Why immune system in some people cannot fight COVID-19 effectively

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Older people and people with underlying medical conditions are at particular risk of severe COVID-19.

In a new study, researchers have found one possible reason for this vulnerability.

While these risk groups produce greater quantities of an important type of immune cell known as “T-helper cells,” their T-helper cells show impaired function.

This ‘molecular brake’ on the immune system could serve as a potential new treatment target in patients with severe COVID-19.

The research was conducted by a team from Charité – Universitätsmedizin Berlin.

Soon after the emergence of COVID-19, medical experts from across the globe reported the same phenomenon.

They found that older people and people with underlying medical conditions (such as cardiovascular disease and diabetes) were more likely to develop severe disease.

There is likely an array of medical reasons why advancing age or health problems should make it more difficult for our bodies to fight infection with SARS-CoV-2.

One of the factors suspected of playing a major role in this regard was the immune system. An interdisciplinary team of researchers from Charité has collated findings which support this hypothesis.

As part of their study, the researchers collected blood samples from 39 COVID-19 patients who had been admitted to Charité for treatment.

They used these blood samples to isolate immune cells which they then stimulated with specially synthesized fragments of the SARS-CoV-2 virus.

Using specific dyes to make them visible, the researchers then counted T-helper cells which had reacted to the viral fragments.

As the last step, they tested whether there might be a link between the number of activated T-helper cells and the patients’ risk factors.

The team was able to show a positive link between the frequency of virus-specific T-helper cells and the patients’ age.

The same positive link was found to exist in relation to the “Comorbidity Index,” a compound measure expressing the severity of 19 different underlying medical conditions: the higher the patient’s Comorbidity Index, the higher the number of SARS-CoV-2-specific T-helper cells in their blood.

However, the team also found that advancing age and overall comorbidity scores were linked to a decrease in the proportion of cells producing the messenger substance interferon-gamma (IFN-γ).

Cells normally release this molecule when they have recognized a virus; it is used to stimulate other components of the body’s immune response which are needed to fight the pathogen.

The team says some of the SARS-CoV-2-specific T cells which they found in the blood of COVID-19 patients with risk factors no longer function properly.

One might say that these T-helper cells are being slowed down in people with risk factors. The team believes this has the potential to hamper the body’s ability to mount an effective response against the pathogen.

One author of the study is Dr. Arne Sattler, a researcher in the Translational Immunology Research Group.

The study is published in the Journal of Clinical Investigation.

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