibodies, would you need a vaccine?

Yes, says Dr Pitt. Antibodies don’t guarantee you won’t fall ill. They only act to alert the body to start defending itself, but a vaccine tricks the body into being in constant readiness.

She says antibody testing might have to be carried out with vaccination as if the body already had antibodies, the vaccine might not work.

Can antibodies be used in medical treatment?

Studies under way are seeing if transfusions of antibody-rich plasma can help patients seriously ill with the disease. “The idea is that the antibodies would help to mop up the virus for the immune system,” says Dr Pitt.

What about the Roche test?

This is a new antibody test with a reportedly high accuracy rate but it has yet to be independently evaluated in the UK. Using Roche lab equipment, blood can be tested in 18 minutes. Roche expects to produce 100 million of its new tests monthly by the end of 2020.

The Daily Telegraph

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