A new study conducted by scientists at the Weizmann Institute of Science in Israel found that the adult immune system is composed of 1.8 trillion cells, which weighs about 1 kilogram to 1.2 kilograms based on different people's physiques. The relevant paper was published in the latest issue of the Proceedings of the National Academy of Sciences.

The immune system is a complex system that includes many cells with important functions. To better understand the makeup of the human immune system, the research team conducted a census of all its cells. Using previous measurements, they estimated how many immune cells there were in the body.

They found that a man aged between 20 and 30 years old and weighing 73 kilograms had about 1.8 trillion immune cells in his body, with a total weight of 1.2 kilograms. A 60-kilogram female of the same age has 1.5 trillion immune cells in her body, with a total weight of about 1 kilogram; while the immune system of a 10-year-old child weighs about 0.6 kilograms and has less than 1 trillion immune cells.

The research team pointed out that lymphocytes and neutrophils (another type of white blood cell) accounted for 40% of the number of all immune cells and 15% of the total mass of the immune system in both men and women, children and adults. Although these cells are commonly called white blood cells, most are found primarily in the bone marrow and lymphatic system, with only a small percentage circulating in the blood.

In addition, macrophages that engulf pathogens are the heaviest immune cells, accounting for almost half of their total mass even though they only account for 10% of the total number of immune system cells.

The latest research is expected to help scientists create infection models and develop effective clinical treatments based on them.

(The original title is "Containing 1.8 trillion cells, the human immune system weighs about 1 kilogram")