allergy

Synonyms for allergy

Hypersensitivity, hypersensitivity

Definition of allergy

allergy (allo = changed, ergos = Activity) denotes an excessive reaction of the Immune system on so-called environmental antigens, which are normally not pathogenic and are tolerated by the body. This Antigens will too Allergens called and describe certain tiny substances or their parts that activate the immune system.

Under Cross allergy one understands the simultaneous existence of several Allergies due to structural similarities of the antigens. For example, a person who is allergic to pollen often also reacts sensitively to pome fruit.

Epidemiology

The allergy usually occurs in childhood, but can also manifest itself anew at any age. Food allergies occur more frequently in the first few months and between the ages of 15 and 35.

The most common allergy is directed against pollen with 60%, followed by allergies to mites and animals with 15% and allergies to drugs and food with less than 5%.

In western countries there has been an increase in the frequency of allergies for about 30 years. In Germany, for example, allergic hay fever currently affects 15% of the population, 5% suffer from bronchial asthma and 1.5% from a food allergy. Up to 20% of all German school children suffer from neurodermatitis (Atopic dermatitis).

Causes of the allergy

Genes are one of the causes of allergies. If at least one parent suffers from an allergy, the risk for the children of developing such an allergy also increases.

Atopy should also be mentioned in this context. Atopy describes the inherited willingness of the body to form antibodies (IgE) to normal antigens in the environment. The result is allergic diseases, including bronchial asthma, neurodermatitis (atopic dermatitis), hay fever (allergic Rhinitis and Conjunctivitis), Wheals of the skin (Hives, Urticaria) as well as food and drug allergies.

The so-called cause is also being discussed Hygiene hypothesis. This states that there has been an increase in allergies in recent years because people grow up too sterile and come into contact with too few germs in childhood. As a result, the immune system cannot develop adequately and is therefore allergic to normal environmental antigens.

The most common triggering allergens include pollen, house dust mites, pet dander, food (e.g. eggs, milk, nuts, soy, wheat) and medication (e.g. Antibiotics).

Pathogenesis of Allergy

An allergy can only occur if first contact with the triggering substance (antigen) and a subsequent sensitization has taken place. After the initial contact, the immune system reacts that shows no external symptoms, i.e. the patient does not yet notice an allergy. This is then followed by the sensitization phase, which lasts 1 to 3 weeks and which also takes place in the immune system. Special proteins are produced (antibody), which are directed against the antigen and sensitized cells (Lymphocytes). The patient usually does not notice this reaction either, but this turns the antigen into an allergen. This means that if the patient comes into contact with this antigen again, a visible reaction with symptoms of the allergy and complaints is triggered.

This visible reaction of the allegy can be of a type Right and Coombs will be assigned. There are 4 types in total:

  • Type 1 allergy = IgE-mediated immediate reaction (IgE = antibodies, immunoglobulin E)
  • Type 2 allergy = antibody-mediated cytotoxic reaction (IgG, IgM)
  • Type 3 allergy = immune complex-mediated reaction (IgG)
  • Type 4 allergy = cell-mediated reaction

These types show differences in the reaction time after contact with the allergen, the affected organs and the mechanism of action.

Types 1 to 3 of allergies are mediated by antibodies; they are called humoral reactions. Type 4, on the other hand, is mediated by cells, which is why it is defined as cell-mediated.

Reaction type 1 of an allergy is most common and is found, for example, in hay fever or bronchial asthma. The triggering allergens include pollen, mites in bed, animal hair, food or medication. After contact with them, the allergic reaction occurs within 30 minutes on the skin, mucous membranes, airways or in the digestive tract. As a result of the release of certain substances (Histamine, serotonin, leukotrienes, prostaglandins) from special cells of the immune system, the mast cells, the typical complaints such as runny nose, itching etc. occur, this reaction is referred to as mast cell degranulation. It happens when the allergens bind to certain antibodies, namely IgE. These IgE are located on the surface of the mast cells. Ig stands for immunoglobulins, E denotes the class.

The sequence described characterizes the so-called early phase or acute phase reaction of this type of reaction; after 3 to 8 hours there is also a late phase with inflammation and damage to the tissue, which can last for several days.

Reaction type 2 of the allergy occurs, for example, in a certain form of anemia (hemolytic anemia). The reaction only occurs after 5 to 8 hours. Allergens are usually drugs and the organs affected are the blood cells or the kidneys. The mechanism of action is characterized by the destruction of cells (lysis). Antibodies formed against certain structures on the cell surface are responsible for this lysis. The antibodies include IgG and IgM, i.e. immunoglobulins of class G and M.

Reaction type 3 of the allergy takes place on the skin or systemically after 2 to 8 hours after contact with the allergen (mold, bacteria, medication, etc.). In this process, many complexes of allergens and antibodies directed against them develop in the blood in a short time. These are deposited in the tissue as a result of the rapidly developing amount. This happens, for example, with inflammation of the kidney corpuscles (glomerulonephritis) or with serum sickness.

Reaction type 4 of the allergy takes the longest time, 24 to 72 hours to react. This can be seen, for example, on the skin, liver, kidneys or lungs. The triggering allergens include nickel and other metals, drugs, disinfectants and cosmetics. A typical disease is contact dermatitis, which is an inflammatory change in the skin (eczema). The reaction is set in motion by specially sensitized immune cells (T cells) by activating other immune cells (macrophages = phagocytes, natural killer cells), which in turn damage other cells.

Read more on this topic at: Contact dermatitis

therapy

The allergy can initially be treated by avoiding allergens, i.e. by avoiding and reducing the triggering substances or allergens or by stopping the drugs that cause them.

Since this is not always possible or only with difficulty depending on the allergen, the therapy for certain diseases can be supported with the help of medication. The mast cells can be stabilized (Cromoglicic acid), the effect of some of their released mediators are suppressed (antihistamines, leukotriene antagonists) or the inflammatory reaction is suppressed (steroids).

There is also the option of hyposensitization in the event of allergies to pollen, bee venom, house dust mites or mold. The corresponding allergen is usually injected under the skin in increasing concentrations over a period of 3 years in order to ensure that the immune system tolerates the allergen and no longer shows the allergic reaction.

This treatment is successful in about 75% of patients. The exact mode of action is not clear.

Anaphylactic shock as an acute emergency is treated with fluids and oxygen, cortisone, medication to dilate the airway (? -Imetics) and catecholamines (adrenaline, dopamine). Resuscitation is used as the last measure in the event of respiratory or cardiac arrest.

Read more on this topic at:

  • Therapy for an allergy
  • These drugs help if you have an allergy

Allergy prophylaxis

Are useful for the prophylaxis of an allergy Breastfeeding of children and growing up in a rural setting.

However, if an allergy already exists, the allergic reaction can be triggered by avoiding the allergen (Allergen avoidance) can be prevented.

Summary

A allergy is the hypersensitivity reaction of the immune system to allergens that occur in the environment. They are particularly visible on the skin, eyes, airways and intestines as itching, reddening, wheals, shortness of breath or diarrhea, for example.

Allergies are treated primarily by avoiding the triggering allergens. There are also drugs or desensitization.