The immune system

Unfortunately, the term “allergy” is often misused today. Not every aversion or reaction to a substance is an allergic reaction. From a medical point of view, allergies are excessive defence reactions of the immune system to substances that actually do not threaten our organism. In order to understand allergies, it is necessary to first understand how the human immune system functions.

Higher beings have mechanisms to differentiate between native and foreign material within their organism. Native material will be tolerated, but foreign material is considered suspicious and triggers defence reactions. The higher the organisms are developed, the more complicated and effective the defence mechanisms become, and the better the immune system learns to tolerate certain “harmless” stimuli and to react against other “menacing” ones.

An essential part of our immune system is memory. The immune system can remember a particular pathogen for years to come and then act more effectively against it in future encounters, which is why you acquire certain diseases which are caused by a specific pathogen only once. One problem for our immune system, however, is pathogens that constantly modify their surface and thus escape detection. A typical example of this is the influenza virus, which appears in a different form every year. The fight against the AIDS virus is also complicated by this circumstance. Vaccinations are used to make the immune system aware of dangerous pathogens. In the process contact takes place between the defence system and a virus or bacterium rendered harmless, the immune response is initiated, and protective antibodies are formed. These antibodies, specific to the pathogen, are found in the blood and in all bodily fluids and can act immediately upon each renewed exposure to the same pathogen. Reproducing these antibodies is much faster and more effective at the second meeting between the respective pathogen and the immune system than at the first contact.

Most allergy triggers are products of nature, such as pollen, food, or pet hair – so, not exactly pathogens! Many important structures of our immune system are located at the surfaces in direct with the outside world, e.g. the mucous membranes of the body’s orifices. At these interfaces to the outside world all foreign substances are subjected to a critical review with regard to their hazardousness. At the same time, the immune system has a difficult task: on the one hand, a liberating, inflammatory defence reaction must take place against all threatening influences (for example, against micro-organisms which can cause diseases, such as bacteria, viruses, fungi, etc.); and on the other hand, no reaction against harmless things should be triggered – but they arrive in our bodies in almost the same manner and are quite similar in their composition. If you take, for example, pollen or the products of dust mites, it can be said that they are very similar to classical pathogens: they are microscopic, protein-rich, and reach the airway via the mucous membranes. Hence, the immune system can mistake a harmless substance for a germ, which can lead to inflammatory defence reactions. The body forms special antibodies against the allergy – so-called IgE antibodies (Immunoglobulin E). The inherited tendency to produce IgE antibodies and, thus, to develop allergies is also called atopy. When IgE antibodies find the right allergen, a chain reaction takes place: explosive release of various mediators that can trigger inflammation – the most important of these inflammatory substances is histamine. This substance triggers a runny nose, itchy eyes, or even an asthma attack. The allergic symptoms typically appear within a few minutes of exposure to an allergy trigger, also known as an immediate allergy.

There are also allergy forms that occur only with delay and after prolonged contact with a substance (delayed patterns of allergy). These often express themselves in persistent rashes. An example of this would be the – very common – nickel allergy.

Allergies often develop slowly. The mechanisms leading to the onset of the allergy are not clear. Unfortunately, it may happen that a cat owner develops an allergy to cat hair only after years. An allergy to pollen can be mistaken at first as a slight itchiness of the eyes which progresses to include slight nasal inflammation. One can easily mistake the symptoms over the course of several years as those of a cold until the patient or a doctor notices that the symptoms seem to increase in intensity from year to year and always seem to appear around the same time of year. The immune system has already developed an allergy, and from the first onset of allergy it is burned into the memory of the immune system. And the immune system has a very good memory! This is an advantage in defending the body against pathogens, but has an adverse effect when it comes to allergies: the immune system will remember having contact with the smallest amounts of an allergen and trigger allergy symptoms upon renewed contact. The hope that hay fever remains a unique event, unfortunately, never comes true. On the contrary, the frequent stimulation of the immune system with the same allergy trigger usually leads to a worsening of the symptoms. Therefore, in the case of a suspected allergy an accurate allergy test should always be performed, because every allergy must be treated.