Hypersensitivity reactions Flashcards
(14 cards)
Why does hypersensitivity occur?
Due to imbalance in levels of immune effector cells and immune regulators. It can occcur due to issues with negative selection of self-reactive B or T cells.
What are the requirements for hypersensitivity?
Requires first exposure antigen contact where antibodies are produced or immune cells are primed.
What is Type 1 hypersensitivity?
Immediate reaction. IgE binds to antigen and acts on mast cells and basophils for degranulation and release of histamine.
What is the physiological effects of Type 1 hypersensitivty?
Vasodilation which can cause drop in BP/hypotension and redness
Smooth muscle contraction which causes difficulty breathing
Increased vascular permeability that can cause oedema
What are examples of Type 1 hypersensitivity reacitons?
Allergy, asthma, urticaria, Anaphylactic shock, eczema
How is anaphylactic shock treated?
Adrenaline- it binds to B2 receptors to cause vasoconstriction and increase in BP and reduction in vascular permeability
What is Type 2 hypersensitivity
IgG and IgM mediated which binds to cell surface receptors to cause phagocytosis or complement activation. It interferes with cell function.
What are examples of Type 2 hypersensitivty?
Haemolytic disease of the newborn
Autoimmune conditions
-> Myasthenia gravis, immune thrombocytopenia, Goodpasture syndrome, Graves disease
What is Type 3 hypersensitivity?
Immune complex deposition- IgG or IgM binds to free floating antigens. This causes complement system activation.
What are examples of Type 3 hypersensiitivty?
Arthritis, vasculitis, glomerulonephritis, Lupus, serum sickness and arthus reaction
What is Type 4 hypersensitivity?
T cell mediated which is delayed involving Th1 cells and CD8+ T cells. Th1 cause inflammation by activating macrophages and neutrophils. T killer cells have cytotoxic action.
What are examples of Type 4 hypersensitivity reactions?
Contact dermatitis, tuberculosis skin test, coeliac disease
What is serum sickness?
Type 3 hypersensitivity to injection of foregin proteins from drugs like antivenom or antitoxins.
What is immune thrombocytopenia?
Type 2 hypersensitivity autoimmune disease which targets platelets and causes reduction in platelet count
