The INDIVIDUALIST

A Wiki about biochemical individuality

Immunology

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Description

The word allergy means 'altered working'. It was coined at the beginning of the 20th century to describe the fact that when dogs were innoculated with proteins from another animal they had altered reactions when they came into contact with that protein again. These reactions were harmful, and the dogs died often during the "allergic reaction".

Allergies are the result of your immune system overreacting to normally harmless substances in our environment These substances have been given the generic name 'allergen' which is a substance that causes no harm to most people but triggers an array of symptoms in sensitive individuals ranging from mildly annoying to life-threatening. Common allergens include dust mites, pollen, foods such as peanuts, wheat? and strawberries, and drugs such as penicillin. Allergies are pervasive in our society. According to the National Institute of Allergy and Infectious Diseases (NIAID), people with allergies spend more than $5 billion annually on doctors' visits, allergy shots and prescription medications.

An allergic reaction is basically the immune system getting out-of-control. In addition to attacking true enemies such as viruses and bacteria, the immune system of an allergic person also springs to action when an allergen is present. When an allergic person is exposed to an allergen their B lymphocytes produce a special class of antibodies known as Immunoglobulin E, or IgE. These IgE molecules can readily bind to the allergen that caused their production - they are "specific" for the original allergen. Specific IgE molecules travel through the blood and attach to receptors on the surface of mast cells. Different IgE antibodies are produced for each type of allergen, whether it's latex, pet dander, oak pollen or ragweed pollen. Once on the mast cell surface, allergen-specific IgE can remain for weeks or even months, always ready to bind to the original allergen. The next time the allergen enters the body, the allergic cascade begins and eventually results in the release of histamines from the mast cell. Different chemicals are produced and released depending on the allergen. These chemicals target certain areas of the body, producing a wide range of symptoms in just minutes or up to one hour. As annoying, or even life-threatening as they are allergies do serve something of a purpose - they are an attempt by the body to wash away the offending allergen.

Symptoms vary in severity and affect different parts of the body. Some allergens that affect the respiratory system such as pollen, dust mites and mold cause watery eyes and coldlike sneezing, coughing and postnasal drip. Allergens that affect areas lower in the upper respiratory system can make it difficult to breathe, and cause asthma. Food allergens strike the digestive system, causing symptoms such as nausea, vomiting, abdominal cramps and diarrhea.

People seem to inherit allergies, most often from their mothers. At least 3 genes are believed to be responsible for allergy, but only one has been identified. This gene produces interleukin 4 (IL-4) a growth factor that is required for production of IgE. Overproduction of IL-4 leads to more IgE which leads to allergy. One theory postulates that the allergic response is a defensive reaction of the immune system against certain innocuous substances that the body mistakes for harmful parasites. This is probably true, IgE is found to increase greatly in response to parasite infection. The eosinophils kill parasites (mainly worms) in conjunction with IgE, and one of the classic signs of a child with parasites is an itchy nose and watery eyes -the result of the immune system trying to kill the parasite and meanwhile liberating enough IgE to mimic the symptoms of allergy. Non-Caucasians tend to have higher levels of IgE than Caucasians, and males tend to have higher levels than females. Like the anti-blood type antibodies, the levels of IgE tend to drop as we age, which perhaps explains why some people grow out of childhood allergies.

Lectins and Allergy

Most lectins given orally are immunogenic. Pooled human blood typically contains high titre anti-banana lectin (BanLec-1) IgG4. Lectins can modulate IgE responses to other antigens [hG3 also does this, and there is some evidence that CD23 (the low-affinity IgE receptor) is in itself a C-type lectin.]

Dietary lectins can induce the release of IL-4 and IL-13 from human basophils. Dietary lectins are known to prime TH2 helper lymphocytes.

Most humans carry natural human antibodies to dietary lectins, including WGA, PNA, SBA. Interestingly the antibodies are still active against denatured lectins, and do not block their agglutinating properties.

Several Galectins (hG3, epsilon BP [CBP 35] bind to IgE receptors.

References

1. Cell Mol Life Sci 2002 Apr;59(4):648-64

2. Trends Glycosci.Glycotechnol.8:149-165

3. Eur J Immunol. 1999 Mar;29(3):918-27.

4. FEBS Lett 1996 Nov 18;397(2-3):139-42

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