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THE FASCINATING BIOLOGY OF ALLERGIES
A very big chunk of the worlds population suffers from some kind of allergy. Tremendous amounts of scientific research and studies have been made to understand the simple-looking concept of an allergy. Is it really that simple?
What Is An Allergy?
An allergy is an abnormal reaction of the immune system of our body to a foreign substance. This reaction may or may not be immediate. The immune system needs time to recognize and remember the allergen(Any substance that causes the body to have an allergic reaction).
As the body becomes sensitive to the substance, the immune system starts making antibodies to attack it. This process is called sensitization. It may take a few days or even a few years.
The Causes Of An Allergy
An allergy can literally be caused by anything under the Sun. However, the most common forms of an allergies are:
- Insect stings
- Nuts (Peanuts, tree nuts etc.)
- Certain medications
Allergies are not common to everyone. Some people’s bodies overreact to certain substances which in turn causes an allergic reaction.
Fighting Against Allergies
In our body, substances called immunoglobulins(The antibodies created by our immune system) fight against foreign contaminants, that mainly consist of pathogens. These immunoglobulins are produced by Plasma B-cells of our body which are a type of B-lymphocyte which further are a type of Lymphocytes(Type of White Blood Cells).
Immunoglobulins are basically proteins (Gamma globulins). They are represented by the symbol ‘Ig’. They are of five types:
- Ig-G : These are the smallest immunoglobulins
- Ig-M : These are the largest immunoglobulins. Whenever there is a foreign contaminant in our body, these are the ones released first.
- Ig-E : The immunoglobulin related to allergies
Substances which stimulate these antibodies are called antigens and substances which stimulate allergies are called allergens. Plasma B-cells in the body analyse these antigens and transfer information about them to other cells that produce the antibodies. These antibodies attack a specific antigen and have little or no effect on other antigens. The antibodies remain in the bloodstream after the antigen is removed.
No one is born with Ig-E antibodies in their body. When first exposed to an allergen, it takes about 10 days before the Ig-E is developed. By this time the allergen is gone so no allergic reaction occurs. A second exposure to the allergen causes the allergic reaction. It takes repeated exposures to allergens for people to develop an allergy.
Ig-E is not a single protein structure (molecule), but a class of molecules each having a slightly different structure. Each molecule reacts with a specific antigen. This is why people have specific allergies. For example, the Ig-E that reacts with pollen is not the same form of Ig-E that reacts with the antigen from a nut.
Ig-E is present in the body in extremely small amounts, about 1 part per million in blood plasma. People who have allergic reactions have more Ig-E present than normal. For example, a person with allergic asthma has six times as much Ig-E as one with non-allergic asthma.
Functioning of Ig-e
The tail of an Ig-E molecule (which is Y shaped) attaches itself to certain cells in the body known as mast cells. A single mast cell can bind more than 100,000 Ig-E molecules. Within the mast cells are granules that contain chemicals which are known as mediators. When an allergen combines with an Ig-E molecule on the mast cell, the mediators are released.
Although numerous different chemicals are present as mediators, only two of them appear to play a role in human allergies. These are known as histamine and slow reacting substance (also known as SRA-A). Of these two, histamine is the chemical responsible for the side reactions we associate with allergies such as itching, swelling, and runny- nose.
These allergens can enter our body in four main ways:
- By inhaling
- By ingesting (eating or drinking)
- By touching
- By injection (insect bites)
How does Histamine works?
Histamine, formed by the breakdown of a common amino acid known as histidine, is found in high concentrations in the granules in mast cells, and is released as granules which move to the outer edge of the mast cell. They discharge the histamine through a temporary gap in the plasma membrane. In immediate reactions, histamine can account for many, if not all of the symptoms associated with an allergic reaction.
Histamine causes dilation of the blood vessels and increases the ability of blood fluids to leak out of capillaries. These fluids are responsible for the swelling of tissues. It also causes contraction and swelling of smooth muscles, stimulates the production of saliva, tears and secretes mucus. It can also cause a large drop in blood pressure and narrowing of airways, producing a condition known as anaphylactic shock, which can even lead to death.
Symptoms Of An Allergy
Common symptoms of an allergic reaction include:
- Sneezing and an itchy, runny or blocked nose (allergic rhinitis)
- Itchy, red, watering eyes (conjunctivitis)
- Wheezing, chest tightness, shortness of breath and a cough
- A raised, itchy, red rash (hives)
- Swollen lips, tongue, eyes or face
- Tummy pain, feeling sick, vomiting or diarrhoea
- Dry, red and cracked skin
- Antihistamines – Antihistamines can help to treat most minor allergic reactions regardless of the cause. These drugs reduce the body’s production of histamine, which reduces all symptoms, including sneezing, watering eyes, and skin reactions. Antihistamines come in several forms, usually to help deliver the medication closer to the source of the reaction or make it easier to consume, such as:
- Oral pills
- Dissolvable tablets
- Eye drops
- Nasal decongestants – Nasal decongestant pills, liquids, and sprays can also help reduce stuffy, swollen sinuses and related symptoms, such as a sore throat or coughing.
- Avoid the allergen – The best way to treat and prevent allergic reactions is to know what triggers the reaction and stay away from it, especially food allergens.
When this is not possible or realistic, using antihistamines or decongestants when in contact with allergens can help to treat the symptoms.
There are other ways to treat an allergy but these are considered to be the best.
Some Interesting Facts Related To Allergies
- Aquagenic urticaria is a rash caused by contact with water. (i.e., allergy to water) There are just 32 people on the planet affected by this allergy. The water source responsible for inducing the urticaria can be fresh, salt or chlorinated water.
- Allergy to pollen is the most common type of allergy
- Allergies can also kill a person by a process called anaphylaxis. It basically is a more severe case of allergy and can be reversed by taking epinephrine.
- There is a type of allergy in which the patient becomes allergic to sunlight. This is known as polymorphic light eruption, or PLE.
- Believe it or not, there are some who suffer from allergic reactions just from handling loose change. Developing an allergic rash on your hands after handling coins is a sign that you’re allergic to nickel sulphate.
- There are people who suffer from allergy to human touch known as dermographism. Those who suffer from dermographism (meaning “skin writing”) can actually write their own names on their skin as their touch causes a physical allergic reaction.
- There are people who are allergic to clothes. Clothing dermatitis can be caused by a bunch of things. While some people are allergic to wool or cotton itself, most clothing allergies are a result of synthetic things like rubber materials, formaldehyde finishing resins, chemical additives, dyes, glues, and tanning agents used in processing the fabric.
Author – Riddhi Bhargava (firstname.lastname@example.org)
Editor – Kulvir Chavda
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