The Concept of Immunodiagnosis

The idea that specific immune responses could be used for diagnosis sprang from the studies of infection carried out in the last decades of the 19^th century during the golden age of microbiology. Building on the demonstration by Roux and Yersin that some microorganisms such as the bacilli of diphtheria and tetanus produce their pathologic effects through the production of a soluble toxin, Von Behring and Katasato in 1890 showed that animals given sublethal doses of a toxin develop resistance to its effects. Using transfer experiments, they showed that the basis of this acquired resistance was found in the serum. These neutralizing antitoxins were disease specific and could be used for treatment of the particular disorder. Soon other factors were identified in the serum in response to infection in the form of lysins by Pfeiffer, agglutinins by Gruber and Durham, and precipitation by Kraus. Later Widal and others propounded the concept that the presence or increase of antibodies could provide a tool for diagnosis. The rationale for today's widespread application of antibody-based diagnosis derives from that simple idea.