Type 2 Hypersensitivity Reaction and Examples

 An elevated activity of normal immune system that damages the body tissues is known as hypersensitivity. Hypersensitivity, also termed as hypersensitivity reaction refers to inappropriate immune responses (like damaging. discomforting, and sometimes fatal). A pre-sensitised (immune) state of the host initiates hypersensitivity reactions.

Туре 2 Hypersensitivity

The type II hypersensitivity reactions cause tissue or cell damage as a direct result of the actions of antibody and complement.

Mode of Action

The reaction during blood transfusion is an example of type II hypersensitivity reactions. In blood transfusion, reaction occurs between the host antibodies and foreign antigens present on the incompatible transfused blood cells. This reaction mediates cell destruction.

Events Following Initial and Subsequent Exposures to an Allergen Resulting in Sensitisation and Manifestation of Allergic Responses

Antibody-mediated cell destruction occurs through activation of complement system. This increases membrane porosity in foreign cell by forming Membrane Attack Complex (MAC). Cell destruction can also be mediated through Antibody Dependent Cell-Mediated Cytotoxicity (ADCC).

Haemolysis of the donor's erythrocytes occurs in the recipient's blood vessels as a result of faulty cross-matching in which the alloantigen of the donor's erythrocytes react with the serum antibodies of the recipient along with the activated complement.

Biological Effects

1. When the maternal IgG antibodies specific for antigens of foetal blood-group cross the placenta and destroy the erythrocytes of foetus, haemolytic disease occurs in new-born.
2. A haemolytic medical condition affecting the new-borns is erythroblastosis foetalis in which the Rh foetus expresses an Rh+ antigen on its blood cells that the Rh- mother does not express.
3. Drug-induced haemolytic anaemia occurs when some antibiotics (e.g., penicillin, cephalosporin and streptomycin) get non-specifically absorbed to proteins on erythrocyte membranes and form a complex (like hapten-carrier complex) that induces anaemia.

Examples of Type 2 Hypersensitivity 

• Autoimmune haemolytic anaemia
• Goodpasture syndrome, 
• Erythroblastosis foetalis pemphigus, 
• Pernicious anaemia (if autoimmune), 
• Immune thrombocytopenia,
• Transfusion reactions, 
• Hashimoto's thyroiditis, 
• Graves' disease, 
• Myasthenia gravis, 
• Rheumatic fever, and haemolytic disease of the new-born. 
• Hyper acute graph rejection.