Hypersensitivity. Allergies
The function of the immune system is to destroy foreign antigens without causing any harm to the person, but, on occasions, these responses can be of excessive force in the face of harmless or not very dangerous molecules, and can produce serious effects on people, even death.
Two types of hypersensitivity are distinguished:
The allergy is a hypersensitivity mechanism or exaggerated immune response to the presence of antigens safe or very dangerous.
The immediate or anaphylactic hypersensitivity develops rapidly, about 10 to 20 minutes after exposure to the antigen, which in this case is called allergen.
An allergen is a substance that induces a hypersensitivity (allergic) reaction in susceptible people who have previously been in contact with them. Some of the most common allergens are bee venom, pollen proteins, animal hair, dust mite feces, some medications like penicillin, some foods like shellfish, peanuts, etc.
Development of the allergic reaction
The allergic reaction develops following these phases:
1.- Allergen uptake by antigen presenting cells.
2.- Sensitization to the allergen.
When the first contact with the allergen occurs, no external symptoms are shown, but the immune system recognizes the allergen since the antigen-presenting cells (APCs) phagocytize it and show its fragments in the MHC-II to the helper T lymphocytes (TH), which recognize and activate neighboring B lymphocytes. The B lymphocytes into plasma cells and release large amounts of IgE immunoglobulins which bind to the constant region of basophils blood and mast cells tissues. This is the process of awareness raising.
3.- Release of the content of the histamine-filled mast cell granules.
When the second contact with the allergen occurs, the allergic reaction occurs. The allergen binds to the IgE that coat mast cells and basophils, causing their degranulation, expelling substances from the cell cytoplasm. These secreted substances cause inflammation (histamines, prostaglandins, serotonin, etc.) and allergy discomfort, such as dermatitis or diarrhea, if it is a food allergy, mucus secretion if it is an allergy caused by substances contained in the air, etc. If mast cells and basophils discharge histamineblood, dilation will causes blood vessels, leading to a generalized reaction, with the contraction of the bronchioles and generally vasodilation can cause death by asphyxiation or a significant decrease in the blood pressure (anaphylactic shock).