Histamines/Hypersensitivity Flashcards
What is an hypersensitive reaction?
An hypersensitive reaction is an unwanted immune response.
Describe Type 1 Hypersensitive reaction. (A)
Anaphlyatic allergic response to allergens, stimulation of B cells via Th2 cells causing the production of IgE antibodies which has increased expression in allergic individuals.
Describe the 2nd type of hypersensitive reaction. (C)
Antibody dependent cytotoxic hypersensitivity attacking non-self cells.
Describe the 3rd type of hypersensitivity reaction. (I)
Complex mediated formation of complexes activates mast cells causing inflammatory mediators to release.
Described the 4th type of hypersensitive reaction. (D)
Cell mediated activation, proliferation and mobilisation of antigen specific T cells and is a delayed response. Cytokines cause leukocytes to go on and cause damage.
What are mast cells and how are they activated?
Mast cells are specialist cells involved in the release of inflammatory mediators and is activated by allergens.
What is the main mediator released by mast cells?
Histamine is the main mediator released.
How does mast cells interacting with allergens cause the release of histamine?
When mast cells interact with allergens, cross links form between IgE antibodies, causing an increase of calcium ions, causing the release of histamine.
What are the 4 histamine receptors and what do they mediate?
H1 inflammatory effects
H2 Gastic acid production
H3 CNS action
H4 immune response regulation
What is the triple response that occurs following the injection of Histamine?
Local oedema occurs due to increasing permeability
Redness occurs at site ( Vasodilation)
Mottled redding around area is caused by arterial dilation.
When released appropriately histamine causes vasodilation why is this useful?
Vasodilation increases blood flow, increases leukocytes delivery, increased venule permeability to allow ease of movement.
What are antihistamines and which hypersensitivity reaction are they effective in?
They are H receptors antagonists blocking histamine action in type 1 hypersensitivity reaction.
How do 1st generation antihistamines differ from 2nd generation antihistamines?
1st generation are non selective and cause sedation by crossing the blood brain barrier and then 2nd generation are selective and don’t cause sedation as they don’t cross the blood brain barrier due to polarity.
