Type I allergy is a group of different allergic hypersensitivity reactions of the human body. The classification of the type is thereby based on the classification of Coombs and Gell into four different types. According to current knowledge, this classification is immunologically outdated, but it is still maintained and taught in medicine for didactic reasons.
What is type I allergy?
Type I reaction is the “classic” allergic reaction, the “immediate type,” in which allergens such as pollen or animal dander trigger a release of messenger substances within seconds to minutes via binding to specific antibodies on so-called mast cells of the mucous membranes. This subsequently leads to the typical allergic symptoms such as swelling of the mucous membranes, sneezing, itching and eye redness, asthmatic attacks or, in the worst case, a drop in blood pressure and life-threatening anaphylactic shock reactions.
Causes
Triggers of such a reaction are usually large molecules, such as pollen, protein, drugs, contrast media, or insect venoms. Normally, the body’s reaction to an antigen is a sensible thing to do, because it allows viruses and bacteria to be recognized and warded off as quickly as possible. In the case of allergies, however, this defense strategy of the body is out of control: The body reacts to substances that are harmless in themselves as if they were pathogens. This first requires sensitization: Upon initial contact with the antigen, nothing major happens at first. At the cellular level, however, the antigen is recognized as foreign, slowly processed, and the body builds mast cells into its mucous membranes that are specialized only to trigger an immediate defensive action the next time the same antigen appears. If, after such sensitization, a second contact occurs, these specialized mast cells release massive and completely exaggerated amounts of messenger substances, which then trigger the symptoms described at the beginning. In addition to this immediate response, the type I reaction also includes a late response that begins after several hours, can last for days, and consists of tissue infiltration with inflammatory cells.
Symptoms, complaints, and signs
Allergy can cause various symptoms of varying intensity. These extend either to individual parts of the body or to the entire organism. When an allergy occurs, it usually belongs to type I. A good 90 percent of all cases can be attributed to it. Signs appear immediately, after a few minutes or hours. The most frequent complaints concern the skin and the respiratory tract. The skin is reddened or a rash has formed. Often wheals appear. Affected persons begin to cough. The swollen mucous membranes may even cause respiratory distress. Asthma attacks are possible. The nose, through which breathing also takes place, expels liquid mucus. There is a constant sneezing. The allergic reaction sometimes causes the eyes to redden. An uncontrollable light lacrimation sets in. Some patients even feel that the eyes burn. All the named symptoms represent a defensive reaction of the body. In addition, general signs may accompany a type I allergy. As a result of the reaction, sufferers sometimes complain of sudden fatigue. Headaches and diarrhea may also occur. If the entire organism displays symptoms, caution is advised. In anaphylactic shock, life is threatened.
Diagnosis and course
Type I allergy of the body may remain localized. There is then redness, swelling, formation of wheals on the skin with itching. If the respiratory tract is affected, as in pollen allergy (hay fever), there is rhinitis, sneezing, swelling of the airways. If the whole thing happens one floor lower, the swelling of the bronchial tubes can also trigger an asthma attack. For example, hay fever can worsen over the course of years and turn into asthma (“floor change”). If the reaction is not local, for example after systemic administration of drugs or contrast media, the type I reaction can also occur throughout the body and then primarily affects the bloodstream. Initiated by the mediators released, blood vessels are dilated throughout the body, blood pools in the legs, is absent from the brain, and the affected person becomes unconscious.This severe drop in blood pressure leads to a life-threatening lack of oxygen in the brain and internal organs and is known as “anaphylactic shock“. It can also occur, for example, if you are stung by a wasp, have an allergic reaction and then faint. Emergency medical treatment is then vital. The doctor usually recognizes the allergic cause of an emergency from the medical history. It is therefore important to be able to give reasonable information about the circumstances under which a hay fever, skin redness, asthma attack or, in the worst case, fainting occurred.
Complications
Type I allergy, the most common type of allergy, is characterized by typical inflammatory reactions immediately after allergen contact. In most cases, no complications occur. When allergen contact is stopped, the inflammatory reactions usually subside quickly. However, in a few cases, these immune reactions can become so severe that even life-threatening complications occur. The main complications of type I allergy are allergic asthma and anaphylactic shock. Allergic asthma, like other forms of asthma, can become a life-threatening emergency in extreme cases. Severe asthma is characterized by severe shortness of breath, overinflated thorax, cyanosis (bluish discolored lips due to lack of oxygen), exhaustion or even confusion. Coughing and palpitations always occur. Respiratory distress may become so severe that the patient’s life is acutely threatened. Anaphylactic shock is always a life-threatening crisis that requires immediate treatment. It is a circulatory shock caused by massive vasodilatation. Blood pressure drops very sharply and the pulse is barely palpable. However, the heart rate increases extremely to compensate. Volume replacement therapy must be given immediately to save life. Drug therapy can be given by using adrenaline, among other drugs. If possible, the triggering allergen should be removed immediately. In both allergic asthma and anaphylaxis, symptoms resolve rapidly after interruption of allergen contact.
When should you see a doctor?
The affected person should always consult a doctor in case of type I allergy. Since this disease cannot be cured on its own and the symptoms usually significantly restrict the life of the affected person, the disease must always be controlled by a medical professional. A complete cure is not always possible, although the symptoms can be significantly alleviated. As a rule, the doctor should be contacted if the affected person suffers from severely reddened skin or if there is a severe rash on the skin. These complaints usually occur when the affected person comes into contact with or ingests a certain substance. Furthermore, burning eyes or breathing difficulties can also indicate type I allergy. Many patients also suffer from diarrhea or severe headaches. Type I allergy can be recognized relatively easily by a general practitioner or by an internist. Further treatment depends on the cause and also on the severity of the symptoms, so that no general prediction is possible in this case.
Treatment and therapy
Therapeutically, there are various measures against type I allergies: purely symptomatic, one can take so-called antihistamines, which prevent the release of the messenger substances involved. This works better in some patients and worse in others. Emergency sprays that actively dilate the bronchial tubes after inhalation help against asthma attacks. This works very well for most asthmatics. In more serious emergencies, an emergency physician always has so-called glucocorticoids in his luggage, e.g. cortisol, which can be injected into the vein and slow down the body’s entire defensive reaction, which has gotten out of hand. In addition to these purely symptomatic measures, there is also the long-term option of hyposensitization therapy. By slowly increasing the amount of the triggering antigen over a period of months, an attempt can be made to accustom the body to the substance and at the same time to wean it off the allergic reaction. With some allergies, such as hay fever, this often works well, with others, such as animal hair, only rarely.
Prevention
In terms of prevention, there are various theories: What is certain is that each person has a differently pronounced tendency to allergic type I reactions. If both parents are asthmatics, the risk of having asthma attacks themselves is significantly higher than in the “normal population.” 10% of all people in Germany have such type I allergies, so the word “normal population” is put in quotation marks here. In children, the percentage is even higher. At the same time, however, you can do your children some good if you let them come into contact with dirt: The so-called “hygiene hypothesis” states that children who grew up on farms and played outside a lot are significantly less likely to develop allergies than children from inner-city households. Thus, too much hygiene increases the risk of type I allergy.
Follow-up
Initial treatment usually addresses only the symptoms of a type I allergy. In many cases, however, targeted aftercare in the form of hyposensitization or specific immunotherapy (SIT) can be useful. In this way, the allergy is treated in the long term. In the course of hyposensitization, the allergy sufferer’s immune system is gradually accustomed to the substances that are responsible for the occurrence of the type I allergy. Hyposensitization is so far considered the only way to act against the causes of allergy. Specific immunotherapy makes it possible to improve the symptoms and prevent secondary diseases. Often, allergy sufferers can even be permanently freed from the symptoms of the allergy. As a rule, however, it is only effective in the case of a type I allergy. It must therefore be an allergy of the immediate type. During the follow-up treatment, the allergy sufferer is administered the allergen that causes the allergic reactions at regular intervals. As the treatment progresses, the dose increases. Specific immunotherapy is divided into an initial phase and maintenance therapy. During the initial phase, the patient receives an injection of an allergen extract under the skin every week. If the dose is eventually tolerated, maintenance therapy begins, during which the highest possible dose is injected once a month. As a rule, classical immunotherapy takes up to three years.
