10.2 The Innate Immune System Flashcards
What types of barriers exist within the static barrier of the innate immune system?
- Mechanical
- Chemical
- Microbiological
Is the epidermis permeable to bacteria?
No
How does sebum play a role in killing bacteria?
- Changes pH down to about 3-5 due to lactic and fatty acid release
- Denatures enzymes in bacteria -> death
Where can mucous membranes be found?
- Respiratory tract
- Gastrointestinal tract
- Urogenital tract
What does mucous contain?
- Mucin (glycoprotein)
- Anti-microbial proteins
- Inorganic salts
When commensal microbes digest dietary fibres, what do they produce?
- Metabolites
- Vitamins
- SCFAs
How do commensal microbes fight with pathogenic microbes?
- Lactic acid produced by lactobacilli (too acidic for some pathogens)
- Bacteriocin production (antimicrobial peptides)
How can commensal microbes cause disease?
- Called “opportunistic pathogens”
- Take over in situations where the immune system is distracted by weakness/stress of some kind
General mode of action of AMPs (+Charge)
- Cationic proteins
- Disrupt membrane integrity/cell anabolism
Where are AMPs produced?
- Keratinocytes
- Mucosa
- Neutrophils
- Macrophages
Why do AMPs preferentially disrupt bacterial membranes over mammalian membranes?
- Bacterial membranes have negative charge, whereas mammalian cells do not
- AMPs are positive (therefore attracted)
What are the three pathways by which the complement system can be activated?
- Classical pathway
- Alternative pathway
- Lectin pathway
Describe the classical pathway of complement activation
C’ recognising antibody:antigen complex
Describe the alternative pathway of complement activation
C’ binding generally to microbe surface
Describe the lectin pathway of complement activation
C’ binding to sugar residues on bacteria surface
What are the three outcomes following complement activation?
- Opsonisation
- Initiation of inflammatory response
- Punching holes in cell membranes
What complex punches holes in cell membranes following complement activation?
Membrane Attack Complex (MAC)
What is released to trigger the inflammatory response following complement activation? What does this also do?
- Anaphylotoxins are released
- Chemoattractants to phagocytes
Describe opsonisation following complement activation. Which proteins are used?
Coats microbe surface with C3b proteins to promote phagocytosis
When can a monocyte differentiate to become a macrophage?
When migrating from blood to tissue
Which immune cell is the number one defence against prokaryotes?
Neutrophils
What cells do NKCs target?
- Tumour cells
- Cells affected by virus
- Cells affected by intracellular bacteria
Which cells take care of intracellular/extracellular bacteria?
Intracellular: NKCs
Extracullular: Neutrophils and macrophages
Phagocytosis vs endocytosis
Phagocytosis: Whole organisms and other cells
Endocytosis: Macromolecules
What are the two mechanisms of endocytosis other than phagocytosis?
- Pinocytosis (invagination to form vesicles, vesicles form endosome, digested by lysosomes)
- Receptor-mediated endocytosis (bind to receptor, form vesicles, vesicles form endosome, endosome digested by lysosome)
Endocytosis vs phagocytosis: what do the vesicles form when combined?
Endocytosis: endosome
Phagocytosis: phagosome
What soluble proteins are used to tag microbes to make them more “palatable” for phagocytes?
Opsonins
How do opsonins make microbes more palatable?
- Bind to substance
- Phagocytes have receptor for opsonin -> phagocytoses
What receptors facilitate direct microbe recognition that triggers phagocytosis?
- Pattern recognition receptors (PRRs)
Which patterns do PRRs detect in gram negative/positive bacteria?
Gram-positive: Lipoteichoic Acid
Gram-negative: Lipopolysaccharide
What kinds of receptors are used during indirect microbe recognition that triggers phagocytosis?
Opsonin receptors
What are the two kinds of opsonin receptors, and what do they bind to?
FcR: Butt end of antibodies
C3bR (Complement protein C3b)
How do NKCs recognise tumour/infected cells?
They recognise that something is not right
