Hypersensitivity refers to an undesirable reaction of the body's immune system. This reaction may be a kind of allergy or may be the manifestation of an autoimmune condition. Medically, hypersensitivity has been divided into four types:
- Type I hypersensitivity- anaphylactic and atopic
- Type II hypersensitivity- antibody mediated
- Type III hypersensitivity- Immune complex medicated
- Type IV hypersensitivity- delayed or T-cell mediated
Type of hypersensitivity
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Examples
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Type I hypersensitivity- anaphylactic
and atopic
Antigen provokes presensitized mast
cells and basophils through IgE, causing the release vasoactive amines like
histamine. Histamine acts on postcapillary venules.
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Anaphylaxis
Drug allergy
Allergic or atopic conditions like:
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Type II hypersensitivity- antibody
mediated
Antibodies IgM or IgG bind to the
antigen present on the enemy’s cell and trigger lysis or phagocytosis. Three
mechanisms can be explained: opsonizing the cells or activating the
complement system, recruiting neutrophils and macrophages for tissue damage,
and binding to the normal cellular receptors to cause dysfunction.
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Type III hypersensitivity- Immune
complex medicated
Immune complexes provoke complement
system which in turn attacks neutrophils. Neutrophils release lysosomal
enzymes, causing tissue damage.
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Type IV hypersensitivity- delayed or
T-cell mediated
Sensitized lymphocytes encounter/confront
antigens by releasing lymphokines which in turn activate macrophages.
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The table given below describes each type of hypersensitivity with examples:
Keywords: Type I hypersensitivity, Anaphylaxis, Atopic conditions, Type II hypersensitivity, Antibody mediated reaction, Type III hypersensitivity, Immune complex medicated reaction, Type IV hypersensitivity- delayed or T-cell mediated
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