Hypersensitivity reactions Flashcards
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
