Flashcards in IMI2: Cells of the innate immune system Deck (57)
What is the purpose of the complement system?
To enhances the ability of phagocytic cells and antibodies to remove microbes and damaged cells.
What are the three main roles of the complement system?
1. Tagging opsonised foreign surfaces
2. Lysing membranes of foreign pathogens/cells
3. Indicating presence of a foreign invader to the cellular immune system
The process by which bacteria are covered with substances that make them more visible to the immune system and more susceptible to phagocytosis (tagged)
What are the three stages of opsonisation?
• Pattern recognition trigger
• Protease cascade amplification/C3 convertase
• Inflammation, Phagocytosis and membrane attack
What components is the complement system made up of?
A group of serum proteins named C1-C9 and there are 3 pathways by which it acts
What are the pathways by which the complement system acts?
Explain the Lectin pathway (long)
The Lectin pathway is triggered by PAMPs. Lectins bind specifically to carbohydrate molecules on the surfaces of pathogens. Mannose-Binding Lectins (MBLs) and ficolins bound to the bacterial surface are opsonised by MBL-Associated Serine Proteases (MASPs). MASPs can cleave C4 into C4a and C4b. This promotes the cleavage of C2 into C2a and C2b. C2a and C4b combine to form C3 convertase.
What is the lectin pathway triggered by?
What proteins are bound to the bacterial surface that are opsonised by MBL-Associated Serine Proteases (MASPs) in the lectin pathway?
- Mannose-binding lectins (MBLs)
Describe the Classical pathway
The Classical pathway is activated by antibodies, and C1 (Recognition C1q and proteases C1s and C1r) binds to antibody-antigen complexes to activate it. Once active, C1 triggers the cleavage of C2 into C2a and C2b, and C4 into C4a and C4b. C2a and C4b combine to form C3 convertase.
What is the classical pathway activated by?
Explain the Alternative pathway
The Alternative pathway works by a different mechanism, as circulating C3 undergoes spontaneous cleavage into C3a and C3b. C3b reacts with Factor B, Factor D, and Properdin proteins to form the C3 convertase complex.
What does C3 cleave into spontaneously?
C3a and C3b
What does C3b react with? To form what?
What do all of the complement pathways have in common?
What do C3a and C5a promote?
What does C3b bound to the bacterial surface promote? When?
Phagocytosis when C3b receptors on phagocytes' surface bind to it.
How is the membrane attack Complex (MAC) formed?
When Properdin binds with C3 convertase, forming C5 convertase and C5 convertase cleaves C5 into C5a and C5b. C5b binds to C6, C7, C8 and C9, forming the MAC
What are anaphylatoxins made up of?
Discarded C3, C4 and C5 fragments
What do anaphylatoxins do?
They induce a local inflammatory response
What are C3a and C5a able to generate?
A chemotactic gradient, which promotes phagocytosis (recruit phagocytic cells to the site of infection)
How is anaphylactic shock triggered?
By systemic release of complement proteins
What does MAC do?
Completion of the membrane cascade leads to formation of MAC which disrupts the cell membrane causing cell-lysis
What are the three types of leukocytes in the body?
Name the three types of granulocytes and their % proportions
i. Basophils – 0.4%
ii. Eosinophils – 2.3%
iii. Neutrophils – 62%
Name the three types of Lymphocytes
i. T cells
ii. B cells
iii. NK cells
What percentage do monocytes make up?
What are the two types of monocytes?
Macrophages and Dendritic cells
What is the most common leukocyte?
Neutrophils (polymorphonuclear leukocytes)