Type IV allergy is the so-called “delayed type reaction” or “cell-mediated type”. These are reactions of immune cells to foreign antigens, which can show up on the skin, for example, and sometimes last for days. Classic examples are contact allergies such as nickel allergy, but transplant rejection also belongs in this category.
What is type IV allergy?
The classification of allergy types, which also includes type IV allergy, into four different subgroups was published by the scientists Coombs and Gell as early as 1963. For what does the abbreviation ks stand for, please visit usvsukenglish.com.
According to the current state of research, this is no longer immunologically tenable – nevertheless, the Coombs and Gell classification is still popular 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 just a pathophysiological model.
Only 24 to 48 hours after contact with the triggering allergen does the T-cells of the human immune system trigger an inflammatory reaction. The body needs this time to process the antigen and initiate the reaction. This is a major difference to the other types of allergies, which are all triggered in some way by preformed antibodies and therefore occur much more quickly.
Just as with type I allergy ], however, type IV allergy generally also requires sensitization. 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 fully understood. Basically, however, it is a sensible reaction of the human body against foreign substances, which the immune system initially considers to be hostile and tries to ward off.
Typical Symptoms & Signs
- Contact allergy (contact dermatitis)
- in transplants transplant rejection
- papules, vesicles
- asthma, neurodermatitis
- Stevens-Johnson Syndrome
Diagnosis & History
In the case of contact allergies, for example, substances such as nickel or zinc can irritate the skin and, over time, lead to skin inflammation 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 widespread skin reactions.
A type IV allergy also occurs when a transplant is rejected: a transplanted kidney, for example, is always recognized by the body as a foreign body and is massively combated. 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 allowed to run wild, within a few days, T cells will invade and destroy the transplanted 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 ( oedema ).
Basically, it is a sensible reaction of the human body, which is not able to distinguish between externally introduced pathogens and externally introduced organs. A medical application of type IV allergy is the tuberculosis skin test, also called tuberculin test or Mendel-Mantoux test:
To find out whether a patient’s immune system has had to deal with tuberculosis pathogens now or in the past, the doctor injects tuberculin, a component of dead tuberculosis bacteria, under the skin. The puncture site is assessed after two to three days: if there is significant swelling and redness, the immune system was aware of the pathogen and responded with a type IV allergic reaction.
If there is only a little reddening, the reaction was much weaker and one can assume that the body has not yet had anything to do with tuberculosis. Sensitization to the antigen had therefore not yet taken place.
Like all other forms of allergy, type IV allergy can lead to severe complications. However, hyposensitization is not possible with this type of allergy. This means that once the body has become sensitized to an allergen, which reacts via a type IV allergy, the only solution is to avoid 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 lead to serious 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, since hyposensitization does not take place.
If it is not possible to avoid the corresponding trigger, a long ordeal can result. Employees in various occupational groups such as hairdressers, metalworkers, 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 drug eczema, the so-called Lyell’s 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, leading to extensive necrosis (death) of the skin and harboring the risk of serious infections. Immediate emergency medical attention is therefore required in Lyell’s syndrome to avert potentially fatal sepsis.
When should you go to the doctor?
If you have a type IV allergy, you need to see a doctor. This disease cannot heal on its own, so a doctor is always necessary to alleviate the symptoms of this allergy. However, the treatment itself depends on the exact type and severity of the symptoms, so that no general prediction can be made. In the case of type IV allergies, the doctor should be consulted if the person affected suffers from an allergic reaction when touching certain substances.
Various complaints can occur on the skin, so that those affected suffer from a rash or small blisters on the skin. Furthermore, it is not uncommon for breathing difficulties to indicate the type IV allergy and must be examined by a doctor in order to prevent further complications. In serious cases, you should always call an ambulance or go straight to the hospital. If the type IV allergy is mild, an allergist or a general practitioner can also be consulted.
Treatment & Prevention
In the simplest case, avoidance of contact is a therapeutic and prophylactic measure against contact allergies of the type IV reaction . Corresponding watches or bracelets should therefore be avoided by people allergic to nickel. A dermatologist can also try to combat the symptoms with cortisone preparations or similar ointments.
Measures against transplant rejection are preventive immunosuppression before the operation or an increase in 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 the 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 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, further follow-up care is aimed at avoiding contact with these substances. Patients should therefore check on their own responsibility which ingredients are contained in food or cosmetic products, for example, and use alternatives if necessary.
When handling cleaning agents, it may be advisable to use protective gloves or clothing. In order to be prepared for the unforeseen or unavoidable contact with allergens, appropriate ointments or tablets should be purchased in advance. They can prevent an allergic shock from occurring in an acute emergency.
Hyposensitization, 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 work-related reasons, retraining must be considered.
You can do that yourself
If a type IV allergy is present, the first priority should be to avoid contact with the triggering allergens. As long as the body is not consciously exposed to the allergens, there are significantly fewer side effects. Should allergy symptoms nevertheless occur, treatment with antiallergic medication is recommended.
Since the symptoms of type IV allergies occur with a time lag, an allergy diary must be kept in order 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 allergy trigger. As a time-saving alternative, a photo can be taken of each meal. In addition, people with type IV allergies need to get enough rest, especially in situations where exposure to the allergen is unavoidable.
People suffering from a pollen allergy can follow the current pollen count reports online. For people who suffer from a food allergy, there are books on nutrition that detail the individual names of the ingredients. Depending on the type of allergy, the doctor can establish contact with the appropriate contact point. Suitable contact points include the German Allergy and Asthma Association. V. and the allergy prevention interest group.