Hypersensitivity types in 4 minutes

Hypersensitivity reactions
When our immune system gets mad
There are 4 types of hypersensitivity reactions, usually labelled in Latin numbers.

In type 1, the antigen, which is usually external allergens such as pollens or certain food molecules, binds to IgE antibodies attached to the surface of mast cells or basophils.
This antigen-antibody binding induces cascade of intracellular reactions resulted in release of large amount of histamine from the storage vesicles.
The released histamine induces various degrees of allergic reactions.

In hypersensitivity type 2, the antigen is not external allergen floating in the blood, but rather certain molecules attached to external surface of the patient cells.
Binding of IgG or IgM antibodies stimulate cascade of immune reactions result in activations of complement system, natural killers, and macrophages.
Which induce further damage to affected tissues.

In hypersensitivity type 3 the small antigen-antibody complexes float through the blood ad accumulate in various tissues such as joints, glomeruli and blood vessels.
This accumulation triggers the complement system to attack the hot tissues.

Unlike other types, the hypersensitivity reaction type 4 is not antibody mediated but mainly cell mediated immunity.
In this type the T helper cells especially CD4 cells recognise the intracellular antigens such as fungi or mycobacterium tuberculosis.
The stimulated CD4 cells release certain cytokines which activates various immune system components such as phagocytes
The activated phagocytes attack and engulf the affected body-cells.
This table summarize the main differences between the 4 types of hypersensitivity reactions.

Now we have comprehensive overview of the hypersensitivity reactions
At the end of this video me and Dr jehad hammad wish you very happy reading
the narration is read by
Alexandra Daniele
Kings College London KCL University

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