Type I
Type I reactions are immune reactions to allergens. Certain types of white blood cells (mast cells and basophils) and IgE antibodies produced on exposure to an allergen mediate this reaction. IgE antibodies quickly bind to the cell membranes of these white blood cells.
This complex is specific to certain allergens. The reaction is often delayed during the first exposure to an allergen. In subsequent exposures, the reaction progresses more rapidly, and the white blood cells release granules that contain inflammatory molecules like histamine and heparin. These molecules cause symptoms like hives and itching.
A severe type I reaction [1] is known as anaphylaxis and is life-threatening. This is often caused by histamine release into the respiratory and circulatory systems. It can cause the airways to close up and drop blood pressure.
Common type I reactions include [2]:
- Allergic rhinitis (hay fever)
- Bronchial asthma
- Allergic dermatitis
- Food allergies