In the human body, what word describes any foreign substance which induces an immune response?

Pathogen is the answer to this, an antigen is an indicator in the blood, of what type of illness, disorder maybe in evidence in the person, antigens give doctors the direction as which to go in regards to treatment.. Better information needs to be supplied..

MatteusMaximus, a pathogen is a subststance that enters your body and males you sick like the flu