Very small immune responses to self antigens is normal and occur in most people. When these become an exaggerated response, or when tolerance to other antigens breaks down, hypersensitivity reactions can occur.
Can cause severe allergic reactions and even death from food-induced anaphylaxis. There is no current treatment, the disease can only be managed by allergen avoidance or treatment of symptoms.
1. Mast cells (tissue basophils) are the cellular receptors for IgE, which attaches to their outer surface
2. IgE is primarily synthesized in the lymphoid tissue of the respiratory and gastrointestinal tracts
3. Normal immune response is a function of Th1 cells which produce IFN-gamma, but in people with allergies, Th2 cells respond instead and produce IL-3, IL-4, IL-5, IL-9, and IL-13
4. IL-4 and IL-13 are responsible for the final differentiation that occurs in B cells, initiating the transcription of the gene that codes for the epsilon-heavy chain of IgE
5. IL-5 and IL-9 are involved in the development of eosinophils, while IL-4 and IL-9 promote development of mast cells
6. IL-4, IL-9, and IL-13 all act to stimulate overproduction of mucus, a characteristic of most allergic reactions
Sequence of events in immediate (type I) hypersensitivity
1. Introduction of an allergen stimulates Th2 responses and IgE production in genetically susceptible individuals
2. IgE binds to Fc receptors (FcεRI) on mast cells
3. Subsequent exposure to the allergen activates the mast cells to secrete the mediators that are responsible for the pathologic manifestations of immediate hypersensitivity
Occurs when mother has been exposed to fetal blood group antigens that differ from her own, leading to IgG antibodies that cross placenta and destroy fetal RBCs