QS Study


An antigen is a high molecular wt foreign substance when introduced into a suitable route in a suitable host produce antibody with which it reacts specifically. It is a toxin or other foreign substance which induces an immune response in the body, especially the production of antibodies. The body combats an antigen with the production of an antibody.

Antigens can be bacteria, viruses, or fungi that source infection and disease. It is regarded as a threat by the immune system and is capable of stimulating an immune response. They can also be substances, called allergens, which bring on an allergic reaction. Common allergens include dirt, pollen, animal dander, bee stings, or definite foods. Blood transfusions containing antigens mismatched with those in the body’s own blood will arouse the production of antibodies, which can cause severe, potentially life-threatening reactions.

Criteria for an antigen

  1. It should be a macromolecule, m,wt more than 1 x 104.
  2. It should be protein or polysaccharide.
  3. It should be foreign to the host.
  4. It is specific in action.

When an antigen enters the body, the immune system produces antibodies against it.