The immune network theory is a theory of how the adaptive immune system works, that has been developed since 1974 mainly by Niels Jerne and Geoffrey W. Hoffmann. The theory states that the immune system is an interacting network of lymphocytes and molecules that have variable (V) regions. These V regions bind not only to things that are foreign to the vertebrate, but also to other V regions within the system. The immune system is therefore seen as a network, with the components connected to each other by V-V interactions. It has been suggested that the phenomena that the theory describes in terms of networks are also explained by clonal selection theory. The scope of the symmetrical network theory developed by Hoffmann includes the phenomena of low dose and high dose tolerance, first reported for a single antigen by Avrion Mitchison, and confirmed by Geoffrey Shellam and Sir Gustav Nossal, the helper and suppressor roles of T cells, the role of non-specific accessory cells in immune responses, and the very important phenomenon called I-J. Jerne was awarded the Nobel Prize for Medicine or Physiology in 1984 partly for his work towards the clonal selection theory, as well as his proposal of the immune network concept. The immune network theory has also inspired a subfield of optimization algorithms similar to artificial neural networks. The symmetrical immune network theory Heinz Kohler was involved in early idiotypic network research and was the first to suggest that idiotypic network interactions are symmetrical. He developed a detailed immune network theory based on symmetrical stimulatory, inhibitory and killing interactions. It offers a framework for understanding a large number of immunological phenomena based on a small number of postulates. The theory involves roles for B cells that make antibodies, T cells that regulate the production of antibodies by B cells, and non-specific accessory cells (A cells). Antibodies called IgG have two V regions and a molecular weight of 150,000. A central role in the theory is played by specific T cell factors, which have a molecular weight of approximately 50,000, and are postulated in the theory to have only one V region. Hoffmann has proposed that for brevity specific T cell factors should be called tabs. Tabs are able to exert a powerful suppressive effect on the production of IgG antibodies in response to foreign substances (antigens), as was demonstrated rigorously by Takemori and Tada. Hoffmann and