Antigens are substances that cause a person’s immune system to react, either mildly or severely. A person’s system will detects antigens as foreign matter and try to eliminate them through the production of antibodies (which help neutralize antigens). Some antigens and antibodies can be inherited from either parent or both, and their presence may be used to determine vital information about body systems. One such example is blood typing, which looks for certain antigens on the surface of red blood cells.