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- Allergy facts
- Allergy overview
- What is an allergy?
- What is an allergy? (Continued)
- What causes allergies?
- What causes allergies? (Continued)
- Who is at risk for allergies and why?
- What are common allergic conditions and what are allergy symptoms and signs?
- Allergic rhinitis (hay fever)
- Allergic eyes (conjunctivitis)
- Eczema (atopic dermatitis)
- Hives (urticaria)
- Allergic shock (anaphylaxis)
- Where are allergens?
- In the Air We Breathe
- In What We Ingest
- Touching Our Skin
- Injected into Our Body
What causes allergies? (Continued)
In the pet cat example, the dad and the youngest daughter developed IgE antibodies in large amounts that were targeted against the cat allergen. The dad and daughter are now sensitized or prone to develop allergic reactions on subsequent and repeated exposures to cat allergen. Typically, there is a period of "sensitization" ranging from days to years prior to an allergic reaction. Although it might occasionally appear that an allergic reaction has occurred on the first exposure to the allergen, there needs to be prior contact in order for the immune system to be poised to react in this way. It is important to realize that it is impossible to be allergic to something that an individual has truly never been exposed to before, though the first exposure may be subtle or unknown.
IgE is an antibody that all of us have in small amounts. Allergic individuals, however, generally produce IgE in larger quantities. Historically, this antibody is important in protecting us from parasites. During a sensitization period, cat dander IgE is overproduced and coats certain potentially explosive cells, such as mast cells and basophils that contain various mediators, such as histamine. These cells are capable of leading to an allergic reaction on subsequent exposures to allergen, which is the cat protein in this example. The cat protein is recognized by the IgE leading to activation of the cells, which leads to the release of various chemicals, including histamine. These chemicals, in turn, cause localized swelling, inflammation, itching, and mucus production, all of which are typical allergic symptoms. Once primed, or sensitized, the immune system is capable of mounting this exaggerated response with subsequent exposures to the allergen.
On exposure to cat dander, whereas the dad and daughter produce IgE, the mom and the other two children produce other classes of antibodies, which do not cause allergic reactions. In these nonallergic members of the family, the cat protein is eliminated uneventfully by the immune system and the cat has no effect on them.