The Type IV allergy is the so-called "delayed type response" or "cell-mediated type". These are reactions of immune cells against foreign antigens that sometimes last for days and can show up on the skin, for example. A classic example are contact allergies such as nickel allergies, but transplant rejection also falls into this category.
The classification of the allergy types, to which the 'Type IV allergy heard, in four different subgroups, was published by the scientists Coombs and Gell as early as 1963.
According to the current state of research, this is actually no longer immunologically tenable - but the Coombs and Gell classification is still used today because it is didactically very logical and offers a good insight into the development of allergic reactions. However, one should be aware that it is basically only a pathophysiological model.
Only 24 to 48 hours after contact with the triggering allergen does an inflammatory reaction come about through T cells of the human immune system. The body needs this period of time to process the antigen and initiate the reaction. This is an essential difference to the other types of allergies, which are all triggered in some form by preformed antibodies and therefore occur much faster.
As with type I allergy], however, sensitization is generally also necessary for type IV allergies. Only the second contact with the allergen then leads to a reaction, which is another reason why type IV allergies only appear so late.
The exact pathophysiology behind this immunological response is not yet fully understood. Basically, however, it is a sensible reaction of the human body against foreign substances which the immune system initially considers hostile and tries to ward off.
In the case of contact allergy, for example, substances such as nickel or zinc can irritate the skin and, after a certain period of time, lead to inflammation of the skin with reddening, swelling and pain. About 15 percent of all people are affected by such allergic reactions, which are sometimes mild, but in some cases can also be accompanied by extensive skin reactions.
A type IV allergy also occurs with transplant rejection: A transplanted kidney, for example, is always recognized by the own body as a foreign body and fought heavily. This type IV reaction can only be prevented by suppressing the immune system, which must be carried out with medication in the course of every organ transplant and normally maintained for life.
If you let it run free, 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 kidneys, this would mean that urine production decreases again after a week at the latest, high blood pressure develops and the operated patient stores a lot of fluid in the tissue (edema).
Basically, it is a meaningful reaction of the human body, which is not able to differentiate between pathogens that have penetrated from the outside and organs introduced from the outside. A medical application of type IV allergy is the tuberculosis skin test, also known as the tuberculin test or Mendel-Mantoux test:
To find out whether a patient's immune system has currently or 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 puncture site is assessed: If there is major swelling and reddening, the immune system was aware of the pathogen and it responded with a type IV allergic reaction.
If there is only a slight reddening, the reaction was much weaker and one can assume that the body has not yet had anything to do with tuberculosis. A sensitization to the antigen had therefore not yet taken place.
Type IV allergy, like all other forms of allergy, can lead to serious complications. In this type of allergy, however, no desensitization is possible. This means that once the body has been sensitized to an allergen that reacts via a type IV allergy, the only thing that helps is avoiding contact with this allergen.
Otherwise there is a risk of severe eczema and inflammation. Type IV allergies include allergic contact eczema and drug eczema, which in some cases can lead to serious complications. Transplant rejection in organ transplant patients is also due to this type of allergy. The allergic contact eczema becomes chronic if the allergen in question is not avoided, as there is no desensitization.
If it is not possible to avoid the corresponding trigger, a long path of suffering can result. Employees in various occupational groups such as hairdressers, metal workers, construction workers or dental technicians can therefore develop occupational diseases through constant contact with certain substances, which often lead to occupational disability. In the context of medicinal eczema, the so-called Lyell's syndrome is particularly severe.
In the initial stages, it is characterized by flu-like symptoms. After a few days, the rashes begin, which lead to extensive necrosis (death) of the skin and carry the risk of serious infections. In Lyell's syndrome, immediate emergency medical attention is therefore required to avert potentially fatal sepsis.
If you have a type IV allergy, you must consult a doctor. This disease cannot cure independently, so a doctor is always necessary to alleviate the symptoms of this allergy. The treatment itself then depends on the exact type and severity of the symptoms, so that no general prediction can be made about it. In the case of type IV allergies, the doctor should be consulted if the person concerned suffers from an allergic reaction when touching certain substances.
This can lead to various complaints on the skin, so that those affected suffer from a rash or small blisters on the skin. Furthermore, breathing difficulties often indicate the type IV allergy and must be examined by a doctor to prevent further complications. In serious cases, an emergency doctor should always be called or the hospital should be visited directly. If the type IV allergy is mild, an allergist or a general practitioner can be consulted.
Therapeutic and prophylactic measure against contact allergies of the kind Type IV reaction in the simplest case is to avoid contact. Corresponding watches or bracelets should therefore be avoided by people allergic to nickel. A dermatologist can also try cortisone preparations or similar ointments to combat the symptoms.
A measure against transplant rejection is precautionary immunosuppression before the operation or increasing the dosage if the first signs of rejection appear.
Once the treatment of the acute symptoms has been completed, the determination of the allergenic substances is the focus of medical measures. Depending on the appearance and course of the allergic reaction, some of the triggers can be determined with the help of a targeted allergy test. If the test is unsuccessful, potential allergens can be identified using a diary.
Here the patient enters the exact time of his allergic reactions and the severity of the symptoms over a longer period of time. Based on the successful determination of the allergy triggers, the follow-up care aims to avoid contact with these substances. Patients should therefore check carefully which ingredients are contained in foods or cosmetic products, for example, and resort to alternatives if necessary.
It may be advisable to use protective gloves or clothing when handling cleaning agents. In order to be prepared for the unforeseen or inevitable contact with allergens, appropriate ointments or tablets should be purchased in advance. You can prevent allergic shock from occurring in an acute emergency.
A desensitization, in which the body gradually gets used to contact with the allergens, is not possible with a type IV allergy. If permanent contact with the allergy trigger cannot be avoided for professional reasons, retraining must be considered.
If you have a type IV allergy, contact with the triggering allergens should be avoided in the first place. As long as the body is not consciously exposed to the allergens, there are significantly fewer side effects. However, if allergy symptoms occur, treatment with antiallergic drugs is recommended.
Since the symptoms of type IV allergy occur with a delay, an allergy diary must be kept to precisely determine the symptoms and their causes. Additional information such as physical activity, taking medication or drastic life events can also help to find the trigger for the allergy. As a time-saving alternative, a photo can be taken of every meal. In addition, if you have a type IV allergy, you must ensure that you are sufficiently quiet, especially in situations in which contact with the allergen cannot be avoided.
People who suffer from a pollen allergy can follow the latest pollen reports online. For people who suffer from a food allergy, nutrition books are available, in which the individual names of the ingredients are examined in detail. Depending on the type of allergy, the doctor can put you in touch with the appropriate contact point. Suitable contact points are the German Allergy and Asthma Association. V. and the allergy avoidance interest group.