Immune system cells differentiate between self and foreign cells by their antigens.
The immune system is the composition of various organs tissues and cells that work in coordination to protect the body from foreign invaders like bacteria, viruses, etc. There are two types of immune systems: the active immune system and the passive immune system.
Antigen can be a complete microorganism or a structure present upon the body of the microorganism that can trigger the body of the host and cause damage or diseases. The antibody present inside the body of host identifies this antigen and fights to protect the body.
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