What is a cytokine storm?
“I read that the immune system can become more dangerous than the diseases it protects against if it triggers a cytokine storm. But what is that, and what causes it?
The immune system can sometimes react so violently that it poses a greater threat to the patient than the disease it is combating. One of the most dangerous examples of an hyperactive immune system is the phenomenon known as a cytokine storm. Cytokines are a group of neurotransmitters that the body releases as part of the immune system’s defence. The cytokines activate different types of white blood cells and cause some of the symptoms of disease, such as fever. A cytokine storm results when the immune system overreacts and releases too many cytokines, causing a self-perpetuating reaction that can get out of hand. Some of the cells that the cytokines activate produce even more cytokines, and the ongoing increase can cause such severe inflammation that the body can go into shock, or organs into failure. Kidneys can shut down, or the liver can stop working, so that the patient ends up dying.
Examples of cytokine storms have been particularly frequent in connection with bronchial infections caused by coronavirus such as COVID-19 and the flu. The Spanish Flu pandemic that swept the world in 1918-1920 was the first disease for which cytokine storms were confirmed to contribute to the high death rate. It was particularly out of control during the second wave in September 1918, when 1 in 40 infected people died. To find out if a cytokine storm could be part of the explanation, scientists in 2005 infected a group of macaques with Spanish Flu. The results were clear: the monkeys’ immune systems caused death after a few days.