2. Introduction:
• Hypersensitivity: it refers to undesirable reactions
produced by the normal immune system, including
allergies and autoimmunity.
• The term 'allergy' was coined by Clemens von
Pirquet in 1906 .
• The Greek words allos meaning "other" and ergon
meaning "reaction" to describe hypersensitivity
reaction.
• Hypersensitivity in clinical terms is called allergy.
• The substance that triggers allergy is called
allergen(Antigen).
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3. • Most of the allergens are proteins; and their molecular
weight ranges from 10,000-40,000.
• The common allergic disorders are asthma (children's),
allergic rhinitis, anaphylaxis, eczema and urticaria.
National health portal of India:
• Approximately 20% to 30 % of total population(1/3)
in India suffers from at least one allergic disease.
• About 15% develop Asthma and 20% are suffering
with rhinitis.
• Urban children have higher prevalence, About 4.5%
of adolescents are allergic certain food items leading
to asthma, rhinitis or both.
• Developed 7% developing countries shows 10% food
allergies.
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4. Classification:
• Gell and Coomb classified hypersensitivity in the year
of 1963 viz.,
• Type Ⅰ
• Type Ⅱ
• Type Ⅲ
• Type Ⅳ
• First three are mediated by antigen or antigen- antibody
complexes; fourth one cell mediated hypersensitivity.
• All the four involves exaggerated response of their T
cell or B cells.
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5. TYPE 1
HYPERSENSITIVITY
• It is a immediate and humoral
immune response.
Eg: Penicillin
• Components:
a. Allergens
b. Immunoglobulin E
c. Mast cells
d. Basophils
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Haptens: These allergens forms hapten-carrier protein complexes are capable of
eliciting immune response with of IgE , IgM ,and IgG.
6. i. Sensitization:
• Th2 are involved in antigen recognition.
• While interacting with APC Th2 cells produces
specific cytokines viz ., IL-4, IL-5, and IL-3 IL-
33.
• As a result of IL-4, B cells get activates and
differentiate in to plasma cells (IgE).
• These immunoglobulin's shows high affinity
towards Fc↋R1 receptor present on mast cell and
basophile.
• Sensitized mast cell confined to tissues while
basophiles remain in circulation for long time.
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Allergic responses occur in two phases:
7. ii. Degranulation :
• Secondary exposure to an antigen results in cross
linking of IgE molecules with antigen.
• Fc↋RI aggregation causes degranulation of in
basophiles and mast cells.
• The degranulation simply can occur due to
increased influx of Ca++ ions in to mast cells.
• Along with cytoplasmic content primary
mediators are released fallowed by secondary
mediators preparation.
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The biological effect of these mediators are varies; that might cause mild or
severe problems some time death.
Mast cell having other markers also c-kit, CD-34,CD107 etc.
10. Anaphylaxis:
• It is one of the acute and severe allergic reaction to
venom, food, or medication.
• Symptoms:
• Vasodilatation, hypotension, diffulty in breathing ,
swelling under the skin , rashes, nausea, vomiting
etc..
• Treatments:
• Antihistamine, vasoconstrictor, bronchodilator,
Epinephrine etc.
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12. TYPE 2
HYPERSENSITIVITY
• It is characterized by tissue damage.
• Immune system targets tissue-specific antigen.
• It involves 3 main mechanisms:
1. Antibody and complement-mediated destruction.
2. Antibody-dependent cell-mediated cytotoxicity.
3. Target cell disfunction.
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16. Hypersensitivity 16
• There is no cure for this but it is treated with medications and some
times surgery.
• Pyridostigmine stimulates acetylcholine to stimulate receptors.
