Niels Kaj Jerne

Niels Kaj Jerne was a Danish immunologist who developed three influential theoretical frameworks that shaped modern understanding of how the immune system works. His earliest major idea, the natural selection theory of antibody formation, proposed that the body already carries a wide diversity of antibodies before any infection occurs and that an invading antigen simply selects and amplifies the matching ones, rather than the immune system designing a new antibody in direct response to each new threat, an idea that fed into Frank Macfarlane Burnet's later, more complete clonal selection theory. Jerne also proposed that the immune system's tolerance of the body's own tissues is actively learned during a developmental period in the thymus gland, and in a further theoretical step he introduced what became known as immune network theory, describing the immune system as a continuously self-regulating web in which antibodies react not only to foreign antigens but to one another, maintaining a dynamic equilibrium that shifts when a genuine foreign antigen disrupts it. Jerne was awarded the 1984 Nobel Prize in Physiology or Medicine, shared with Georges Kohler and Cesar Milstein, for theories concerning the specificity in development and control of the immune system, and he served as director of the Basel Institute for Immunology, an institution he helped found.