Allergies 1906 – An Overreaction of the Immune System

Allergic diseases have been known since ancient times. 

• Around AD 900, Persian physician Al-Razi, also known as Rhazes, described seasonal rhinitis, a condition (nasal inflammation) triggered by the smell of roses. 
• In 1902, French physiologists Charles Richet and Paul Portier observed that dogs died on a second exposure to sea-anemone toxins and discussed anaphylaxis (an acute allergic reaction that can lead to multiple organ failure and death). 
• In 1906, Austrian paediatrician Clemens von Pirquet combined sea-anemone experiments carried out with Hungarian paediatrician Béla Schick with his own studies of "serum sickness". In particular, they noticed that children vaccinated against common infectious diseases showed faster and more severe reactions when exposed to the vaccine a second time. 

Pirquet used a term for what he believed was an abnormal response of an overactive or hypersensitive immune system: "allergy".

Consider the modern explanation of a person's first encounter with a potential allergen, such as flower pollen or bee venom:

• In certain individuals, various white blood cells may begin to overreact. In particular, a TH2 lymphocyte may produce interleukin-4 (a protein signalling molecule), encouraging excessive production by B cells.
• This may lead to overproduction of IgE antibodies that bind to mast cells and basophils. 
• At this point, the IgE-coated cells become sensitised to the particular allergen and "remember" it. 
• If the person encounters the allergen again, activated mast cells and basophils release histamine and other inflammatory chemicals into the surrounding tissues.
• This causes itching, rashes, hives and possible anaphylaxis, which can sometimes be treated with antihistamines, steroids or epinephrine injections.

The likelihood of having allergies is higher in developed countries. Allergies are often inherited from parents. According to one theory, The relative sterility of modern urban environments cannot keep the immune system "busy" because exposure to pathogens is insufficient.

Allergies are also less common in children from large families, probably because of greater exposure to microbes and parasites. This has sometimes been associated with the presence of organisms capable of beneficially suppressing the immune system.

Description of the article image: A colourised electron microscope image containing pollen from common plants such as sunflower, morning glory, hollyhock, lily, primrose and horsetail (Dartmouth Electron Microscope Facility).

Historical figures mentioned in the article: Abu Bakr Muhammad ibn Zakariya al-Razi (865–925), Charles Richet (1850–1935), Paul Portier (1866–1962), Clemens Peter Freiherr von Pirquet (1874–1929), Béla Schick (1877–1967) 

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