IMMUNOLOGY- Hypersensitivity Reactions and Histamines Flashcards
What type of hypersensitivty reaction is Myaesthenia Gravis and Grave’s disease?
Type V (antibody dependent cell mediated cytotoxicity)
What is the systemic effect of leukotrienes? (3)
- Bronchoconstriction
- Vasoconstriction
- Increase vascular permeability
–> involved in allergic reactions and inflammation
Where is histamine metabolised and excreted?
metabolised in the liver by histaminase, excreted in the urine
Which type of hypersensitivity reactions does histamine modulate?
Typically Type I hypersensitivity (through H1 receptors)
Where are H1 receptors found? What type of hypersensitivity do they modulate?
Found in bronchial muscle and in the CNS.
Modulate Type 1 hypersensitivity reaction
How are H1 receptors activiated? What type of receptor are they?
G couple protein receptor :
Cetrizine –> activation of phospholipase C –> activation which increases intracellular calcium –> increased vascular permeability and arteriolar dilatation –> smooth muscle contraction, bronchospasm and CNS arousal.
Where are H2 receptors found? How are they activated?
Found in stomach, heart and uterus
Cimetidine –> stimulates adenylyl cyclase and cAMP –> pepsin and gastric acid secrtion –> increased myocardial stroke volume.
Where are H3 receptors found?
Expressed in CNS and mediate neurotransmitter release.
What is the difference between H1 anti-histamines and H2 antihistamines?
H1 antihistamines prevent smooth muscle contraction and vascular permeability caused by histamine, they have a
1) Anti-emetic effect
2) Sedative effect
3) Anti-cholinergic effect
H2 antihistamines decrease gastric acid secretion and inhibit cytochrome p450.
What is the mechanism of action of a mast cell stabiliser?
Inhibits release of histamine and slow-releasing substance of analyphaxis (SRS-A) from mast cells by stabilising their membranes –> they are ineffective once mast cells have degranulated
