Hypersensitivity
What is Hypersensitivity.
Basic mechanism of Type I - V hypersensitivities.
Few common example for Type I - V hypersensitivities.
What is Hypersensitivity?
Immune response that damages the body’s own tissues.
Several types – depend on mechanism.
Type I - type V (type VI).
Type I hypersensitivity
IgE mediated.
Called allergy.
Allergic reaction provoked by re-exposure to a specific antigen.
Pollen, mites, drugs, food….
Release of histamine, arachidonate and derivatives from basophils and mast cells.
Develop 15-30 min.
The reaction - local or systemic.
Allergic asthma, Allergic conjunctivitis, Allergic rhinitis, Anaphylaxis.
Allergic tendency
Some people get allergy often.
Called – atopic allergies.
Genetically passed.
High IgE in body.
Type II hypersensitivity
Antigens on the patient’s own cell surfaces.
Ig G & Ig M mediated.
complement activation.
Intrinsic/”self” antigen or extrinsic.
Autoimmune haemolytic anaemia & transfusion reactions.
Type III hypersensitivity
Form immune complex and deposit.
Ig G, Ig M, Ig A mediated.
complement activation.
Examples
Immune complex glomerulonephritis
Rheumatoid arthritis
Serum sickness
Subacute bacterial endocarditis
Type IV hypersensitivity
Delayed type - two to three days to develop.
Cell medicated.
Macrophages activated and release chemicals.
Contact dermatitis, transplant rejection.
Type V & VI hypersensitivity
Type V - Cell surface receptors destroyed (not whole cell like type II)
Graves’ disease
Myasthenia gravis
Type VI – antibody dependent cell mediated cytotoxicity.