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A Short Allergy Primer

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A Short Allergy Primer

The number of those suffering from allergy has multiplied over the last three decades. More and more people react to allergenic substances (antigens).In Germany, just over 9 % of the population is said to suffer from hay fever (i.e. four times as many males and females as 30 years ago, while the number of individuals suffering from allergic asthma has doubled over the same period. Not infrequently, an additional allergy joins forces with the one already existing. This may result in a significant reduction of the wellbeing of those affected (as well as their families).

The reasons why the incidence of allergic reactions should rise in this way are multilayered. Not all the interrelated factors have as yet been wholly explained. Here are some of the possible causes:

  • A growing number of substances produced by biotechnical or chemical synthesis (in Europe alone, roughly 130,000 chemical substances are used in products, hundreds more are added each year.)
  • A rising number of stressful situations day by day – permanent stress – a lessening of psychological well-being. The psyche can also be one of the factors increasing (or lowering, respectively) the likelihood that the body will develop an allergic reaction when coming into contact with antigens.
  • An increasing amount of imported, exotic fruit; proliferation of moulds during long storage periods
  • Smoking (tobacco smoke = most significant air contaminant in buildings)
  • Harmful substances in the home. Too much time spent indoors. It is a proven fact that the increasing pollution of interiors reaches particularly high levels: humid cellars, damp spots under the wallpaper and behind wardrobes, damp laundry, poorly ventilated or unventilated bathrooms, etc.
  • Air pollution
  • Harmful substances in the workplace

What does the term “allergy” actually mean?

An allergy is an excessive (= the body’s defence against foreign substances is too strong) and undesired reaction (= hypersensitive reaction and/or sensitisation) the body produces when exposed to specific substances contained in its environment: the allergens (antigens). Many of these allergens, such as pollen, insect poison, animal hair, mites and foodstuffs, derive from nature. Others are contained in known pollutants such as car exhaust fumes. This overreaction is undesirable as it may lead to illness if it continues for a longer period of time: inflammatory processes may affect tissues and organs. When doctors speak of sensitisation, they mean this increase in sensitivity – to different types of birch pollen, for example. A sensitivity to certain substances does not necessarily result in an allergy in every individual who has it, but once an allergic reaction has set in for the first time, it will reoccur on each occasion when even a small amount of the allergen is present.

Allergy triggers – a few of very many

  • Pollen – the pollen of grasses, trees, or bushes
  • Dust particles containing animal hair or scales
  • House dust. Dust mites are arachnid organisms only half a millimetre in size. They preferably feed on human skin cells and their favourite abiding places are our beds. So-called “house dust” is a mixture of the dried excreta of these dust mites and other dust particles.
  • Mould and fungi
  • Flour, cement
  • Food additives
  • Air pollutants, in particular formaldehyde, isocyanates (in foams) and sulphur dioxide
  • Chemicals in cleaning agents, cosmetics, etc.
  • Chemicals in the workplace
  • Medicines, most of all penicillin, contrast agents injected into the veins for x-ray examinations, painkillers containing metamizol, substances used for local anaesthesia, skin ointments containing Peruvian balsam, various ingredients of suntan lotions.

Possible consequences of allergies

organs symptoms and disorders
eye conjunctivitis
swelling of eyelids
respiratory tract sinuses
sneezing attacks
swelling of larynx and throat
shortness of breath, bronchial asthma
inflammation of pulmonary alveoli
skin welts on the skin
swellings
eczema
neurodermatosis
gastrointestinal tract nausea, diarrhoea
inflammation of the stomach lining
vascular system vascular inflammation
circulatory collapse (shock)
blood reduction and destruction of blood cells or platelets
central nervous system fever
joints inflamed joints
kidneys inflammation of the kidneys

(Source: "Allergien – Das Immunsystem auf Abwegen", publisher: Stiftung Warentest)

What causes allergies?

The body’s “defences” – our immune system

If we wish to understand the ailment “allergy”, we first need to know how the immune system of the body functions and what happens when it reacts “excessively”.

In order to trigger an allergic reaction, foreign substances must penetrate the body’s external borders – i.e. either the skin or the mucous membranes. Our skin and our mucous membranes are the human body’s “first line of defence”. But this initial barrier is a permeable shield. And it needs to be, because metabolic waste, for example, is excreted through the skin by sweating and an intensive exchange of interior and exterior matter also takes place while the pulmonary alveoli breathe. It is hence also possible that harmful substances penetrate the skin, particularly in areas where it has already been damaged.

Any germs that successfully penetrate the protective barrier “skin” hit a second line of defence: the immune system. This “intelligent” defence system is able to recognise the germs as intruders on account of their characteristic structures.

But the immune system’s response can also be inappropriate and damage the organism, for example when it mistakes the body’s own cells for intruders: in this case, the body fights itself in a self-destructive manner (autoimmune disorders). The potential of hypersensitive reactions (allergies) or autoimmune disorders (such as colitis ulcerosa, which affects the large intestine) occurring is the price the body has to pay for its ability to protect itself.

Allergies are the most common form of undesirable reaction of the body’s immune system. Once again, the body is fighting alien intruders. Only that in this case it overestimates the threat posed by the invading substances.

The structure of our immune system

Lymphocytes (lymph + cyto = cell) play a key role in our immune system. They are the smallest of the white blood cells. They are produced in the bone marrow (B-lymphocytes; B = bone marrow) and in the thymus (T-lymphocytes) and over time mature into specialized fighting cells. From here they move along with the body fluids to areas where immune reactions primarily occur, such as the spleen and lymph nodes or the lymphatic tissue, which embraces the surface of our mucus membranes.

There are two types of immune response: our congenital immunity (which is at our disposal from birth in the form of specific substances and phagoytes contained in the body fluids) and the acquired (“intelligent” = adaptive) immunity.

Acquired immunity

At the time when the lymphocytes leave their production locations, they are not yet very specialised. They will only become so by their contact with extrinsic substances: it is due to their influence that the B-lymphocytes produced in the bone marrow initially develop into so-called plasma cells. With the help of the T-lymphocytes produced in the thymus, they are then able to produce protein molecules capable of defensive action: our immunoglobulins (globulin = small sphere). These finally function as antibodies and fight foreign substances with their special tentacles (antigens or allergens). This reaction to antigens or allergens creates the prerequisites for the activation of various immune cells which either destroy foreign invaders independently or with the help of aggressive substances.

Immunoglobulins

All our antibodies are immunoglobulins (Ig). These are divided into five classes according to function. Their respective significance for our allergic reactions is highly varied.

Immunoglobulin G (IgG)
It already protects the foetus, for it can cross the “placental barrier”, i.e. the unborn child’s defence screen against viruses and bacteria.
IgG is involved in two types of allergic reaction:
  • Asthma, triggered by fungus spores (aspergillomycosis)
  • Inflammation of the pulmonary alveoli (alveolitis
Immunglobulin A (IgA)
This is created directly in the body’s surface areas where the exposure to allergens occurs – most of all in the lungs and intestines. Along with other secretions, IgA covers the surface of the mucus membranes and prevents that germs and allergens establish themselves here or even penetrate any deeper. If this defence line is successful, no further parts of the body’s immune system will be mobilised, which means that potential allergic reactions will not occur. But if the skin or mucus membrane should be weakened or damaged, an allergic reaction would be more likely.
Immunoglobulin M (IgM)
IgM is mainly found in the blood vessels and, together with IgG, helps to clump particles and molecules so that the phagocytes can absorb them more easily. IgM is simultaneously involved in slowing down the escalation of allergic reactions.
Immunglobulin D (IgD)
IgD is produced by the “young” B-lymphocytes and is attached to their surface. Its exact role in allergic reactions is as yet largely unknown. The IgD circulates with the lymphocytes in our blood serum, perhaps providing them with a snare to trap antigens.
Immunglobulin E (IgE)
IgEis created in the lymphatic tissue directly adjoining the air passages and the gastro-intestinal canal and enters the blood stream from there. Although only produced by the body in minute amounts, this antibody triggers approximately 90 percent of all allergic reactions.
A specific feature of IgE is responsible for the unpleasant consequences of most allergies: the protein cell easily bonds with the body cells in the skin and mucus membrane which may cause allergic symptoms. If the antibody in this position comprises any allergens it has trapped in its snares (antigen-antibody reaction), it will affect the function of various cells and as such set off an inflammatory reaction.

In trying to determine how and where the immunoglobulins (=antibodies) operate and how they affect the 4 different types of allergies, one needs to consider the following facts:

Our immune system has two kinds of “immune response”:

  1. Humoral response (humor -- Latin: = fluid)
    Most immune system reactions are mediated by antibodies which can be produced in large quantities by the B-lymphocytes as soon as allergens invade. Because these antibodies are distributed throughout the body in the body fluids, this reaction is called the humoral response.
  2. Cellular or cell-mediated response
    The cellular or cell-mediated response consists of a direct attack carried out by the immune cells. If, for example, any allergens attach to a body cell, the T-lymphocytes as T-killer cells can latch onto them and destroy them. This is referred to as the cellular or cell-mediated response, because entire cells – and not just their products (= antibodies) - attack the invader.

A further “key”: mast cells

Mast cells have an important role to play when an allergic reaction occurs. They are white blood cells which are produced in the bone marrow and distributed in the loose connective tissue of all our organs (except the brain) and were given this name because they are “filled to the brim” with small, substance-filled bubbles.

Two features of theirs, in particular, make them very important for the control of most allergies:

  • IgE antibodies can attach quite easily to their surface as soon as allergens invade. At first contact, the mast cells are only equipped with a few specific antibodies (sensitisation).
  • The allergens trapped during an antigen-antibody reaction affect the permeability of the mast cell membrane (membrane = cell border) The substance-filled bubbles can escape from the mast cell interior. These bubbles then in turn release their contents: the mediators, for example histamine. The mediators trigger inflammation reactions in the surrounding tissue.
    In addition to the “firmly rooted” mast cells, there are also “circulating mast cells” (referred to as “basophile leucocytes” in medicine) which are carried through the body by the blood and enter the tissue.

Mediators

Mediators, which are also called inflammation cells, are the substances directly involved in most allergy symptoms. And they are not only involved in allergic disorders, but also in all other inflammatory processes.

Different mediators have various effects. Histamine is probably the best-known and most thoroughly researched mediator.

  • It is their release from the mast cells in our mucus membranes that causes our nose, mouth and eyes to itch and our mucus production to increase. In the bronchia, all smooth muscles contract, causing cramps and shortness of breath. On the skin, the same mediator causes itchy hives and redness.
  • Under the influence of histamine, the stomach steps up the production of gastric acids and the intestine reacts with cramping and diarrhoea. In high concentrations, histamine can result in a shock reaction (see anaphylactic shock below).

The allergy types

There are 4 known types of allergic reaction. They differ in the period of time elapsing between allergen exposure and the allergic reaction itself as well as in the mechanics of the immune response:

Typ I: Anaphylactic reaction or immediate type allergy.
Over 90 percent of all allergies fall into this class. The symptoms appear immediately following contact with the allergen. They are based on the increased production of the antibody IgE, which – together with the mast cells in the tissue – absorb allergens. After an initial sensitisation phase, each subsequent contact with an allergen will cause the mast cells to release mediators which trigger inflammation and allergic symptoms.
Typical illnesses associated with Type I:
  • allergic rhinitis (common cold symptoms)
  • allergic asthma
  • hives
  • angioedema (swelling of vessels)
  • food allergy
  • anaphylactic shock (see above)
Typ II: Zytotoxic reaction (Greek: zyto = cell)
This type of allergy destroys cells, because the attack concerns the surfaces of those cells of the organism that have bonded with small, extraneous bodies. This turns the cells themselves into allergens.
Class IgG and IgM antibodies not only bond with invading substances, but also with the defence cells engaged in fighting the allergen. Because the phagocytes have difficulties absorbing complete body cells, they excrete cell-destroying enzymes. These enzymes not only destroy the cells which have turned into allergens, but also damage the surrounding tissue. The consequence is an allergic disorder. If the body cells thus attacked have themselves produced the foreign substance on their membranes, we speak of an autoimmune disorder.
In all other cases, the extraneous substance was introduced from the outside and has bonded with the cells. (Allergic reactions to drugs or their breakdown products)
Typical disorders associated with Type II:
  • Reduction of the white blood cell count (agranulocythaemia)
  • Destruction of red blood cells (haemolytic anaemia)
  • Blood type incompatibility during pregnancy
Typ III: immune complex reaction
Under certain conditions, allergens and antibodies form multi-sectional complexes which sometime even comprise bound body cells. Primarily responsible for this type of reaction is the antibody IgG. It attracts various defence cells and defence factors which on the one hand break down immune complexes with enzymes, but on the other damage the surrounding tissues (Type II). If the body’s immune defence is incapable of keeping the number of immune complexes in check, these may accumulate in the organs and cause inflammation, for instance in the joints or kidneys.
The allergic symptoms do not appear immediately, but after a few hours or even days. This is the case with, for example, serum sickness caused by medication or when the pulmonary alveoli become inflamed due to repeated exposure to allergens contained in hay, straw or dry leaves.
Typical disorders associated with Type III:
  • Inflammation of the vessels
  • Serum Sickness via injection of foreign protein
  • Inflammation of pulmonary alveoli
  • Inflammation of the kidneys
  • Inflammation of the joints
Typ IV: Cellular immune reaction
When certain defence cells in the immune system, the T-lymphocytes, react with allergens (i.e. not with their products, the immunoglobulins or antibodies), this is called a cell mediated or cellular response. As with a Type II reaction, the allergens are created when small, extraneous particles (half-allergens, half-antigens) invade the organism and bond with the protein molecules in body cells. With the help of special cells, the T-lymphocytes are then able to recognise these minute invaders and destroy them on contact.
In fighting these foreign particles, the T-lymphocytes release substances that not only encourage inflammation, but also attract and activate phagocytes, for example. These mediating substances are called “lymphokines” (lymph + kinese – Greek: = movement) The name is based on their mobility.
As with Type I allergies, there is a sensitisation period that can be relatively long and finally produces a strong reaction on each subsequent occasion the organism comes in contact with the allergen again.
Typical disorders associated with Type IV:
  • Contact eczema (contact dermatitis, contact allergy)
  • Rashes caused by medication (medication exanthema)

Sources:
"Allergien -- Das Immunsystem auf Abwegen ", Herausgeber Stiftung Warentest
"Kursbuch Gesundheit", Verlag Kiepenheuer & Witsch, Köln
"Mensch -- Körper -- Krankheit", jungjohann Verlag, Neckarsulm

References

We recommend the guidebook “Allergien – Das Immunsystem auf Abwegen" for anyone eager to find comprehensive information about allergies. The book is published by the Stiftung Warentest (a German consumer agency) and will be easily understood by a layperson. On its first pages you will find information about self-help groups and ambulatories, along with references for further study and reading. (Order Number: ISBN 3-931908-24-0)