The Body's Response to Allergies and Possible Causes
Normally, the immune system functions as the body's defense against invading germs such as bacteria and viruses. In most allergic reactions, however, the immune system is responding to a false alarm. When a person with allergies first comes into contact with an allergen, the immune system treats the allergen as an invader and gets ready to attack.
The immune system does this by generating large amounts of an antibody called immunoglobulin E, or IgE. Each IgE antibody is specific for one particular substance. In the case of pollen allergies, each antibody is specific for one type of pollen. For example, the immune system may produce one type of antibody to react against oak pollen and another against ragweed pollen.
The IgE molecules are special because they are the only type of antibody that attaches tightly to the body's mast cells (a certain type of tissue cell) and to basophils (a type of blood cell). The next time the allergen encounters its specific IgE, it attaches to the antibody like a key fitting into a lock. This action signals the cell connected to the IgE to release (and in some cases, to produce) powerful chemicals that cause inflammation. Histamine is one of these chemicals. These chemicals act on tissues in various parts of the body, such as the respiratory system, and cause allergy symptoms.
Research scientists do not know for sure why one person develops allergies and another does not. It is believed that allergies originated millions of years ago as a way for the human body to rid itself of parasites and invading worms. Scientists also believe that some people inherit a tendency to be allergic from one or both parents. Children, for example, are more likely to develop allergies if one or both parents have allergies. However, it is unlikely to inherit a tendency to be allergic to any specific allergen.
Being exposed to allergens at times when the body's defenses are lowered or weakened -- such as after a viral infection or during pregnancy -- also seems to contribute to developing allergies.