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Pregunta:

What are the sequences of events that occur in type 1 Immediate Hypersensitivity?

Autor: Noura Al shalan



Respuesta:

1. In response to certain antigens (allergens), a Th2 and Tfh response is activated. Allergens include pollen, food, insect venom, animal dander, penicillin, causing hay fever, food allergies, bronchial asthma and anaphylaxis. 2. Th2 and Tfh secrete IL-4 and IL-13 that induce switching to IgE production by B cells. IgE bind to mast cells via Fc receptor. (Individual becomes sensitized). 3. On second exposure to allergens, Fc-bound IgE binds to antigens and becomes cross-linked. 4a. Crosslinking of surface IgE causes mast cell degranulation with release of vasoactive amines (histamine) causing immediate hypersensitivity: increase in vascular permeability smooth muscle contraction 4b. Other products released from mast cells include cytokines like IL-4 and TNF- that attract eosinophils and neutrophils causing more severe inflammatory response and tissue injury, called the late-phase reaction.


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1. In response to certain antigens (allergens), a Th2 and Tfh response is activated.  Allergens include pollen, food, insect venom, animal dander, penicillin, causing hay fever, food allergies, bronchial asthma and anaphylaxis.

2. Th2 and Tfh secrete IL-4 and IL-13 that induce switching to IgE production by B cells.  IgE bind to mast  cells via Fc receptor.      (Individual becomes sensitized).

3.  On second exposure to allergens, Fc-bound IgE binds to antigens and becomes cross-linked.

4a. Crosslinking of surface IgE causes mast cell degranulation with release of vasoactive amines (histamine) causing immediate hypersensitivity:
increase in vascular permeability
smooth muscle contraction

4b.  Other products released from mast cells include cytokines like IL-4 and TNF- that attract eosinophils and neutrophils causing more severe inflammatory response and tissue injury, called the late-phase reaction.
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