Type 1 Hypersensitivity Reaction
1. Anaphylaxis
2. Atophy (allergy)
1. Anaphylaxis
Means "without protection"
The reaction can occur within seconds exposure to an allergen.
Allergen binds to IgE on the mast cell or basophils and causes cross- linking of several IgE antibodies.
Causes start release of large amount of chemical from granules with in the cell and produce degranulation.
Causes Anaphylaxis
Main effects of anaphylaxis increase in smooth muscle contraction and increase in the permeability of blood vessels.
For example;
1. Incase of gastrointestinal tract, increased fluid secretion cause diarrhoea and vomiting.
2. In respiratory track, anaphylaxis reaction decrease diameter of airway and increased mucus secretion produces coughing.
3. Increased blood flow and permeability allow more intracellular fluid, causes inflammation and increasing anaphylatic reaction.
Mediators of Anaphylaxis Reaction
There are two types of mediators;
1. Primary mediators
2. Secondary mediators
1. Primary mediators
Chemical released by the granules present in cells during degranulation called primary mediators.
Histamine
Neutrophils
Eosinophiils
Heparin
Enzyme; Damage neighbour cells
Serotonin; Cause capillary dilatation, IV permeability and contraction of smooth muscle.
2. Secondary mediators
Chemicals released by mast cells produce anaphylatic reaction called secondary mediators.
Prostaglandins; vasodilation
Platelet activating factor (vesopermeability) and cytokines (stimulating immune system to fight foreign attack).
Allergens such as nuts, sea food, eggs, insect, venom and some drugs cause anaphylaxis.
Manifestation of anaphylaxis
Depend on species of animals
Amount of shocking dose
Site of injection
Portal of entry of antigen
The manifestation may be local or systemic;
1. Localized anaphylaxis
2. Systemic anaphylaxis
1. Localized anaphylaxis
Atophy, allergy, hay fever (seasonal allergy), asthma
a. Cutaneous anaphylaxis
It is induced by both cutaneous (intradermal) injection of antigen or by ingestion.
Manifestation are;
Wheal and flare reaction (dilation of blood vessel)
Urticaria (skin rash by reaction to food, irritants
Angioneurotic edema; painless swelling under skin, allergy to drugs, foods, pollen.
b. Mucosal anaphylaxis
Application of small dose of antigen on mucosal surface such as;
Skin, conjunctiva, nasal mucosa, respiratory tract, gastroentestinal tract symptoms, rhinorrhea, conjunctivitis and bronchospasm, Dermatitis
2. Systemic anaphylaxis
Observed in hypersensitive individuals by insect strings, injection of foreign or drugs, antibiotics.
For example;
Bronchospasm
Laryngeal edema
Respiratory distress
Systemic anaphylaxis is fatal and may cause death, if not treated with adrenaline immediately.
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