What is an antigen?
An antigen is a marker that tells the immune system whether there is a harmful body in the body.
An antigen is located in viruses, bacteria, tumors, and normal cells of the body.
An antigen, as a marker, indicates a foreign body to the body - the immune system produces antibodies in response and begins to destroy the harmful antigen.
It is worth noting that the immune system remembers the antigen once it has entered and, in the event of repeated infection, destroys this foreign body much more easily and in a short time - this process is called immunological memory.
During antigen testing, blood, urine, feces, saliva, or other body fluids are examined for specific markers of the disease.
An antigen test can diagnose viral infection, monitor the condition, and screen, as well as determine whether a donor is suitable for transplantation.
Source:
https://my.clevelandclinic.org/health/diseases/24067-antigen
