Understanding the immune system
Self and Non-self
The heart of the immune system is the ability to distinguish between self and
non-self. Virtually every body cell carries molecules that identify it as self.
The body's immune defenses do not normally attack tissues that carry a
self-marker. When immune defenders encounter cells or organisms carrying
molecules that say "foreign," the immune troops move quickly to eliminate the
intruders. Any substance capable of triggering an immune response is called an
antigen. Antigens can be a virus, a bacterium, a fungus, or a parasite. An
antigen announces its foreignness by means of characteristic shapes called
epitopes, which protrude from its surface.
Keeping Out Foreigners
The immune system stockpiles a tremendous arsenal of cells. In order to have
room to match millions of possible foreign invaders, just a few of each type of
antibody are stored. When an antigen appears, those matched cells multiply into
a full-scale army. Antibodies belong to a family of large molecules known as
immunoglobulins. Immunoglobulins are proteins, made up of chains of amino acids.
Scientists have identified nine chemically distinct classes of human
immunoglobulins (Ig). Each type plays a different role in the immune defense
strategy. IgE, which under normally occurs only in trace amounts, is the villain
in allergic reactions. Each IgE antibody is specific; one reacts against oak
pollen, another against ragweed.
OOPS! False Alarm
The first time an allergy-prone person is exposed to an allergen, he or she
makes large amounts of the corresponding IgE antibody. These IgE molecules
attach to the surfaces of cells in the body. When an IgE antibody encounters its
specific allergen, it signals the body to begin powerful chemical warfare. These
chemicals include histamine, heparin, eosinophils, and neutrophils.
Your Nose Knows these Symptoms…….
It’s really warfare, but to you, it may appear as one or more of the
- Sneezing often accompanied by a runny or clogged nose
- Postnasal drip
- Itching eyes, nose, or throat
- Allergic shiners (dark circles under the eyes caused by increased blood
flow near the sinuses)
- The "allergic salute" (in a child, persistent upward rubbing of the nose
that causes a crease mark on the nose)
- Watering eyes
- Conjunctivitis (inflammation of the membrane that lines the eyelids,
causing red-rimmed, swollen eyes, and crusting of the eyelids).
First The Diagnosis
People with allergy symptoms, such as the runny nose of allergic rhinitis,
may at first suspect they have a cold--but the "cold" lingers on. It is
important to see a doctor about any respiratory illness that lasts longer than a
week or two. When it appears that the symptoms are caused by an allergy, you
should see a physician who understands the diagnosis and treatment of allergies.
If the patient's medical history indicates that the symptoms recur at the same
time each year, the physician will work under the theory that a seasonal
allergen (like pollen) is involved. Properly trained specialists recognize the
patterns of potential allergens common during local seasons and the association
between these patterns and symptoms. The medical history suggests which
allergens are the likely culprits. The doctor also will examine the mucous
membranes, which often appear swollen and pale or bluish in persons with
Doctors use skin tests to determine whether a patient has IgE antibodies in
the skin that react to a specific allergen. The doctor use diluted extracts from
allergens such as dust mites, pollens, or molds commonly found in the local
area. The extract of each kind of allergen is injected under the patient's skin
or is applied to a tiny scratch or puncture made on the patient's arm or back.
Skin tests are one way of measuring the level of IgE antibody in a patient. With
a positive reaction, a small, raised, reddened area (called a wheal) with a
surrounding flush (called a flare) will appear at the test site. The size of the
wheal can give the physician an important diagnostic clue, but a positive
reaction does not prove that particular pollen is the cause of a patient's
symptoms. Although such a reaction indicates that IgE antibody to a specific
allergen is present in the skin, respiratory symptoms do not necessarily result.
Although skin testing is the most sensitive and least costly way to identify
allergies in patients, some patients such as those with widespread skin
conditions like eczema should not be tested using that method. There are other
diagnostic tests that use a blood sample from the patient to detect levels of
IgE antibody to a particular allergen. One such blood test is called the RAST (radioallergosorbent
test), which can be performed when eczema is present or if a patient has taken
medications that interferes with skin testing.
Asthma is a reversible obstructive lung disease, caused
by an increased reaction of the airways to various stimuli. It is a chronic
condition with acute exacerbations. In this country, there are approximately 28
million asthmatics; nearly one third of them (8.6 million) are children under 18
years of age. Asthma can be a life-threatening disease if not properly managed.
Asthma is characterized by excessive sensitivity of the lungs to various
stimuli. Asthma breathing problems usually happen in "episodes" or "attacks".
An asthma episode is a series of events that result in narrowed airways. These
include: swelling of the lining , tighting of muscles, and increased secretion
of mucus in the airway. The narrowed airway is responsible for the difficulty in
breathing with the familiar "wheeze".Triggers range from viral infection to
allergies, to irritating gases and particles in the air. Each person
reacts differently to the factors that may trigger asthma, including some
respiratory infections; colds; allergic reactions to pollen, mold, animal
dander, feathers, dust food1 and cockroaches; vigorous
exercise; exposure to cold air or sudden temperature change; cigarette smoke;
excitement, and stress.
Asthma therapy includes efforts to reduce the
underlying inflammation and to relieve or prevent symptomatic airway narrowing.
Such efforts should lead to reduction in airway hyperresponsiveness and help
prevent irreversible airway obstruction
The two classes of medications used to treat asthma are
bronchodilators and anti-inflammatory agents.
Mti-inflammatory agents interrupt the development
of bronchial inflammation and have a prophylactic or preventive action. They
may also modulate or terminate ongoing inflammatory reaction in the airways.
These agents include corticosteriods, cromolyn sodium or cromolyn-like
compounds, and other anti-inflammatory compounds.
- Bronchodilators act principally to dilate the airways by relaxing
bronchial smooth muscle. They include bet~adrenergic agonists, methylxanthines,
Asthma is the leading serious chronic illness among
children. Most children have mild to moderate problems and their
illness can be controlled by treatment at home or in the doctor's office. For
some children the illness becomes a formidable problem causing numerous visits
to the hospital emergency room and multiple hospitalizations
Household pets are the most common source of allergic reactions to animals.
Many people think that pet allergy is provoked by the fur of cats and dogs. But
researchers have found that the major allergens are proteins secreted by oil
glands in the animals' skin and shed in dander as well as proteins in the
saliva, which sticks to the fur when the animal licks itself. People have always
said that when it comes to allergies, cats are worse than dogs. We now know that
it is because cats lick themselves more than dogs, thereby spreading the
allergens. In addition, cats may be held more and spend more time in the house,
close to humans. Urine is also a source of allergy-causing proteins. When the
substance carrying the proteins dries, the proteins can then float into the air.
Some rodents, such as guinea pigs and gerbils, have become increasingly popular
as household pets. They, too, can cause allergic reactions in some people, as
can mice and rats. Urine is the major source of allergens from these animals.
Allergies to animals can take two years or more to develop and may not subside
until six months or more after ending contact with the animal. Carpet and
furniture are a reservoir for pet allergens, and the allergens can remain in
them for four to six weeks. In addition, these allergens can stay in household
air for months after the animal has been removed. Therefore, it is wise for
people with an animal allergy to check with the landlord or previous owner to
find out if furry pets had lived previously on the premises.
An allergy to dust found in houses is perhaps the most common cause of
perennial allergic rhinitis. House dust allergy usually produces symptoms
similar to pollen allergy.
What is house dust?
Rather than a single substance, house dust is a varied mixture of potentially
allergenic materials. The particles seen floating in a shaft of sunlight may
contain fibers from different types of fabrics; cotton lint, feathers, and other
stuffing materials; bacteria; mold and fungus spores (especially in damp areas);
food particles; bits of plants and insects; and other allergens peculiar to an
individual home. Dust also may contain microscopic mites. These mites also live
in bedding, upholstered furniture, and carpets. Ordinarily, they would thrive in
summer and die in winter. However, in a warm, humid house, they continue to
thrive even in the coldest months. These waste products, which are proteins,
actually provoke the allergic reaction. House dust mite allergy is the major
year-round allergy in the world, though ragweed is more prevalent in the United
States. Waste products of cockroaches are also an important cause of allergy
symptoms from household allergens, particularly in some urban areas of the
What are Dust Mites?
Dust mites are tiny animals you cannot see. Every home has dust mites. They
feed on skin flakes and are found in mattresses, pillows, carpets, upholstered
furniture, bedcovers, clothes, stuffed toys, and fabric or other fabric-covered
items. Body parts and feces of dust mites can trigger allergic reactions in
sensitive individuals. The presence of dust mites in a home are in no way an
indication of the sanitary conditions in the home.
Along with pollens from trees, grasses, and weeds, molds are an important
cause of seasonal allergic rhinitis. People allergic to molds may have symptoms
from spring to late fall. The mold season often peaks from July to late summer.
Unlike pollens, molds may persist after the first killing frost. Some can grow
at subfreezing temperatures, but most become dormant. Snow cover lowers the
outdoor mold count dramatically but does not kill molds. After the spring thaw,
molds thrive on the vegetation that has been killed by the winter cold. In the
warmest areas of the United States, however, molds thrive all year and can cause
year-round (perennial) allergic problems. In addition, molds growing indoors can
cause perennial allergic rhinitis even in the coldest climates.
What is mold?
There are thousands of types of molds and yeast, the two groups of plants in
the fungus family. Yeasts are single cells that divide to form clusters. Molds
consist of many cells that grow as branching threads called hyphae. Although
both groups can probably cause allergic reactions, only a small number of molds
are widely recognized offenders. The seeds or reproductive particles of fungi
are called spores. They differ in size, shape, and color among species. Each
spore that germinates can give rise to new mold growth, which in turn can
produce millions of spores.
What is mold allergy?
When inhaled, microscopic fungal spores or, sometimes, fragments of fungi may
cause allergic rhinitis. Because they are so small, mold spores may evade the
protective mechanisms of the nose and upper respiratory tract to reach the
lungs. In a small number of people, symptoms of mold allergy may be brought on
or worsened by eating certain foods, such as cheeses, processed with fungi.
Occasionally, mushrooms, dried fruits, and foods containing yeast, soy sauce, or
vinegar will produce allergic symptoms. There is no known relationship, however,
between a respiratory allergy to the mold Penicillium and an allergy to
the drug penicillin, made from the mold.
Where do molds grow?
Molds can be found wherever there is moisture, oxygen, and a source of the
few other chemicals they need. In the fall they grow on rotting logs and fallen
leaves, especially in moist, shady areas. In gardens, they can be found in
compost piles and on certain grasses and weeds. Some molds attach to grains such
as wheat, oats, barley, and corn, making farms; grain bins, and silos likely
places to find mold.
Hot spots of mold growth in the home include damp basements and closets,
bathrooms (especially shower stalls), places where fresh food is stored,
refrigerator drip trays, house plants, air conditioners, humidifiers, garbage
pails, mattresses, upholstered furniture, and old foam rubber pillows. Bakeries,
breweries, barns, dairies, and greenhouses are favorite places for molds to
grow. Loggers, mill workers, carpenters, furniture repairers, and upholsterers
often work in moldy environments.
Which molds are allergenic?
Like pollens, mold spores are airborne allergens that are abundant, easily
carried by air currents, and allergenic in their chemical makeup. Found almost
everywhere, mold spores in some areas are so numerous they often outnumber the
pollens in the air. Fortunately, however, only a few dozen different types are
significant allergens. In general, Alternaria and Cladosporium (Hormodendrum)
are the molds most commonly found both indoors and outdoors throughout the
United States. Aspergillus, Penicillium, Helminthosporium, Epicoccum,
Fusarium, Mucor, Rhizopus, and Aureobasidium (Pullularia) are also
Are there other mold-related disorders?
Fungi or microorganisms related to them may cause other health problems
similar to allergic diseases. Some kinds of Aspergillus may cause several
different illnesses, including both infections and allergy. These fungi may
lodge in the airways or a distant part of the lung and grow until they form a
compact sphere known as a "fungus ball." In people with lung damage or serious
underlying illnesses, Aspergillus may grasp the opportunity to invade the
lungs or the whole body. In some individuals, exposure to these fungi also can
lead to asthma or to a lung disease resembling severe inflammatory asthma called
allergic bronchopulmonary aspergillosis. This latter condition, which occurs
only in a minority of people with asthma, is characterized by wheezing,
low-grade fever, and coughing up of brown-flecked masses or mucus plugs. Skin
testing, blood tests, X-rays, and examination of the sputum for fungi can help
establish the diagnosis. Corticosteroid drugs are usually effective in treating
this reaction; immunotherapy (allergy shots) is not helpful.
Indoor Air Regulations and Mold
Standards or Threshold Limit Values (TLVs) for airborne concentrations of
mold, or mold spores, have not been set. Currently, there are no EPA regulations
or standards for airborne mold contaminants.
Synthetic chemicals are all around us. They're in the products we use, in the
clothes we wear, in the food we eat, in the air we breathe at work. Because
chemicals are everywhere in the environment, it's not possible to escape
exposure. No wonder, then, that many people have become sensitized to the
chemicals around them. For some people the sensitization is not too serious a
problem. They may have what appears to be a minor allergy to one or more
chemicals. Chemical sensitivity is not a true allergic reaction because IgE is
not actually present. Other people are much more seriously affected. They may
feel tired all the time, and suffer from mental confusion, breathing problems,
sore muscles, and a weakened immune system. Such people suffer from a condition
referred to as Multiple Chemical Sensitivity (MCS).
What is Multiple Chemical Sensitivity?
MCS is a disorder triggered by exposures to chemicals in the environment.
Individuals with MCS can have symptoms from chemical exposures at concentrations
far below the levels tolerated by most people. Symptoms occur in more than one
organ system in the body, such as the nervous system and the lungs. Exposure may
be from the air, from food or water, or through skin contact. The symptoms may
look like an allergy because they tend to come and go with exposures, though
some people's reactions may be delayed. As MCS gets worse, reactions become more
severe and increasingly chronic, often affecting more bodily functions. No
single widely available medical test can explain symptoms. In the early stages
of MCS, repeat exposure to the substance or substances that caused the initial
health effects provokes a reaction. After a time, it takes less and less
exposure to this or related chemicals to cause symptoms. As the body breaks
down, an ever-increasing number of chemicals, including some unrelated to the
initial exposure, are found to trigger a reaction. MCS affects the overall
health and feeling of well being of those with the disorder. It typically
impairs many bodily functions including the nervous system and digestion. Each
individual affected by MCS has a unique set of health problems. A chemically
sensitive person may also have other preexisting health conditions. Many
affected people experience a number of symptoms, in relation to their chemical
exposures. MCS may result from a single massive exposure to one or more toxic
substance or repeated exposures to low doses. People with MCS may become
partially or totally disabled for several years or for life.
MCS is difficult for physicians to define and diagnose. There is no single
set of symptoms which fit together as neither a syndrome, nor a single
diagnostic test for MCS. Instead, physicians should take a complete patient
history that includes environmental and occupational exposures, and act as
detectives in diagnosing this problematic condition. After the onset of MCS, a
person's health generally continues to deteriorate. It may only begin to improve
once the chemical sensitivity condition is uncovered. While a number of
treatments may help improve the baseline health status for some patients, at the
present time, there is no single "cure" except avoidance.
Each spring, summer, and fall, tiny particles are released from trees, weeds,
and grasses. These particles, known as pollen, hitch rides on currents of air.
Although their mission is to fertilize parts of other plants, many never reach
their targets. Instead, they enter human noses and throats, triggering a type of
seasonal allergic rhinitis called pollen allergy, which many people know as hay
fever or rose fever (depending on the season in which the symptoms occur). Of
all the things that can cause an allergy, pollen is one of the most widespread.
People with pollen allergies often develop sensitivities to other troublemakers
that are present all year, such as dust mites. Year-round airborne allergens
cause perennial allergic rhinitis, as distinguished from seasonal allergic
What is pollen?
Plants produce microscopic round or oval pollen grains to reproduce. In some
species, the plant uses the pollen from its own flowers to fertilize itself.
Other types must be cross-pollinated; that is, pollen must be transferred from
the flower of one plant to that of another plant of the same species. Insects do
this job for certain flowering plants, while other plants rely on wind
transport. The types of pollen that most commonly cause allergic reactions are
produced by the plain-looking plants (trees, grasses, and weeds) that do not
have showy flowers. These plants manufacture small, light, dry pollen granules
that are custom-made for wind transport.
Where is pollen most common?
Most allergenic pollen comes from plants that produce it in huge quantities.
A single ragweed plant can generate a million grains of pollen a day. Samples of
ragweed pollen have been collected 400 miles out at sea and 2 miles high in the
air. The chemical makeup of pollen is the factor that determines whether it is
likely to cause hay fever. For example, pine tree pollen is produced in large
amounts by a common tree, which would make it a good candidate for causing
allergy. The chemical composition of pine pollen, however, appears to make it
less allergenic than other basic types. Because pine pollen is heavy, it tends
to fall straight down and does not scatter. Therefore, it rarely reaches human
noses. Among North American plants, weeds are the most prolific producers of
allergenic pollen. Ragweed is the major culprit, but others of importance are
sagebrush, redroot pigweed, lamb's quarters, Russian thistle (tumbleweed), and
English plantain. Grasses and trees, too, are important sources of allergenic
pollens. Although more than 1,000 species of grass grow in North America, only a
few produce highly allergenic pollen. These include timothy grass, Kentucky
bluegrass, Johnson grass, Bermuda grass, redtop grass, orchard grass, and sweet
vernal grass. Trees that produce allergenic pollen include oak, ash, elm,
hickory, pecan, box elder, and mountain cedar. It is common to hear people say
that they are allergic to colorful or scented flowers. In fact, only florists,
gardeners, and others who have prolonged, close contact with flowers are likely
to become sensitized to pollen from these plants. Most people have little
contact with the large, heavy, waxy pollen grains of many flowering plants
because this type of pollen is not carried by wind but by insects such as
butterflies and bees.
When do plants make pollen?
One of the most obvious features of pollen allergy is its seasonal
nature--people experience it symptoms only when the pollen grains to which they
are allergic are in the air. Each plant has a pollinating period that is more or
less the same from year to year. Exactly when a plant starts to pollinate seems
to depend on the relative length of night and day--and therefore on geographical
location--rather than on the weather. (On the other hand, weather conditions
during pollination can affect the amount of pollen produced and distributed in a
specific year.) Thus, the farther North you go, the later the pollinating period
and the later the allergy season. A pollen count, which is familiar to many
people from local weather reports, is a measure of how much pollen is in the
air. This count represents the concentration of all the pollen (or of one
particular type, like ragweed) in the air in a certain area at a specific time.
It is expressed in grains of pollen per square meter of air collected over 24
hours. Pollen counts tend to be highest early in the morning on warm, dry,
breezy days and lowest during chilly, wet periods. Although a pollen count is an
approximate and fluctuating measure, it is useful as a general guide for when it
is advisable to stay indoors and avoid contact with the pollen.
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Revised: April 12, 2012 .
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