With Excess IgE Antibodies

Some people have an “allergic” tendency. Their allergies are called atopic allergies because they are caused by a nonordinary response of the immune system. The allergic tendency is genetically passed on from parent to child and is characterized by the presence of large quantities of IgE antibodies. These antibodies are called regains or sensitizing antibodies to distinguish them from the more common IgG antibodies. When an allergen (defined as an antigen that reacts specifically with a specific type of IgE regain antibody) enters the body, an allergen-reagin reaction takes place and a subsequent allergic reaction takes place.

A special characteristic of the IgE antibodies (the regains) is a strong propensity to attach to mast cells and basophils. Indeed, a single mast cell or basophil can bind as many as half a million molecules of IgE antibodies. Then, when an antigen (an allergen) that has multiple binding sites binds with several of the IgE antibodies attached to a mast cell or basophil, this causes an immediate change in the membrane of the cell, perhaps resulting from a simple physical effect of the antibody molecules being pulled together by the antigen. At any rate, many of the mast cells and basophils rupture; others release their granules without rupturing and secrete additional substances not already preformed in the granules. Some of the many substances that are either released immediately or secreted shortly thereafter include histamine, slow-reacting substance of anaphylaxis (which is a mixture of toxic leukotrienes), eosinophil chemotactic substance, a protease, a neutrophil chemotactic substance, heparin, and platelet activating factors. These substances cause such phenomena as dilatation of the local blood vessels, attraction of eosinophils and neutrophils to the reactive site, damage to the local tissues by the protease, increased permeability of the capillaries and loss of fluid into the tissues, and contraction of local smooth muscle cells. Therefore, a number of different types of abnormal tissue responses can occur, depending on the type of tissue in which the allergen-reagin reaction occurs. Among the different types of allergic reactions caused in this manner are the following:

Anaphylaxis. When a specific allergen is injected directly into the circulation, it can react in widespread areas of the body with the basophils of the blood and the mast cells located immediately outside the small blood vessels if these have been sensitized by attachment of IgE regains. Therefore, a widespread allergic reaction occurs throughout the vascular system and in closely associated tissues. This is called anaphylaxis. The histamine released into the circulation causes body-wide vasodilatation as well as increased permeability of the capillaries with resultant marked loss of plasma from the circulation. Many people who experience this reaction die of circulatory shock within a few minutes unless they are treated with epinephrine to oppose the effects of the histamine. But also released from the cells is a mixture of leukotrienes, which are also called slow-reacting substance of anaphylaxis. These leukotrienes cause spasm of the smooth muscle of the bronchioles, eliciting an asthma-like attack and sometimes causing death by suffocation.

Urticaria. Urticaria results from antigen entering specific skin areas and causing localized anaphylactoid reactions. Histamine released locally causes (1) vasodilatation that induces an immediate red flare and (2) increased local permeability of the capillaries that leads to local circumscribed areas of swelling of the skin in another few minutes. The swellings are commonly called hives. Administration of antihistamine drugs to a person before exposure will prevent the hives.

Hay Fever. In hay fever, the allergen-reagin reaction occurs in the nose. Histamine released in response to the reaction causes local vascular dilatation, with resultant increased capillary pressure, as well as increased capillary permeability. Both of these effects cause rapid fluid leakage into the tissues of the nose, and the nasal linings become swollen and secretory. Here again, use of antihistamine drugs can prevent this swelling reaction. Other products of the allergen-reagin reaction still cause irritation of the nose, still eliciting the typical sneezing syndrome despite drug therapy.

Asthma. Asthma often occurs in the “allergic” type of person. In these, the allergen-reagin reaction occurs in the bronchioles of the lungs. Here, the most important product released from the mast cells seems to be the slow-reacting substance of anaphylaxis, which causes spasm of the bronchiolar smooth muscle. Consequently, the person has difficult breathing until the reactive products of the allergic reaction have been removed. Administration of antihistaminics has little effect on the course of asthma because histamine does not appear to be the major factor eliciting the asthmatic reaction.

31. Revision questions:

1. What items most often trigger asthma in susceptible people?

2. How do allergy shots work?

3. How many gene combinations are most common for Europeans?

4. What patients are most at risk of allergic responses?

5. What can be an allergen?

6. What allergies are called atopic allergy?

7. What is called anaphylaxis?

8. What does the histamine cause?

9. What does urticaria result from?

10. Where does the allergen-reagin reaction occur in case of hay fever?

11. Has the person difficulty with breathing while asthma attack?

12. Is it better to treat or to prevent allergy?