immune system- antibodies and antigens

• An antigen is a marker (an alert) that tells your immune system whether something in your body is harmful or not. 

  Antigens are found on viruses, bacteria, tumours and normal cells of your body. 

  Antigen testing is done to diagnose viral infections, monitor and screen for certain conditions and determine whether a donor is a good match for a transplant.
• An antigen is any kind of chemical marker — like a protein or string of amino acids — that your immune system can recognise. Antigens are usually proteins or sugars (polysaccharides) found on the outside of things like cells or viruses. Each has a unique shape that your immune system reads like a nametag to know whether it belongs in your body.
• Antigen can originate either from within the body "self-protein" or "self- antigens" or from the external environment "non-self“.

  The antigens on your own cells are known as self-antigens, while those that do not originate in your body are called non-self-antigens. Self-antigens are derived from cells of the body the immune system protects.
• Antibodies is a blood protein that protect when an unwanted substance enters the body. 

  Produced by your immune system, antibodies bind to these unwanted substances in order, to eliminate them from your system… chemically binding. 

  Another word for antibody is immunoglobulin