Chemical mediators Flashcards
What is meant by the term inflammatory mediators?
they are substances that initiate and regulate inflammatory reactions
- Can be produced locally (at the site of inflammation, or from circulating inactive precursors “from the liver” which are activated at the site of inflammation)
- Acts by binding to specific receptors
Where are cell-derived mediators of inflammation?
1) Sequestered in cells (intracellular granules), like histamine in mast cells
2) De Novo synthesis in response to stimulus, (like prostaglandins, cytokines, arachidonic acid metabolites, etc)
How are active mediators produced?
- In response to various molecules that stimulate inflammation (like microbial products, & substances released from necrotic cells (host proteins), they are mostly short-lived (preventing chronic inflammation) and can stimulate the release of other mediators)
What are the different biological activities of activated mediators?
1) Binds to specific receptors on target cells
2) Direct enzymatic activity (lysosomal proteases, complement system)
3) Mediates oxidative damage (ROS & nitrogen intermediates)
What is the source and action of Histamines (vasoactive amine)?
1) Mast cells
2) Basophils
3) Platelets
- Released in response to (physical injury, antibody binding to mast cell granules (type 1 hypersensitivity, and also to the products of complement “anaphylatoxins” C3a & C5a)
- Vasodilation, Increases vascular permeability and activates endothelial cells, causing wheal and flare reaction of the skin, mediated by binding to receptor (H1 receptors) on microvascular endothelial cells
What is the source and action of Prostaglandins?
1) Mast cells
2) Leukocytes
- Vasodilation, pain, fever
What is the source and action of Leukotrienes?
1) Mast cells
2) Leukocytes
- Increased vascular permeability, chemotaxis, leukocyte adhesion and activation
What is the source and action of the platelet-activating factor?
1) Mast cells
2) Leukocytes
- Vasodilation, Increased vascular permeability, leukocyte adhesion, chemotaxis, degranulation, oxidative burst
What is the source and action of chemokines?
1) Activated mast cells
2) Leukocytes
- Chemotaxis & leukocyte activation
What is the source and action of Cytokines (TNF, IL-1, IL-6)?
1) Mast cells
2) Macrophages
3) Endothelial cells
- Local, endothelial activation (expression of adhesion molecules)
- Systemic, fever, metabolic abnormalities, hypotension (shock)
What is the source and action of COMPLEMENT?
1) Found inactive in plasma (produced in the liver)
How is it activated?
1) Classical: C1 will bind to an antibody (IgM or IgG) along with an antigen, becoming a proteolytic enzyme, activating C2,3,4
2) Alternative: Via LPS and endotoxins
3) Lectin: Or finally plasma mannose-binding lectin which binds to microbial carbohydrates directly activating C1
all of them will activate C3 splitting into C3a (chemotaxis and leukocyte activation “inflammation”, C5a does the same thing) & C3b (opsonization “phagocytosis and MAC formation)
- Leukocyte chemotaxis and activation, direct target killing (MAC), Vasodilation (mast cell stimulation), opsonization
What is the source and action of KININS?
1) Found inactive in plasma (produced in the liver)
- Increases vascular permeability, smooth muscle contraction, vasodilation & pain
Which chemical mediators induce pain
1) Prostaglandins
2) Kinins
which chemical mediators induce fever?
1) Prostaglandins
2) Cytokines
What are the vasoactive amines?
- Histamine and serotonin (imp neurotransmitter and in the GIT)
- Present in preformed stores in cells
- Among the first mediators to be released
- Promotes smooth muscle contraction (can cause bronchospasm “we must use anti-histamine”)