Hypersensitivity Flashcards
What is type I hypersensitivity?
Allergic reaction
Contact with antigen
Mast cells bund IgE with Fc receptors
IgE bceomes cross linked on encountering antigen
Mast cell degraulation
Release of histamine, serotonin, platelet activating factos, eosinophil chemotactic factors
Histamine exerts negative feedback to inhibit mast cell degranulation
What is type II hypersenitivity?
Antibody-dependent
Antibody directed against cell surface or tissue antigens (expressed by own cells)
Phagocytes release lysosomal contents causign tissue damage
What are examples of type II hypersensitivty
Rhesus disease of newborn (IgG against RhD antigen is produced by rhesus negative mothers and crosses placenta to attack rhesus positive fetus
ABO incompatibility
Hyperacute graft rejection
Myasthenia gravis
What are type III hypersenstivity reactions?
Immune complex - deposited in tissues
stimulate complement - acute infalmmation
Turbulent blood flow allowing for deposition of immune complees
Increased vascular permeability due to histamine release
Specific antigen-antibody complexes to a single organ
Wha are examples of type III
Ciral hepatitis - perisistent infection
Autoimmune disease - RA, SLE
Arthus reaction - injection of antifen in individuals who has previously been exposed and have high antibody levels - complex is deposited causing acute inflammation
Peaks at 4-10h
What is Type IV hypersensitivty
Cell mediated
Antigen sensitised T cells release cytokines following a second contact
Cytokines induce inflammation and attract and activate macrophages
Take more than 12 hours to develop
What are examples of type IV
Contact hypersensitivity by an epidermal reaction via Langerhan’s cells
Tuberculin type - casued by subdermal injection of tuberculin producing a reaction in the dermis (Mantoux test) 48-72h
Cell mediated - results in granulomarous reaction and is usually caused by a persistent antigen in macrophages
Giant papillary conjunctivitis, vernal keratoconjucntivitis, atopic keratoconjunctivitis
