In Japan patients often say, “I have an allergic diathesis”, or “This disease is caused by an allergy.” The term ‘allergy’ should be taken to mean the specifically altered state of a host following exposure to an allergen. This biological state or allergy has itself either clinical hypersensitivity or clinical immunity. In this report I would like to discuss hypersensitivity. In the case of clinical hypersensitivity, when an antigen enters the body, a circulating antibody will be produced. If the same antigen enters again, the antibody will react to this antigen, and chemical mediators, e.g. histamine, will be released from mast cells. Chemical mediators bring about allergic disorders, such as urticaria or pollinosis (hay fever).
Coombs and Gell classified allergic reactions into four types (I to IV). A Type I reaction is called an immediate type, where an antigen antibody reaction occurs within some tens of minutes. Urticaria, pollinosis (hay fever), asthma, anaphylaxis, and atopy are caused by Type I reactions. Extensive urticaria may be an expression of cutaneous anaphylaxis. Asthma and pollinosis (hay fever) are manifestations of allergic reactions caused by inhaled antigens. The term ‘atopy’ was introduced by Coca in 1929 as a convenient collective term for a group of diseases. Atopy is a genetically determined disorder in which there is an increased tendency to form reagin (IgE) antibodies. Atopic dermatitis and some disorders resulting from insect stings and food allergies are associated with reagin antibodies, and therefore are grouped with the atopic diseases. Some allergic disorders such as pollinosis (hay fever), urticaria, and asthma can occur in any individual who under special circumstances produces reagin antibodies, and who has a familial predisposition to do so. Atopic diathesis is hereditary and it is said that if parents are susceptible to pollinosis or urticaria, their children are likely to suffer from atopic dermatitis or asthma. In the case where an infant simultaneously suffers from atopic dermatitis and asthma, there is a possibility that the asthma will get better as the atopic dermatitis gets worse, and vise versa.
Atopic dermatitis and contact dermatitis, considered to be the most common among the various types of skin diseases, are representative of diseases that result from Type IV reactions. A Type IV reaction is called a delayed type in which an antibody (sensitized lymphocyte) reacts to an antigen after 24-48 hours. Here I would like to emphasize that the dermal symptoms of atopic dermatitis are caused by a Type IV allergic reaction, and that the patient, at the same time, has atopic diathesis with increased production of IgE antibodies which can be attributed to a Type I allergic reaction. The patient with atopic diathesis may possibly react to various stimuli and have strange allergic phenomenon (see next page). This is the reason why atopy is called ‘a strange disease.’
Most allergodermia such as contact or photosensitive dermatitis are due to an antigen antibody reaction with a certain factor, which, having once entered the body later enters it again. This means that these allergic reactions occur as the result of hypersensitivity to a certain substance, not because of an allergic or atopic diathesis.
If you have a comment or question, click here