The first Nobel Prize in Physiology or Medicine acknowledged both the development of a scientific concept that concerned the way in which the immune system can fight certain infectious agents, and its successful translation into a method of keeping the illnesses they cause at bay. At the forefront of these achievements was Emil von Behring. His discovery of molecular missiles in blood led to a completely new type of therapeutic strategy, one in which immunity created through artificial means could cure life-threatening diseases.

Von Behring’s pioneering experiments were carried out on the then recently discovered bacteria that cause diphtheria and tetanus, diseases that both result from toxic substances released by the microorganisms. Working with Shibasaburo Kitasato, von Behring discovered that when animals were injected with tiny doses of weakened forms of tetanus or diphtheria bacteria, their blood extracts contained chemicals released in response, which rendered the pathogens’ toxins harmless. Naming these chemical agents “antitoxins”, von Behring and Erich Wernicke showed that transferring antitoxin-containing blood serum into animals infected with the fully virulent versions of diphtheria bacteria cured the recipients of any symptoms, and prevented death. What was true for animals was found to be true for humans; transferring such immune serum into children treated their symptoms of diphtheria, and stopped them dying of the disease.

After techniques were developed that could produce high-quality levels of antitoxin-containing blood extracts on an industrial scale, von Behring’s method of treatment, passive serum therapy, became an essential remedy for diphtheria, saving many thousands of lives every year. Thanks to his discoveries, these antitoxins, later called antibodies, also sparked a new line of scientific enquiry. Researchers rushed to seek other circumstances under which neutralizing antibody molecules are created to allow a host to acquire immunity to pathogenic organisms.