Cytokine storm

An overreaction of the body's immune system

By Alison George

Diseases such as covid-19 and influenza can be fatal due to an overreaction of the body’s immune system called a cytokine storm.

Cytokines are small proteins released by many different cells in the body, including those of the immune system where they coordinate the body’s response against infection and trigger inflammation. The name ‘cytokine’ is derived from the Greek words for cell (cyto) and movement (kinos).

Sometimes the body’s response to infection can go into overdrive. For example, when SARS -CoV-2 – the virus behind the covid-19 pandemic – enters the lungs, it triggers an immune response, attracting immune cells to the region to attack the virus, resulting in localised inflammation. But in some patients, excessive or uncontrolled levels of cytokines are released which then activate more immune cells, resulting in hyperinflammation. This can seriously harm or even kill the patient.

 Cytokine storms are a common complication not only of covid-19 and flu but of other respiratory diseases caused by coronaviruses such as SARS and MERS. They are also associated with non-infectious diseases such as multiple sclerosis and pancreatitis.

The phenomenon became more widely known after the 2005 outbreak of the avian H5N1 influenza virus, also known as “bird flu”, when the high fatality rate was linked to an out-of-control cytokine response.

Cytokine storms might explain why some people have a severe reaction to coronaviruses while others only experience mild symptoms. They could also be the reason why younger people are less affected, as their immune systems are less developed and so produce lower levels of inflammation-driving cytokines.

In 2006, six healthy young men were left in intensive care with multiple organ failure as a result of an out-of-control cytokine immune response during a preclinical trial of a new kind of drug. This reaction happened just 90 minutes after receiving a dose of the drug.

 Source: New Scientist