Molecules of the Innate Immune System Flashcards
(48 cards)
Classes of innate immunity molecules
PRRs Fc receptors Cytokines Defensins Complement Acute phase proteins
What are examples of PRRs?
Toll-like receptors TLR-4, TLR-2 and TLR-3
Mannose receptors
What does TLR-4 do?
On most cells
Recognises Lipopolysaccharides on gram -ve bacteria
What does binding of LPS to TLR-4 result in?
Activation of the cell as binding triggers intracelllular cascades
What does TLR-4 recognise?
LPS on gram -ve bacteria
What does TLR-2 recognise?
Proteoglycans on gram +ve bacteria
Why are Toll-like receptors broadly specific?
Their targets are specific protein sequences, but these are present on many cells so they affect a large range of bacteria.
What does TLR-3 recognise?
Double stranded RNA
What is the difference between TLR-3 and TLR-4/2?
TLR-4/2 are found on CSM
TLR-3 are found intracellularly
What are mannose receptors?
Mannose are found on all cells, but usually they are blocked by other sugars
Bacteria, however have mannose as their surface sufar
Therefore, evolution has told hosts that cells with mannose as their surface sugars are non-self and should be destroyed
What constitutes the complement system?
Zymogens
How many molecules constitute the complement system?
20-30
How are zymogens activated?
By three mechanisms:
Classical - antigen-antibody interactions and C-reactive proteins
Alternative - structures on microbial cell wall
Lectin - receptors recognising sugars
Give an example of a lectin pathway-activating receptor
Mannose-binding lectin
What pathways are usually stimulated during infection?
Normally all the pathways are stimulated
What happens upon activation of the complement pathway?
C3 splits into C3a and C3b
C3b splits C5 into C5a and C5b
What is the role of the comlpement zymogens?
C3d is involved in activation of B cells
C3b and C4b opsonises molecules
C5a and C3a are acute inflammatory proteins that attract neutrophils out of the blood stream and into the tissue by releasing histamines that losen epithelium
C3a, C4a and C5a cause mast cell degranulation and enhanced permeability by the release of cytokines
C5b, C3b and C6/7/8 form MAC?
What is the role of C3d?
B cell regulation
What is the role of C3b and C4d?
Opsonisation.
Phagocytes contain membrane receptors that recognise complement and cause phagocytosis of opsonised molecules
What is the role of C5a and C3a?
Chemotactic molecules
Increase vascular permeability by the release of histamines so the neutrophils can travel from the blood to the tissues
What is the role of C4a, C3a and C5a?
Mast cell degranulation and enhanced permeability by release of cytokines
What complement zymogens form the MAC?
C5b, C3b, C7-9
What is the MAC?
Membrane attack complex
Forms a pore in the bacteria which dysregulates the electroc potential across the membrane and causes cell lysis.
What regulates the complement cascade?
T regulatory cells
