Question

If antigen already present in human body than how will differentiate that bacteria is also work as antigen ?

Answer 1

Antigens are proteins that are foundon the surface of the pathogen.The antibodies destroy the antigen(pathogen) which is then  engulfed and digested by macrophages. White blood cells can also  produce chemicals called antitoxins which destroy the toxins (poisons) some bacteria produce when they have invaded the body.
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