An adult human’s immune system is made up of more than 1 trillion cells. In total, it weighs around 1 kilogram, depending on the size of the person
By Chen Ly
23 October 2023
Lymphocytes, a type of white blood cell that make up part of the immune system
Getty Images/Science Photo Library
Your immune system could weigh 1 to 1.2 kilograms and contain 1.8 trillion cells.
“The immune system is a complex system comprising many different cell types with essential functions,” says Ron Milo at the Weizmann Institute of Science in Israel.
Lymphocytes, for example, are a type of white blood cell that produce antibodies to neutralise viruses and other pathogens. Mast cells, another component of the immune system, control the body’s inflammatory response to injury.
Advertisement
To get a better insight into what constitutes a person’s immune system, Milo and his colleagues took a census of all its cells. Using measurements from past research, they estimated how many immune cells were in different tissue types around the body.
They combined this with laboratory analyses of samples of every tissue type, which they collected from several men and women of approximately the same age, as well as children, all aged 10 years old. None of the participants had any known health conditions.
The team found that a 73-kilogram man who was aged between 20 and 30 years old would have around 1.8 trillion immune cells that collectively weigh 1.2 kg. A 60 kg woman of the same age has 1.5 trillion immune cells, weighing 1 kg. The cell number declines to 1 trillion for a 10-year-old child, whose immune system weighs around 0.6 kg.