In 1976, Danish immunologist Niels K. Jerne made an observation that has led to a fundamental change in the concept of the immune system. Jerne found that the antigen-binding region of an antibody is identified as 'foreign' by the immune system that has produced it. Accordingly, an immune response is triggered and anti-idiotypic antibodies are produced to target the original antibodies. In addition, these anti-idiotypic antibodies may further provoke the production of a third and even fourth level of anti-idiotypic antibodies; this network keeps antibody levels in balance, and is also how the immune system shuts itself off after successfully fighting an infection.
