Hypersensitivity-Anaphylaxsis

Hypersensitivity-Anaphylaxsis:

Definition:

Type I hypersensitivity reactions are started by antigens reacting with cell bound antibody generally IgE. IgE is termed as reaginic antibody. IgE antibodies are cytotropic antibodies since they are fixed on the surface of tissue cells like basophils and mast cells. The antigen joins with the cell fixed antibody leading to discharge of pharmacologically active substances (i.e., vasoactive amines) that generate clinical reaction.

A) Clinical syndromes of Type I hypersensitivity are Atopy and Anaphylaxis.
B) Anaphylaxis (i.e., Ana-without; prophylaxis-protection)

Anaphylactic hypersensitivity can be passively shifted from a sensitive donor to a common recipient by injection of serum. It is caused by IgE (i.e., reaginic antibody).

Mechanism of anaphylaxis:

IgE antibody is a cytotropic antibody. It contains affinity for mast cells and basophils. Therefore it will be attached on the surface of basophils and mast cells. Whenever an allergen enters it will cross link to antibody molecules which are attached to the membrane of the mast cells. This causes an influx of Ca2+ and a reduce in the level of CAMP. As an outcome of this, degranulation of mast cells takes place and primary and secondary mediators of anaphylaxis are discharged. Primary mediators are serotonin, histamine, and secondary mediators are prostaglandin and platelet activating factor. Such mediators cause various types of anaphylaxis.

1088_mast cell.jpg

Figure: Mast Cell

Types of Anaphylaxis:

Anaphylaxis is classified as follows:

1. Cutaneous anaphylaxis
2. Passive cutaneous anaphylaxis
3. Anaphylaxis invitro

 

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