(L20) Innate Immunity Flashcards
What are some of the major barriers created by the innate immunity?
L20 S3-5
- skin
- acidic pH
- mucous epithelium
- ciliated epithelium
What are the hallmark characteristics of inflammation (5)?
L20 S8
- heat
- redness
- swelling
- pain
- loss of function
Why does the body induce inflammation during an infection?
L20 S11
Bloody supply to a region is increased during inflammation, aiding in bringing immune cells to the site. (Redness and warmth)
Vessels become more permeable allowing immune cells and immune plasma proteins to enter the site. (Swelling)
What causes fever?
Is it helpful or harmful to the host?
L20 S12
Fever is induced by the host immune system, not the pathogen!!!
Pyrogenic cytokines (TNF, IL-1, and IL-6) are responsible.
The body does this as pathogens replicate less effectively outside of normal physiologic body temperature.
How do innate immune cells differentiate between self and non-self?
L20 S14
PAMPs (pathogen-associated molecular patterns)
They are factors that are unique to pathogens and not found on host cells.
Typically they are common, constitutively express cell surface molecules that are required for the pathogens
What are examples of PAMPs?
L20 S15
- porin
- certain lipoproteins*
- certain lipopolysaccharides*
- lipoteichoic acid*
- teichoic acid
- mannoprotein*
- β-glycine
- lipoarabinomannan
What are TLRs?
What TLRs are extracellular and which are intracellular and what do they detect?
L20 S17-18
Toll-like receptor, form of PRR (pattern recognition receptor) that detects PAMPs.
Extracellular: (bacterial cell membrane components)
- TLR-1:2 (lipopeptides & GPI (parasites))
- TLR-2:6 (lipoteichoic acid (gram+) and zymosan (fungi))
- TLR-4:4 (LPS (gram-)
- TLR-5 (flagellin)
Intracellular: (bacterial DNA/RNA products)
- TLR-3 (dsRNA
- TLR-7 (ssRNA)
- TLR-8 (ssRNA)
- TLR-9 (CpG DNA)
What signaling pathways do TLRs activate and which TLRs activate each?
L20 S22
MyD88:
- all TLR except TLR3
- TLR4 activates both
TRIF:
- only TLR3 and TLR4
- TLR4 activates both
MyD88 and TRIF are adaptor protein which activate transcription factors NFκB and IRF
What are the results of MyD88 and IRAK-4 deficiencies?
L20 S27
Susceptibility to bacterial and viral infections.
What are NLRs and what is their function?
L20 S28-29
NOD-like receptors
Detect intracellular PAMPs and activate inflammasomes.
Inflammasomes activate caspase-1 which activates precursors of IL-1β and IL-18, pro-inflammatory
What are DAMPs and how are they different from DAMPs?
What are examples?
L20 S32
Damage-associated molecular patterns
Molecules that are released from damaged/dying host cells and activate PRRs on innate immune cells inducing inflammatory response.
Examples (all normally located in the cell hidden from immune cells):
- phosphotidylserine
- HMGB1
- uric acid
- HSP
What autoimmune disease are related to DAMPs?
L20 S37
- MS
- DM
- SLE
- RA
What is fMet and how is it used by the innate immune system?
L20 S40
Constituent of prokaryotes (PAMP) which is recognized by formal peptide receptor.
Used as a chemotatic factor by phagocytes
What are the functions of macrophages?
L20 S41
Detect PAMPs and DAMPs
Mediate extravasation/chemotaxis of other immune cells (inflammation)
Phagocytosis and tissue repair
Release of effector substances (cyto/chemokines, ROS, NO, prostaglandins, and defensins)
Ag presentation to T cells (APC)
Immunomodulation of other immune cells via cytokines
What are the functions of mast cells?
L20 S43-44
Mast cells can be proinflammtory or anti-inflammatory.
Primarily control blood vessel permeability (granule histamine), controlling extravasation of other immune cells.
Frequently primary and rapid response to innate immune triggers in tissues.
Differentiate between cytokines and chemokines.
What is the function of each?
L20 S50
Cytokines:
- long range signaling peptides
- extremely wide range of functions with frequent redundancies
Chemokines:
-chemoattractants that guide immune cells to areas of inflammation
What are the main categories of innate immune cytokines and what are the key examples of each?
L20 S51-52
Pro-inflammatory:
- TNF
- IL-1
- IL-6
- all the ones above induce FEVER
Anti-inflammatory:
- TGF-β
- IL-10
What is the most important regulator of macrophage function and where does it come form?
L20 S51
IFN-γ which is secreted by T cells
What is the major attractant of neutrophils?
L20 S52
IL-8
What are the different pathways of compliment activation and what is activating factor of each pathway?
L20 S55
Classical pathway:
-Ab binds pathogen and C1 recognizes Ab activating C2 and C4
Lectin pathway:
-MBL binds pathogen mannose and MBL activates C2 and C4
Alternative pathway:
C3 spontaneously degrades and C3b binds pathogen
What are the effector mechanisms of complement?
L20 S54
MAC (membrane attack complex) leading to cell lysis
Opsonization with C3b leading to phagocytosis
Production of anaphylatoxins (C3a, C4a, C5a) leading to vasodilation and degranulation
Clearance of Ab immune complexes
Enhancement of immune response (C3d binding CR2 of B cells)
What is the first step of complement cascade and what does this look like in each pathway?
L20 S56
Classical and lectin:
-C1 (classical) or MBL (lectin) convert C2 and C4 into C2a and C4b which binds pathogen and form C3 convertase (C4bC2a)
Alternative:
-C3 spontaneously cleaves (tickover) into C3b which bind pathogen. C3b converts factor B into Bb forming alternative C3 convertase (C3bBb)
What is the second step of complement cascade and what does this look like in each pathway?
L20 S57
Classical and lectin:
-C3 convertase (C4bC2a) converts C3 into C3b. C3b binds C3 convertase forming C5 convertase (C4BC2aC3B)
Alternative:
-alternative C3 convertase (C3bBb) converts C3 to C3b. C3b binds C3 convertase forming C5 convertase (C3bBbC3b)
What is the final step of complement cascade and what does this look like in each pathway?
L20 S58
Shared by all pathways:
- C5 convertase converts C5 to C5b
- C5b inserts into membrane
- C5b mediates insertion of C6, C7, and C8 into memabrane
- C5-8 insert numerous C9 forming a pore in membrane called the MAC (membrane attack complex)
What are APPs?
What are the most common examples?
L20 S60-61
Acute phase proteins
Elevated levels indicate inflammation (they molecules themselves don’t necessarily directly induce inflammation)
Examples:
- CRP (C-reactive protein)
- MBL/MBP (mannose binding lectin/protein)
- SAA (serum amyloid A)
What are the steps of neutrophil recruitment?
L20 S65-67
Tethering (rolling):
- activated endothelium expressed P and E selectin which bind their constitutively expressed ligands on neutrophils
- neutrophils stop
Tight binding:
- selectin bind stimulates expression of integrins (LFA-1 and VLA-4) on neutrophils which bind ligands on endothelium (ICAM-1 and VCAM-1)
- neutrophils stop
Diapedesis:
-neutrophils transmigrate across endothelium
Chemotaxis:
-IL-8 gradient directs neutrophil to site of inflammation
How does monocyte recruitment differ from neutrophil recruitment?
L20 S70
Tethering, tight binding, and diapedesis are the same
Chemotaxis is instead mediated by MCP-1 (monocyte chemoattractant protein-1)
Monocytes mature into Mφ once in tissue
What are the different pathways of Mφ activation and what is the function of Mφs of each pathway?
L20 S71
Classically activated (M1):
- activated by TLR and IFN-γ
- microbical effectors (phagocytosis, ROS, and NO)
- pro-inflammatory response (IL-1, IL-12, IL-23, and chemokines)
Alternatively activated (M2):
- activated by IL-13 and IL-4
- tissue repair and fibrosis
- anti-inflammatory (IL-10 and TGF-β)
How are pathogens recognized for phagocytosis and how are they killed once phagocytosed?
L20 S73-75
PRRs bind PAMPs stimulating phagocytosis forming phagosome
Phagosome fuses with lysosome forming phagolysosome
Bacteria killed via exposure to ROS and NO of lysosome (hydrogen peroxide,hydroxyl radicals, and hypochlorite)
How are viral cells recognized and killed?
L20 S77-80
Viral infected cells produce type I interferons (IFN-α/β)
IFN-α/β:
- blocks viral RNA translation (blocks GDP -> GTP)
- degrades viral RNA (ribonuclease L)
- activates NK cells
NK cells:
- kill virus infected cells releasing viruses
- produce type II interferon (IFN-γ) which stimulates phagocytes to uptake and destroy released viruses
How is NK activity regulated?
L20 S81-82
Activation:
- KAR (killer activating receptors) bind MICA and MICB which are expressed on stressed host cells
- KAR activate PTKs which generate activating signal
Inhibiting:
- KIR (killer cell IG like receptors) recognize constitutive class I MHC of healthy cells
- KIR activates PTPs which generate inhibitory signals
- class I MHC expression is inhibited in unhealthy cells
What is the mechanism of NK mediated cell killing?
L20 S83
NK cells release perforins which form pores in target cell
Granzymes are released next which enter targeted cell via pores and induces apoptosis
How does the innate immune system link to the adaptive immune system?
L20 S86-87
Innate APCs (antigen presenting cells) present processed antigens to lymphocytes stimulating development and maturation.
Innate cells also release cytokines that guide lymphocyte development and maturation.
