In Search Of Immunity

It seems the more we learn about COVID-19, the more menacing it becomes. Why are there so many symptoms? Are some of us already immune? As scientists race towards a vaccine, we report on the latest discoveries helping us understand how our immune system handles the infection

- Tom Ireland

WHY IS COVID-19 ABLE TO AFFECT PEOPLE SO DIFFERENTLY?

The wide range of outcomes of being infected with COVID-19 – from showing no symptoms at all, to rashes, severe respiratory illness and death – reflects the huge variation found in people’s immune systems. How the immune system responds to a virus such as SARS-CoV-2 is influenced by many factors, from our genes and general health to the other pathogens we’ve encountered in the past.

With COVID-19, there seems to be a critical period during which the immune system either mounts a protective response, stifling the virus and slowing its spread in the body, or a dysfunctional, inflammatory response, where the body starts to attack itself.

As part of a healthy immune reaction, local white blood cells recognise the virus as foreign and release chemicals called cytokines. These molecules help direct and amplify the body’s immune response, which can limit the spread of the virus and kill off infected cells. But the release of too many cytokines in a short period can start to cause collateral damage to healthy cells. In critical cases of COVID-19, the acute lung problems that are characteristic of the disease are caused by a ‘cytokine storm’ – a dangerous runaway overreaction of the immune system that creates even more inflammation and tissue damage than the virus.

“We know that as we age, our immune systems are not as good at clearing infections,” says Dr Elizabeth Mann, an immunologist who has been following the progress of COVID-19 patients arriving at hospitals across Manchester. “Older people are also predisposed towards the types of inflammatory immune responses that cause damage in COVID-19.”