Allergy | Research & Encyclopedia Articles

Allergy

An allergy is a reaction to a foreign substance by a person sensitive to that substance. Allergies are part of the body's immune mechanisms. They are triggered when an antigen--a substance foreign to the body--enters or contacts the body, which stimulates the production of antibodies. When antigens and antibodies interact, they cause the release of active substances into the body fluids. These substances, the most common of which is histamine, cause allergic responses such as muscle contraction, swelling, itching, coughing, and difficulty in breathing. Substances that act as antigens--like eggs, roses, or pet hair--are usually harmless to nonallergic persons.

Allergic reactions have been noted since ancient times, but recognition that they were triggered by external agents did not begin to develop until the sixteenth century. Leonardo Botallo (1530-1575) described the "rose cold" or "rose fever" in 1565, a condition involving asthma and common cold symptoms caused by contact with roses. The famed Italian physician Girolamo Cardano (1501-1576) treated the Archbishop of Edinburgh, John Hamilton, for asthma in 1552 by instructing the clergyman to remove all feathers from his bedding. In 1607 Johannes van Helmont described a case of bronchial asthma, and in 1697 Sir John Floyer (1620-1689) noted that environmental pollution such as smoke made the condition worse. Skin testing for allergic reactivity, a common diagnostic tool today, was used by Pierre Borel in 1656; he applied some egg to a patient's skin to demonstrate the man's sensitivity to eggs.

During the nineteenth century, understanding of the immune system and allergic response grew considerably. In 1819 a London physician, John Bostock (1773-1846), described a seasonal nose infection that was dubbed "Bostock's summer catarrh," better known in later years as hay fever. John Elliotson (1791-1868) suggested in 1831 that the catarrh was caused by grass and weed pollen. This concept was confirmed in 1835 by W. P. Kirkman, a physician who suffered from asthma; when Kirkman sniffed some pollen-laden greenhouse grass in mid-winter, he had a severe asthmatic reaction. The English scientist Charles Blackley had a similar unseasonal asthma attack caused by a vase of dried grasses during the winter of 1871. When he scratched pollen into his skin, the resulting inflammation proved that pollen could cause an allergic reaction. For his asthmatic patients, Blackley suggested spending the summer pollen season aboard a boat or on a peninsula. Blackley published his findings in 1872; Morrill Wyman (1812-1903) of Harvard University published similar, independent results in 1873. Around the same time, Henry Salter concluded that the causes of asthma and hay fever could be identical, both conditions being triggered by contact with hay and various domestic animals.

The mechanism of the allergic reaction was unraveled during the twentieth century. In 1902 Charles Richet, a French physiologist, discovered the extreme allergic reaction called anaphylaxis, in which an injection of a substance produced such intense sensitivity that a second, mild injection could cause death. Maurice Arthus found, in 1903, that second injections could cause severe local inflammation. The same year, German physician Wilhelm Dunbar proved that reaction to pollen was not caused by physical irritation; he theorized that toxin played a role. Austrian pediatrician Clemens von Pirquet (1874-1929) introduced the term allergy in 1906 to describe these sensitive reactions.

In 1907 Henry Dale (1875-1968) began studying an ergot extract that had been shown to have a powerful stimulant effect on a cat's uterus. By 1910 Dale had isolated the new stimulant, which he eventually called histamine. Both Dale and Patrick Playfair Laidlaw (1881-1940) found that histamine created effects similar to the shock response described by Richet in anaphylaxis. Histamine did not attract much attention until 1926, when Dale and his colleagues found substantial amounts of it in liver extract and then also in gastric and pituitary extracts. Once researchers became aware that histamine existed in the body and produced effects such as dilation of the blood vessels, they began to study the substance closely. Investigators found that histamine, or similar substances, were released into the body during the antigen-antibody reaction, and that these substances seemed to cause the symptoms of allergic reaction. The fact that injured cells do in fact produce histamine was demonstrated by Thomas Lewis (1881-1945) of England in 1932, by Wilhelm Feldberg of Germany, and Carl Draystedt of the United States. Lewis and William Duke (1882-1946) both showed that histamine caused allergic reactions to heat, cold, and sunlight. An American physician, Charles Cole, discovered how to test for the presence of histamines.

Now that histamines were recognized as the triggering agents for allergic reactions, efforts were made to find antagonists. Success was achieved by Swiss-Italian physiologist Daniele Bovet, who synthesized the first antihistamine in 1937. Pharmacology researchers soon developed a large number of synthetic antihistamines, which became extremely popular among allergy victims for relief of their symptoms.

A recent phenomenon associated with allergies is multiple chemical sensitivity (MCS), sometimes called "total allergy sensitivity." In people who claim to have MCS, symptoms may range from headaches to sinus problems to trouble sleeping. Like traditional allergies, the causes are thought to be environmental, including chemical and non-chemical agents, like electromagnetic waves. However, whether or not MCS is really an accepted disorder has been under hot debate. While most patients and some physicians believe that MCS is a true "allergic" response, others claim that MCS is primarily psychological in nature.