What is the History of Immunology

𝗛𝗶𝘀𝘁𝗼𝗿𝘆 𝗼𝗳 𝗶𝗺𝗺𝘂𝗻𝗼𝗹𝗼𝗴𝘆

Immunology started in the last quarter of the nineteenth century with two major discoveries. The first of these was Elias Metchnikff's (1845–1916) identification of phagocytosis cells, which engulf and destroy invading pathogens (1). This laid the basis for innate immunity

Although most historical accounts credit Edward Jenner for the development of the first immunization process, a previous similar procedure had become established in China by 1700. Immunity to smallpox was conferred by inserting the dried exudate of smallpox pustules into the nose. This technique for the transfer of smallpox, as a form of limited infection, traveled to the west from China along the traditional trade routes where it spread throughout Europe. Hearing of this practice, the Royal family of England had their children inoculated against the disease in 1721, but the practice aroused severe opposition as physicians felt it was far too risky.

In 1798, Edward Jenner, noticed that milkmaids were protected from smallpox infected with cowpox. It was not his intention to make medical history, as his interests were mostly scholarly and involved the transfer of infections from one species to another, especially from animals to humans. However, Jenner's work led him to the conclusion, that inoculation with cowpox (a bovine analogue of smallpox) could confer immunity to smallpox. Thus, the concept of vaccination was initiated. Jenner's ideas first made him a medical as well as a social pariah, as they were in opposition to both the church and popular beliefs. Because his method was much safer, however, the use of vaccinations gradually became widely accepted and most European countries had some form of compulsory program within fifty years of Jenner's discovery.

The idea that a pathogenic organism caused disease was not fully realized until certain technological advances had occurred. That these organisms were the causative agent of disease not recognized until Louis Pasteur germ theory of disease his original interests were in fermentation in wine and beer, and he was the first to isolate the organisms that caused the fermentation process. Pasteur's work eventually led him to the development of pasteurization (heating) as a means of halting fermentation. While working with silk worms and anthrax, he was able to demonstrate that the same method for transferring the fermentation process also worked in transmitting disease from infected animals to unaffected animals. Finally, in 1878, Pasteur accidentally used an attenuated (weakened) chicken cholera culture and realized, when he repeated the experiment using a fresh culture, that the weakened form protected the chickens from the virulent form of the disease. Pasteur went on to develop an attenuated vaccine against rabies and swine erysipelas.

Pasteur was not the only proponent of the germ theory of disease. His chief competitor was Robert Koch. Koch was the first to isolate the anthrax microbe and, unaware of Pasteur's work, he was able to show that it caused the disease. Then in 1882, Koch was able to demonstrate that the germ theory of disease applied to human ailments as well as animals, when he isolated the microbe that caused tuberculosis. His "Koch's postulates" are still used to identify infective organisms.

Much of the basis for modern medicine, as well as the field of immunology, can be traced back to these two scientists, but the two major questions still to be answered were how did infection cause the degradation of tissue, and how did vaccines work? The first question was addressed in 1881 by Emile Roux and Alexander Yersin when they isolated a soluble toxin from diphtheria cultures. Later, Emil von Behring were able to demonstrate passive immunity when they took serum from animals infected with diphtheria and injected into healthy animals. How. Ehrlich hypothesized that these antibodies were specialized molecular structures with specific receptor sites that fit each pathogen like a lock and key. In addition, sometime later, he realized that this powerful effector mechanism, used in host defense would, if turned against the host, cause severe tissue damage.

Although extremely valuable, his work still left a large gap in understanding how the immune system fights a pathogenic challenge. Metchnikoff postulated that vertebrates could operate to remove pathogens. 

The clarification of the immune response and the science of immunology did not progress in a systematic or chronological order. Nonetheless, once scientists had a basic understanding of the cellular and humoral branches of the immune system, what remained was the identification of the various components of this intricate system, and the mechanisms of their interactions. This could not have been accomplished without the concomitant development of molecular biology and genetics.

See also Antibody and antigen; B cells or B lymphocytes; Germ theory of disease; History of the development of antibiotics; History of public health; Immunity, active, passive and delayed; Immunity, cell mediated; Immunity, humoral regulation; Infection and resistance; T cells or T-lymphocytes