The type IV allergy is thereby the so-called “reaction of the delayed type” or also of the “cell-mediated type”. It involves reactions of immune cells to foreign antigens, sometimes lasting for days, which can show up on the skin, for example. Classic examples are contact allergies such as nickel allergy, but transplant rejections also belong to this category.
What is type IV allergy?
The classification of allergy types, which includes ‘Type IV allergy, into four different subgroups was published by scientists Coombs and Gell back in 1963. According to the current state of research, this is actually immunologically no longer tenable – nevertheless, the Coombs and Gell classification is still used today, because it is didactically very logical and provides a good insight into the development of allergic reactions. However, one should be aware that it is basically only a pathophysiological model.
Causes
It is not until 24 to 48 hours after contact with the triggering allergen that the inflammatory reaction by T cells of the human defense system occurs. This is the time period required by the body to process the antigen and initiate the reaction. This is a significant difference from the other types of allergy, which are all initiated in some form by preformed antibodies and therefore occur much more quickly. However, just as with type I allergy], type IV allergy generally requires sensitization. Only the second contact with the allergen then leads to a reaction, which is another reason why type IV allergies occur so late. The exact pathophysiology behind this immunological reaction is not yet fully understood. However, it is basically a sensible reaction of the human body against foreign substances that the immune system initially considers hostile and tries to fight off.
Typical symptoms and signs
- Contact allergy (contact dermatitis)
- In transplantation graft rejection
- Papules, vesicles
- Erythema
- Asthma, neurodermatitis
- Stevens-Johnson syndrome
Diagnosis and course
In contact allergy, for example, substances such as nickel or zinc can irritate the skin, and after the appropriate period of time lead to inflammation of the skin with redness, swelling and pain. About 15 percent of all people are affected by such allergic reactions, which are sometimes mild, but in some cases can be accompanied by extensive skin reactions. Type IV allergy also occurs in transplant rejection: A transplanted kidney, for example, is always recognized by the patient’s own body as a foreign body and massively fought against. This type IV reaction can only be prevented by suppressing the immune system, which is carried out with medication as part of every organ transplant and usually has to be maintained for life. If it is given free rein, it leads within a few days to the invasion of T cells into the transplanted organ and to the destruction of this organ. In the case of the kidney, this would mean that urine production would decrease again after a week at the latest, high blood pressure would develop and the operated patient would store a lot of fluid in the tissue (edema). Basically, this is a sensible reaction of the human body, which is not able to distinguish between pathogens invaded from the outside and organs brought in from the outside. One medical application of type IV allergy is the tuberculosis skin test, also called the tuberculin test or the Mendel-Mantoux test:
To find out whether a patient’s immune system is currently or has in the past had to deal with tuberculosis pathogens, the doctor injects tuberculin, a component of killed tuberculosis bacteria, under the skin. After two to three days, the injection site is assessed: If there has been major swelling and redness, the immune system was aware of the pathogen and has responded with a type IV allergic reaction. If there is only a small reddening, the reaction was much weaker and it can be assumed that the body has not yet had anything to do with tuberculosis. Thus, sensitization to the antigen had not yet occurred.
Complications
Type IV allergy, like all other forms of allergy, can lead to severe complications.However, hyposensitization is not possible with this type of allergy. This means that once the body has been sensitized to an allergen, which reacts via a type IV allergy, the only thing that helps is avoiding contact with this allergen. Otherwise there is a risk of sometimes severe eczema and inflammation. In the case of type IV allergy, allergic contact eczema and drug eczema occur, among other things, which in some cases lead to severe complications. Transplant rejection in organ transplant patients is also due to this type of allergy. Allergic contact dermatitis becomes chronic if the allergen in question is not avoided, in the absence of hyposensitization. If it is not possible to avoid the relevant trigger, a long course of suffering may result. Employees in various occupational groups, such as hairdressers, metal workers, construction workers or dental technicians, may therefore develop occupational diseases as a result of constant contact with certain substances, which often lead to occupational disability. In the context of drug eczema, the so-called lyell syndrome shows a particularly severe course. In the initial phase, it is characterized by flu-like symptoms. After a few days, the skin rashes begin, which lead to extensive necrosis (death) of the skin and carry the risk of severe infections. Therefore, in Lyell’s syndrome, immediate emergency medical help is needed to avert potentially fatal sepsis.
When should you see a doctor?
In the case of a type IV allergy, the affected person must see a doctor. There can be no self-healing in this disease, so a doctor is always necessary to relieve the symptoms of this allergy. The treatment itself, however, depends on the exact nature and severity of the symptoms, so that no general prediction can be made. In the case of type IV allergy, the doctor should be consulted if the person concerned suffers from an allergic reaction when touching certain substances. This can cause various symptoms on the skin, so that the affected person suffers from a rash or small blisters on the skin. Furthermore, it is not uncommon for breathing problems to indicate type IV allergy and must be examined by a doctor to prevent further complications. In severe cases, an emergency doctor should always be called or the hospital should be visited directly. For mild manifestations of type IV allergy, an allergist or general practitioner may also be consulted.
Treatment and prevention
Therapeutic and prophylactic measures against contact allergies of the type IV reaction are, in the simplest case, avoidance of contact. Appropriate watches or bracelets should thus be avoided by nickel-allergic people. A dermatologist can also try to combat the symptoms with cortisone preparations or similar ointments. Measure against transplant rejection is precautionary immunosuppression already before the operation or increasing the dosage if the first signs of rejection appear.
Aftercare
Once treatment of the acute symptoms is complete, determination of the allergy-causing substances is the focus of medical measures. Depending on the appearance and course of the allergic reaction, the triggers can sometimes be determined with the help of a targeted allergy test. If the test is unsuccessful, potential allergens can be identified with the aid of a diary. Here, the patient enters the exact time of his allergic reactions as well as the severity of the symptoms over a longer period of time. Once the allergy triggers have been successfully identified, further follow-up care is aimed at avoiding contact with these substances. Patients should therefore check carefully on their own responsibility which ingredients are contained, for example, in food or cosmetic products and, if necessary, resort to alternatives. When handling cleaning agents and detergents, the use of protective gloves or clothing is advisable if necessary. In order to be prepared for unforeseen or unavoidable contact with allergens, appropriate ointments or tablets should be kept in stock. They can prevent the occurrence of an allergic shock in an acute emergency. Hyposensitization, in which the body gradually becomes accustomed to contact with the allergens, is not possible in the case of a type IV allergy.If permanent contact with the allergen cannot be avoided for occupational reasons, retraining must be considered.
What you can do yourself
If a type IV allergy is present, contact with the triggering allergens should be avoided in the first place. As long as the body is not consciously exposed to the allergens, significantly fewer side effects occur. However, if allergy symptoms do occur, treatment with anti-allergic medications is recommended. Since the symptoms of type IV allergy occur with a time lag, an allergy diary must be kept to determine the exact symptoms and their causes. Additional information such as physical activities, the intake of medication or drastic life events can additionally help to find the allergy trigger. As a time-saving alternative, a photo can be taken of each meal. In addition, with a type IV allergy, care must be taken to get enough rest, especially in situations where contact with the allergen cannot be avoided. People suffering from a pollen allergy can follow the latest pollen reports on the web. For people who suffer from food allergies, nutrition books are a good option, in which the individual names of the ingredients are highlighted in detail. Depending on the type of allergy, the doctor can put you in touch with the appropriate contact point. Suitable contact points are, for example, the German Allergy and Asthma Association (Allergie- und Asthmabund e. V.) and the Interest Group for Allergy Prevention (Interessengemeinschaft Allergievermeidung).
