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Hypersensitivity | Hypersensitivity Types |

Immunity is considered a protective process however when the immune responsive is exaggerated or inappropriate this is called hypersensitivity.

Hypersensitivity | Hypersensitivity Types |


Hypersensitivity is sometimes also called allergy.

Hypersensitivity is of four types:

  • Mediated Hypersensitivity (Allergy)
  • Hypersensitivity
  • Reaction Immune Complex Hypersensitivity
  • Delayed Hypersensitivity
Read: What is sterilization | 2 types of sterilization

1. Type I Reaction: Mediate Hypersensitivity (Allergy) 

These occur in two forms
  1. Acute, Potentially Fatal systemic form called anaphylaxis.
  2. Chronic, Recurrent, nonfatal typically localised called atopy


This is the classical immediate hypersensitivity reaction. in this the allergen introduced into the body and specific IgE is produced which binds to mast cells and basophils.


Atopy is a condition that has a strong genetic link about 10 - 20% of the populations affected in someway. condition such has hay fever & asthma are dur to atopy. the antigen commonly involved in atopy are usually inhaled e.g pollen, house dust, eaten egg milk.

2. Hypersensitivity 

These reaction involve a combination of IgG antibodies with the antigenic determents on the surface of the cell leading to toxicity or bursting of cell.
E.g: Bursting of red cells caused by anti-red cell antibodies in autoimmune anemias and hemolytic disease of the new born.

3. Immune Complex Hypersensitivity 

Type III reaction occur when complexes of antibody and antigen build up in the circulation or in the tissues and activate the complement through IgM or IgG.

These complex may be deposit at different sites in the body including the kidney, joints, skin and eye.

4. Delayed Hypersensitivity

Type IV hypersensitivity due to cell mediated immune responses by the T helper lymphocytes antibodies do not play a role. they are delayed because they take 2-3 days to occur.
There are two phase of Type IV hypersensitivity.
  1. Sensitive Phase
  2. Effector Phase

Sensitisation Phase:

During this phase the antigen is presented by antigen presenting cell to Th cell.


During this phase the antigen react with this specific Th lymphocytes which various cytokines causing local tissue damage

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