What is cytokine storm?

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People with Covid-19 can experience an extreme immune system response known as cytokine storm. Dr Alaeus, Head of Infectious Diseases at Livi, explains

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Quick facts

  • Cytokine storm increases the risk of serious complications from Covid-19
  • It happens when the immune system attacks the body’s healthy tissue
  • Doctors are now starting to spot the early signs
  • Medications can be used to reduce the risk of cytokine storm

We often see advice about ‘boosting’ the immune system. But an effective immune response is a balancing act that involves releasing the right chemical messengers and defenders, in the right amounts, at the right time.

If that goes wrong, all sorts of things can happen. Reactions like allergic asthma and hay fever, and auto-immune conditions like rheumatoid arthritis, multiple sclerosis and psoriasis are all examples of the body triggering an immune response when it should not.

Cytokine storm is an example of one such auto-immune malfunction. This is how it works.

How your immune system fights disease

Immune responses are driven by a family of chemical messengers known collectively as cytokines, that are released by the immune system to help fight illness.

When the body perceives a threat, or tissues are damaged by an injury, bacteria, or virus, this triggers the release of pro-inflammatory cytokines. These quickly go to work recruiting and activating immune cells to fix the problem.

These inflammatory cytokines increase blood flow and instruct blood vessels to leak fluid into surrounding tissues. This leads to swelling, designed to trap foreign substances and stop them coming into contact with healthy tissue. It’s all part of the healing process.

These chemical messengers also step up production of T-cells and other ‘defender cells’. These seek out and destroy invaders such as viruses and bacteria.

In the short term, this flurry of activity by the immune system protects healthy tissue and promotes healing.

But in the long term it’s not sustainable. So, our immune system also has a collection of anti-inflammatory cytokines, which put the brakes on these inflammatory responses. This should happen when the job of healing is done and you’re getting better.

Cytokine storm — an immune system in overdrive

If this does not happen, the immune system continues its fighting process but then starts to damage healthy tissue. This happens with auto-immune conditions like multiple sclerosis and rheumatoid arthritis. It also happens to some Covid-19 patients — known as cytokine storm.

When these anti-inflammatory cytokines cannot switch off, they cause more inflammation. That leads to more cells damaged, and more pro-inflammatory cytokines flooding the body.

As a result, blood vessels can become so leaky that the lungs fill with fluid, and blood pressure drops – which reduces oxygen levels throughout the body. Blood begins to clot, which further reduces blood flow to vital organs. As organs begin to fail, patients can go into shock and face permanent organ damage, or in the worst case, death.

How spotting the early signs of cytokine storm is saving lives from Covid-19

Unsurprisingly, cytokine storm dramatically increases the risk of becoming seriously ill with Covid-19, and it is thought to be a factor in most Covid-related deaths.

But the good news is that this knowledge is already saving lives and improving outcomes.

It’s early days but by spotting the signs of cytokine storm, doctors are beginning to find ways of taking steps to help prevent it from making a patient seriously ill.

These signs include raised blood levels of certain inflammatory biomarkers. By checking for these markers, doctors are starting to identify patients most at risk and treat them before cytokine storm takes hold.

Steroid medication can be used to damp down inflammation and minimize tissue damage, especially in the lungs, while blood-thinning drugs can be administered to prevent potentially life-threatening blood clots. ‘The use of steroids and blood-thinning drugs were 2 major milestones in the standard of care at the intensive care units during spring to help prevent life-threatening serious complications for Covid-19 patients’.

However, there’s still a lot that doctors don’t know about cytokine storm, and the different chemical messengers that switch inflammation on and off. There are no simple answers.

Genetics, individual immune memory, and any number of other factors such as our general health and nutrition, are all likely to influence our immune system responses.

What’s needed now is more research to work out how, and when, to accelerate our immune responses to Covid-19: and how, and when to put the brakes on before they can spiral out of control.

This article has been medically approved by Dr Annette Alaeus, Head of Infectious Diseases at Livi.

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