Hypersensitivity Reaction Types I, II, III, IV

Question 1

Combs and Gell Classification

Answer 1

classification of hypersensitivity reactions through divisions of mechanistically related Ab reactions (and T cell mediated) which contribute to the pathophysiology of the immune-mediated disease.

Question 2

Type I Hypersensitivity

Answer 2

immune reaction against an allergen (innocuous antigen) caused by activation of IgE. Reaction causes an inflammatory response due to the degranulation of mast cells, basophils.
- allergies

Question 3

Type II Hypersensitivity

Answer 3

immune reaction against cell surfaces or extracellular matrix due to the inappropriate targeting of IgG and IgM. leads to effector cell and C’ activation and damaged localized to specific cells of tissue bearing antigen.

• autoimmune hemolytic anemias
• hemolytic disease of newborn (HDNB)
• myasthenia gravis
• transfusion reactions

Question 4

Type III Hypersensitivity

Answer 4

immune reaction against increased amount of ‘soluble’ immune complexes. usually due to persistent infection, autoimmune, or inhalation of Ag, the immune system is unable to clear the increased of large immune complexes leading to inflammation and damage to vascular vessels as it is deposited.

• arthus reaction
• serum sickness

Question 5

Type IV Hypersensitivity

Answer 5

T cell mediated immune response. T cells are sensitized during infection or absorption through epidermis differentiate into effector T cells and activate macrophages leading to local inflammation and edema.

• contact: poison oak/ivy
• tuberculin: tuberculin skin test
• granulomatous: hardening of epithelial cells and macrophages around tissue that cannot be destroyed (Th1 response)