Cytokine Storm

Of all the possible compounding effects of COVID-19, the disease caused by the novel coronavirus, the cytokine storm is one of the most feared.

• Cytokines are small proteins released by many different cells in the body, including those of the immune systemwhere 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 coronavirusessuch 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.

How does our immune system work?

• The immune systems in our bodies protect us from bacteria, viruses, and parasites by removing them from our systems.
• The immune system gets activated by things that the body does not recognise as its own. These things are called antigens, and include bacteria, fungi and viruses.
• An effective immune system response involves inflammation, an important and indispensable part of the process.
• Inflammation has an important protective function. The release of inflammatory mediators increases the blood flow to the area, which allows larger numbers of immune system cells to be carried to the injured tissue, thereby aiding the repairing process.
• However, if this inflammatory response is not regulated, very dangerous consequences can follow.
• This is when a ‘cytokine storm’ can be triggered. The damage to the surrounding cells can be catastrophic, leading to sepsis and potentially, death.

What is role of cytokines in the immune system?

• Evidence is emerging that a subset of the infected patients develop severe COVID-19because of an overreaction of their immune systems, which triggers cytokine storm syndrome (CSS).
• While various studies have shown that the disease has more severe consequences for those above the age of 60 years, and especially those with existing co-morbidities such as heart disease, diabetes, hypertension, chronic respiratory disease and cancer, some countries have also reported deaths of younger people, including teenagers, after catching the infection.
• Cytokines are signalling proteins that are released by cells at local high concentrations — a cytokine storm or CSS is characterised by the overproduction of immune cells and the cytokines themselves because of a dysregulation in the process.
• A severe immune reaction, leading to the secretion of too many cytokines in the bloodstream, can be harmful since an excess of immune cells can attack healthy tissue as well.

A cytokine storm can occur due to an infection, auto-immune condition, or other diseases. Signs and symptoms include high fever, inflammation (redness and swelling), severe fatigue, and nausea. Cytokine storms are not exclusive to coronavirus patients. It is an immune reaction that can occur during other infectious and non-infectious diseases as well.