immune system

system which forms antibodies and works against foreign bodies that attack the body

An immune system is a collection of mechanisms within an organism that protects against disease by identifying and killing pathogens and tumor cells. It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own healthy cells and tissues in order to function properly. Detection is complicated as pathogens adapt and evolve new ways to successfully infect the host organism.
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A complex system that is responsible for distinguishing us from everything foreign to us and for protecting us against infections and foreign substances.

[im-YOON]
The complex group of organs and cells that defends the body against infections and other diseases.

the body's system for protecting itself from viruses and bacteria or any "foreign" substances.