Allergies: what is it?
The human body has its own defense against pathogens – the immune system . However, this complex and extremely efficient system is sometimes prone to breakdowns. A functional disorder can manifest itself, for example, in the form of an allergy . In such a case, the immune system works more zealously than desired: it responds to harmless stimuli with defense mechanisms. Allergy-causing substances are referred to as allergens . All allergies belong to a large group of body reactions to foreign substances, which are referred to as immune reactions . Among allergies, early-type reactions and late-type reactions are most common.
Four types of allergic reactions
Experts distinguish a total of four types of allergic reactions, which are briefly described in the following table and further in the text.
| Designation (type) | The course of the reaction | The time from contact with the allergen to the onset of an allergic reaction | How the reaction can manifest itself (examples) |
| type I immunopathological reaction ( early type allergic reaction ) | is mediated by antibodies of the IgE class ; signaling molecules (primarily histamine ) are released | several seconds to minutes (or a second reaction occurs after 4-6 hours) |
|
| immunopathological reaction II. type ( allergic reaction of the cytotoxic type ) | antigen -antibody complexes are formed ; the immune system destroys the body’s own cells | 6-12 hours |
|
| immunopathological reaction III. type ( allergic reaction of immune complex type ) | antigen-antibody complexes are formed; substances are released that damage tissues | 6-12 hours |
|
| immunopathological reaction IV. type ( allergic reaction of late type ) | is mediated by cells ( T-lymphocytes ) | 12-72 hours |
|
Allergic reaction of the early type
Allergic reaction of the early type, or immunopathological reaction of type I, is the most frequently occurring type of allergy. An exaggerated reaction of the immune system occurs practically immediately after contact with the allergen – within seconds to minutes. The first contact with an allergy-causing substance occurs without symptoms. In an early-type allergic reaction, so-called IgE antibodies are created and a chain reaction starts. Among other things, type I immunopathological reaction can be caused by certain pollens, medicines , pet fur, food or insect poisons. During this type of allergic reaction, histamine is released into the bloodstream – a substance that causes typical allergy symptoms, such as itching, reddening of the skin or skin rash, sneezing, tissue swelling , or indigestion . In the worst case, anaphylactic shock can occur , when there is such a significant drop in blood pressure that it threatens the life of the affected person.
Hereditary tendency to the disease of early-type allergies mediated by IgE antibodies is referred to as atopy . Atopic patients also have an increased risk of developing asthma or atopic eczema . When allergic asthma occurs, inflammation of the bronchi also occurs .
Allergic reaction of late type
An allergic reaction may not appear immediately. In the case of a late-type allergic reaction or immunopathological reaction IV. type, the symptoms only appear after a certain period of time has passed since re-contact with the allergen, as is the case, for example, with the often occurring allergy to nickel. Even in this case, the first contact with the allergen takes place without symptoms. In a late-type allergic reaction, so-called T-lymphocytes are at the beginning of the inflammatory reaction.
Other types of allergic reactions
Immunopathological reactions II. and III. type do not occur as often as the reactions described above, but are still worth mentioning at least briefly.
- Allergic reaction of cytotoxic type or immunopathological reaction II. type occurs very rarely. In this case, an antibody binds to the antigen (bound to the surface of the cell or occurring on the surface of the organ ), thanks to which the immune system then destroys the target cell (marked by the antigen-antibody complex). An example is the situation when some drugs bind to the surface of blood cells . Antibodies bind to these drugs (antigens) and the immune system destroys the body’s own blood cells. During a blood test, this can be manifested, for example, by a decrease in the number of white blood cells (especially granulocytes ) or blood platelets ( thrombocytes ).
- Allergic reaction of the immunocomplex type or immunopathological reaction III. type is characterized by massive production of antibodies. Upon contact with an allergen, large clusters of immune complexes are quickly formed, which are antibodies ( immunoglobulins ) bound to antigens. Immunocomplexes can then precipitate (precipitate) in some organs, and these precipitates subsequently cause inflammation. If a person inhales an allergen, these precipitates are formed in the alveoli and cause so-called exogenous allergic alveolitis (one of its types is farmer’s lung, which occurs in some agricultural workers). Other organs can also be affected, for example the vascular system (vasculitis) or the kidneys ( glomerulonephritis ).
Why do allergies occur?
Allergies usually do not develop overnight. From the first symptoms to the moment when the diagnosis is made , several years often pass. Allergies can happen to any of us. Even if, for example, someone has had a cat for many years without having an allergic reaction to it, he may still develop an allergy to animal fur over time .
Genetic predisposition seems to play an important role in allergies . The probability of developing allergies is clearly higher in children whose parents are allergic. The development of our civilization probably also contributes substantially to the increasing incidence of allergies in Western countries. As a result of the increasingly “sterile” environment in industrialized countries, the immune system of children is less and less exposed to the necessary stimuli and thus less “trained”. If the first signs of a tendency to allergies (atopy) occur in early childhood, such as atopic dermatitis or so-called “milk crust” ( seborrheic dermatitis affecting infants), the child has an increased risk of developing allergies in the future. In this sense, passive smoking is also particularly risky .
Diagnosis and treatment of allergies
Blood tests and skin tests are mainly used to diagnose allergies . In some cases (always under the supervision of a doctor), the allergen is administered directly, for example in drug allergy testing .
The treatment of allergies is mainly based on the following principles:
- avoiding triggers ,
- Preventive measures,
- drugs,
- specific allergen immunotherapy ( SAIT ).
For more information on diagnosis and treatment, see the relevant allergies: pollen allergies , insect sting allergies , animal dander allergies , dust mite allergies , food allergies , allergic contact dermatitis , latex allergies , houseplant allergies , drug allergies, and allergies to the sun .
Related links
- Vít Petrů: Specific allergen immunotherapy for allergies and asthma. Medicína pro praxi 2011, 8(10): 407–409 (the link leads to a PDF file on the medicinapropraxi.cz website, 90 kB)
