- Cytokines are proteins released by immune system in response to infection
- Cytokine storm is a hyper reaction of the immune system and kills good cell
- Cytokine storm can cause multiple organ failures
New Delhi: As scientists and the medical community across the world are struggling to tackle the COVID-19 pandemic, they are continuously learning something new about it. One of the mysteries of the novel coronavirus- SARS-CoV-2, according to experts, is that it causes only mild to moderate symptoms in most people but turns out to be fatal for others causing multiple organ failure and even death. The answer to this mystery, according to experts, could lie in the emerging evidence that in many cases, severe COVID-19 may be driven by an overreaction of their immune systems against the infection where the body starts to attack its own cells and tissues, rather than the virus itself. This abnormal immune response to the infection is called ‘cytokine storm’, which experts say, is one of the fuelling agents of COVID-19.
What Are Cytokines And Cytokines Storms?
According to Dr Raman Dhara, Additional Professor, Indian Institute of Public Health (IIPH), Hyderabad, cytokines are small soluble molecules or proteins released by the immune system in response to an infection that act as messengers for the immune system. As they attract immune cells to counter the infection, which can be of any kind, cytokines trigger inflammation, he said.
Dr Aviral Roy, Consultant Critical Care, Medica Superspecialty Hospital explained the cytokines by comparing the immune system fighting infections in the body to an army of soldiers combating infiltrators. He said,
Suppose, a terrorist infiltrates in a country. For the first 3-4 day, nobody gets to know about it. Then one of the soldiers picks it up and tell his team that there’s some suspicious activity going on. He communicates this to everybody else including the commanding authorities and asks about what needs to be done with the infiltrator. This communication system in your body is called cytokine. It takes the message from one cell to another about where the virus is in the body and how to attack it. So cytokine is your immune system’s signalling agent.
He further said that the cytokine storm is when the immune system loses the ability to identify the good cells from virus affected or bad cells. He said,
In cytokine storm, the immune system which is originally attacking the virus, now, goes into hyperdrive and basically starts destroying all cells.
Cytokine storm is when a hyperimmune reaction occurs and abnormally high quantity of cytokine proteins are released into the blood too quickly, explained Dr Dhara. He added,
In simpler words, Immune response is more than it should be!
While normally cytokines regulate immune responses, in hyper reaction case they cause harm and can even cause death.
The Role Of Cytokines Storms In Severe COVID-19
Experts said that cytokine storms have been observed in several individuals who are critical with COVID infection. A study named ‘COVID-19: Pathogenesis, cytokine storm and therapeutic potential of interferons’ published in Elsevier Public Health Emergency Collection, accessible in PubMed Central (PMC) repository of the National Institute of Health (NIH), USA, says that acute respiratory distress syndrome (ARDS) is the main cause of death in COVID-19 disease. It further states that one of the main features of ARDS is the cytokine storm – an uncontrolled systemic inflammatory response resulting from the release of pro-inflammatory cytokines by immune activated cells. As per the study, high blood levels of cytokines have been detected in patients with COVID-19 infection.
High cytokines flow suppresses oxygen utilisation in the body and cause hypoxia- the state of insufficient oxygen as it kills cells, which leads to multiple organ failure like kidney failure, heart failure and even impacts the functioning of the brain. Dr Roy said,
In a COVID-19 patient, cytokine storm starts in lungs, which is why the lungs get affected initially, then as the storm loses control and starts attacking other organs which lead to multi-organ failure. As oxygen starts decreasing in the body, it starts working inefficiently including the immune system.
Can Preventing Cytokine Storm Ease Severe COVID-19 Symptoms?
“Cytokine storms are called storms because they are unpredictable and uncontrollable”, said Dr Roy adding that preventing cytokine storm is not possible and it can be only modulated to some extent with help of immunomodulation medicines. He said,
There is no way to prevent the cytokine storm. It is not possible to stop cytokine from working because, in the absence of cytokine, the virus itself will the patient. The storm can only be modulated via immunomodulators that can keep the immune system active and at the same time not attacking all cells.
Dr Dhara added that modulating the cytokine storm can dampen the hyper inflammation and lessen the collateral damage caused by the runaway reaction. He said,
Various drugs such as anti-tumour necrosis factor, cyclooxygenase inhibitors, are potential cytokine storm inhibitors. Some of them are currently in clinical trials for COVID-19.
According to experts, cytokine storms are not unique to COVID-19 infection and happen in patients with any kind of severe infection like bird flu caused by H5N1 influenza virus, Middle East respiratory syndrome coronavirus caused by MERS-CoV, and others.