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WHAT IS ALLERGY?
An allergy is an
inappropriate or exaggerated reaction of the immune system to substances
that cause no symptoms in most people. An Allergic individual have an
abnormal reaction or increased sensitivity to certain substances and
produce symptoms when exposed to these substances, which are harmless to
non-allergic people.
The main reason for this is that allergic people make a special type of
antibody called Immunoglobulin E (IgE), which can react with
environmental substances in a harmful way. These substances are called
allergens.
The reaction between allergens and IgE antibodies causes the release of
substances such as histamine, which produce allergic symptoms in the
skin, the nose, the eyes, the chest, etc.
The most common allergens are animal dander, pollens, house dust, house
dust mites, molds, some drugs and many foodstuffs, especially fish,
eggs, milk and nuts. Bee and wasp stings may cause allergic reactions,
with fatal results in rare cases. Additionally, feathers, wool, dyes,
cosmetics and perfumes may act as allergens.
COMMON ALLERGIES
Allergic reactions or diseases may involve any part of the body; the
most frequently involved are the nose and chest with resultant symptoms
of hay fever, rhinitis or asthma, respectively. The skin and eyes also
commonly show allergic symptoms. Anaphylactic shock is a severe allergy,
which affects many organs at the same time causing a rapid decrease in
blood pressure, fainting and, occasionally, death. Such a reaction,
though, is rare.
Hay Fever
If you suffer from hay fever, the pollens of grasses, weeds and trees
are the main causes of this type of allergy, although mold spores can
also cause the symptoms.
The lining of the nose becomes swollen and exudes a runny discharge.
Spells of sneezing and itchiness of the throat and palate also occur and
the eyes may be similarly affected.
Depending on where you live and the pollinating periods, attacks may
occur in spring, summer or autumn. Contact lense wearing time may
decrease due these symptoms
In perennial allergic rhinitis, the symptoms are similar to hay fever
but appear all the year round. This condition is caused by non-seasonal
allergens such as house dust components and certain molds.
Conjunctivitis
You are more likely to suffer
from this allergic condition of the eyes as an adult. Allergic
conjunctivitis is often associated with allergic rhinitis. A general
complaint is of itchiness of the eyes, which are rubbed frequently.
Asthma If you have asthma, you can suffer from attacks that obstruct the
flow of air to the lungs. Breathing becomes difficult and forced
breathing becomes necessary. A wheezing sound can appear, due to the
rush of air through your narrowed airways. At the same time, a
troublesome cough can develop. Asthma may begin at any age and, if
neglected, tends to recur and become chronic.
Eczema
If you suffer from eczema,
your skin can become irritated and develop rashes that can be either wet
or dry and occasionally chapped. The reactions are often accompanied by
severe itching. The cause is often not clear, but is frequently seen in
children of families with a history of allergic diseases. The eczema may
start during the first year of life, on the face. Later, it is often
seen on the inside of the elbows and backs of knees, on the neck, on the
ankles, on the wrists and on the back of the hands. It is possible for
eczema to become secondarily infected with skin bacteria, especially if
there is much broken skin due to scratching.
Urticaria, Hives (Nettlerash)
This reaction appears very
suddenly. Your skin becomes warm, reddish and itching. The symptoms may
last either for a couple of hours or up to a whole day. Blotches may
appear as raised wheals and vary in size from smaller than a mosquito
bite to several inches in diameter. In 95% of hives, the cause is
unknown.
Contact Dermatitis
With contact dermatitis, your
symptoms will be similar to those of the eczema previously described,
but this reaction is of another type. The cause is direct contact with
different substances, such as:
nickel (in coins, stainless steel, clasps, jewelry)
rubber products (in gloves, boots, waistbands)
chromium (in cement, leather)
latex
preservatives (in creams, ointments and cosmetics)
This condition, unlike those listed above, is not due to the production
of IgE antibodies, but is due to a different kind of immune reaction. It
is usually due to increased sensitivity to a substance that a particular
body part contacts.
Food Allergy
The stomach and the digestive
system are also frequent targets for allergic disease. Your symptoms are
caused by allergy to foods, which can result in vomiting, stomach pains,
diarrhea or constipation. Frequently, eczema and hives may be produced
after ingesting food to which you are allergic. Food allergy may also
trigger asthmatic attacks and, rarely, generalized anaphylaxis. Food
anaphylaxis is most commonly seen with ingestion of nuts and iodinated
shellfish (lobster, shrimp).
Insect Allergy
Severe allergic reactions to
bee and wasp stings are not uncommon. More people die annually in the
United States from insect sting allergy than die from snakebite. The
local toxic reaction and discomfort that usually occurs following an
insect sting is not generally considered to be allergic.
IgE mediated (allergic) reactions induce symptoms such as nettlerash (urticaria,
hives), running nose and eyes, swelling of the throat, attacks of asthma
and, in severe cases, fainting.
Swelling of an entire extremity is called a "large local reaction."
Although indicative of hypersensitivity, this type of reaction does not,
generally, proceed to anaphylaxis with future stings.
If you have had a severe insect sting or allergic reaction, your
clinician may provide you with an adrenaline containing kit for use if
you are stung. Should you be highly sensitive to bee or wasp stings, you
may become unconscious within a short space of time. Immediate action
should be taken to get you expert medical treatment, preferably at the
nearest hospital.
Occupational Allergy
The term occupational allergy
is generally used to describe episodes of allergic reactions occurring
after working with industrial dusts, vapors, gases or fumes.
Furthermore, substances like nickel (in coins), chromium (in cement),
rubber, different dyes, formaldehyde and glues may result in eczema that
occurs at the site of contact with the skin. Inhalants such as grain
dust may affect farmers.
The degree of eczema depends on the length of exposure and sensitivity
to the substance. Symptoms may show within some weeks - but it can often
take months, years, sometimes decades, before an eczema develops. Any
part of the skin may become affected, but the most frequent sites are
the hands, arms and the face, because these tend to be the least
protected parts of the body. Occupational allergy may also present with
pulmonary or upper respiratory treatments. Workers will often get better
over the weekend, on business trips, or vacation and symptoms will often
recur after return to the same work environment.
ALLERGIC MECHANISMS
Allergy is an unusual reaction or sensitivity to substances that do not
bother most people.
IgE Mediated Allergy
Following exposure to common environmental allergens, the allergic
individual produces a special type of antibody, called Immunoglobulin E,
or IgE. The healthy individual has a very low level of IgE in the blood,
while those with certain allergic conditions such as hay fever, allergic
asthma and some forms of eczema have high IgE levels. People with eczema
have especially high blood levels of IgE.
In the human body, certain cells called mast cells and basophils are
involved in allergic reactions. IgE, produced as a result of repeated
allergenic stimulation, attaches to the surface of these cells and
subsequent binding of the allergen punctures the cell wall, leading to
the release of different substances.
These substances cause a build-up of fluid in the tissue, and
contraction of the smooth muscles. Depending on the route of entry of
the allergen and where the reaction takes place, different symptoms will
occur. If the reaction takes place in the nose and eyes, hay fever will
result - while asthma is the result if the chest is affected. Eczema
appears when the skin is affected.
Who Becomes Allergic?
Anyone can develop an allergy,
but the probability is increased if one or both parents suffer from some
kind of allergic condition. Indeed, the presence of another allergic
individual in the family is the strongest factor for predicting allergy
in a child. It must be noted, though, that even when both parents are
affected, a child may not be. Conversely, allergic children are born to
normal parents and in such cases other factors, such as infection, may
be responsible for the development of the allergy. Repeated exposure to
a substance is required before the body can recognize it as foreign and
mount an allergic response.
DIAGNOSIS
It is essential for successful treatment that the allergens
responsible for the symptoms are accurately identified. There are
different ways to arrive at a diagnosis. The case history is extremely
important in all allergy investigations. Based on what the patient tells
about his/her symptoms, the doctor decides what tests, if any, should be
carried out.
Laboratory Tests
IgE plays an important role in allergic rhinitis, allergic asthma and in
some forms of eczema. Detecting and accurately measuring the amount of
IgE may be of great importance when diagnosing allergies.
Because of the limitations and disadvantages associated with skin and
provocation tests, there has been a need for more convenient and
reliable methods. Today, there are laboratory tests available that
accurately measure IgE, and a small blood sample is sufficient for
allergy testing. These tests measure either the total amount of IgE in
the blood, which indicates if your symptoms are of allergic origin or
specific IgE, which tells the doctor which allergens are causing the
trouble. Another allergy blood test is called RAST (radioimmunoabsorbent
test). These blood tests are significant primarily if the identified
substances cause patient symptoms. RAST is especially helpful in very
young children.
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IgE Mediated Allergy
Following exposure to common environmental allergens, the allergic
individual produces a special type of antibody, called Immunoglobulin E,
or IgE. The healthy individual has a very low level of IgE in the blood,
while those with certain allergic conditions such as hay fever, allergic
asthma and some forms of eczema have high IgE levels. People with eczema
have especially high blood levels of IgE.
In the human body, certain cells called mast cells and basophils are
involved in allergic reactions. IgE, produced as a result of repeated
allergenic stimulation, attaches to the surface of these cells and
subsequent binding of the allergen punctures the cell wall, leading to
the release of different substances.
These substances cause a build-up of fluid in the tissue, and
contraction of the smooth muscles. Depending on the route of entry of
the allergen and where the reaction takes place, different symptoms will
occur. If the reaction takes place in the nose and eyes, hay fever will
result - while asthma is the result if the chest is affected. Eczema
appears when the skin is affected.
The Mechanism of an
Allergic Reaction
There are three stages to the allergic response: In the first stage, the
immune system encounters the foreign substance and identifies it as an
invader. It then primes the immune system to recognize this invader as
an enemy that needs to be destroyed in future encounters. This stage is
known as sensitization. The subsequent stages are mast cell activation,
and prolonged immune activation.
STAGE 1- SENSITIZATION
The first time an allergen meets the immune system, no allergic
reaction occurs. Instead, the immune system prepares itself for future
encounters with the allergen. Scavenger cells called macrophages
surround and break up the invading allergen. The macrophages then
display the allergen fragments on their cell walls to specialized white
blood cells, called T lymphocytes, which are the main orchestraters of
the body's immune reaction. The T cells secrete a signaling chemical
called interleukin-4, which activates other white blood cells known as B
lymphocytes. These cells secrete antibodies specific for that particular
allergen. These antibodies, called immunoglobulin E (IgE) receptors, are
attached to cells in the immune system, called mast cells and basophils.
Individuals prone to allergies are known to have abnormally high levels
of IgE antibodies.
STAGE 2- MAST CELL ACTIVATION
Stage 2, or mast cell activation, represents a later encounter
between the allergen and the immune system and usually occurs within
minutes after the second exposure to an allergen. IgE antibodies on mast
cells, constructed during the sensitization phase, recognize the
allergen and bind to the invader. Once the allergen is bound to the
receptor, granules in the mast cells release their contents.
These contents, or mediators, are substances such as histamine,
platelet-activating factor, prostaglandins, and leukotrienes. Mediators
are what actually trigger the allergy attack. Histamine stimulates mucus
production and causes redness, swelling, and inflammation.
Prostaglandins constrict airways and enlarge blood vessels.
STAGE 3- LATE PHASE
INFLAMMATORY RESPONSE
In Stage 3 tissue mast cells and neighboring cells produce chemical
messengers that signal circulating basophils, eosinophils, and other
cells to migrate into that tissue, to help fight the foreign material.
These recruited immune cells secrete chemicals of their own that sustain
inflammation, cause tissue damage, and recruit yet more immune cells.
This phase occurs several hours after exposure and can last for hours
and even days.
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Allergy Screen - Basic
Molds |
This Panel is a quantitative
Allergen-Specific IgE Test for the following molds
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 Cladosporium herbarum
Aspergillus fumigatus
Mucor racemosus
Candida albicans
Alternaria tenuis
Helminthosporium spp.
Fusarium moniliforme
Pullularia pullulans
Phoma betae
Epicoccum purpurascens
Stemphylium solani
Hormodendrum hordei
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