Innate immune system exam Flashcards
(118 cards)
1
Q
What is the first line of defense?
A
skin, mucous membranes, secretions of skin and mucous membranes
2
Q
What is the second line of defense?
A
innate immunity: phagocytic white blood cells, antimicrobial proteins, the inflammatory response
3
Q
What is the third line of defense?
A
Adaptive immunity: lymphocytes, antibodies
4
Q
What are the barriers that prevent pathogens from colonizing the lumina and subepithelial tissues?
A
skin, gut, lungs, eye/nose/oral cavity
5
Q
What is the mechanical barrier in the first line of defense?
A
epithelial cells joined by tight junctions
Skin/gut - longitudinal flow of air or fluid
Lungs - movement of mucus by cilia
E/N/O cavity - tears + nasal cilia
6
Q
What is the chemical barrier in the first line of defense?
A
Antimicrobial peptides: most epithelial cells continuously produce AMPs
Skin - fatty acids
Gut - low pH antimicrobial enzymes
Lungs - pulmonary surfactant
E/N/O cavity - antimicrobial enzymes in tears + saliva
7
Q
Example of a cell that produces AMPs
A
paneth cells in the crypt of the intestine produce alpha-defensins (which controls #no. of gut commensals + keep out pathogens)
8
Q
Innate immune response in 0-4 hours
A
infection > recognition by preformed non-specific / broadly specific effectors (AMP and complement proteins) > removal of infectious agent
9
Q
Early induced innate response (4-96 hours)
A
infection > recognition of microbial-associated molecular patterns (PRRs) > inflammation recruitment + activation of effector cells > removal of infectious agent
10
Q
Adaptive immune response ( >96 hours)
A
uses antigen specific receptors e.g t cells and b cells
11
Q
lymphoid organs
A
bone marrow, thymus
tonsils + adenoids, lymph nodes, appendix, spleen, Peyer’s patches, lymphatic vessels
12
Q
Name the innate immune cells + why we need do many different ones
A
Macrophage, dendritic cell, mast cell, natural killer cell, complement protein, granulocytes: neutrophil, basophil, eosinophil
because pathogens differ in size, mode of infection, and location of infection
13
Q
Modes of infection
A
airborne, waterborne or foodborne, (in)direct contact with feaces, blood-blood contact
13
Q
Locations of infection
A
luminal pathogens (outside) (any)
cytoplasmic pathogens (viruses)
endosomal pathogens (parasites/bacteria)
extracellular pathogens (bacteria/fungi)
14
Q
Infection mobilizes specialized innate immune cells for elimination of main classes of pathogens. Which pathogens mobilize which immune cells?
A
Viruses - Natural Killer cells
Macrophages - endosomal bacteria
Eosinophilic granulocytes - parasites
Neutrophilic granulocytes - extracellular bacteria/fungi
15
Q
When epithelial tissues become infected what happens?
A
PRRs on immune cells (e.g macrophages) recognize specific features on pathogens (PAMPs) > non-immune cells also have PRRs (e.g epithelial cells) + produce antimicrobial peptides (AMPs) > PRR activation > release of cytokines + chemokines which initiate inflammation by attracting effector cells (e.g NK cells + neutrophils) > complement activation > inflammation > vasodilation (due to cytokines) which increases permeability allowing immune cells to move from bloodstream to site of infection
16
Q
What else is necessary to eradicate infection besides this primary inflammation?
A
Not only innate immunity but also adaptive immunity, a second phase of inflammation is required which is mediated by T cells and B cell-derived antibodies
17
Q
principle characteristics of innate immunity vs adaptive immunity
A
rapid response (hours) vs slow (days to weeks)
fixed (PRRs) vs variable (B and T cell receptors)
limited specificity vs numerous highly selective specificities
constant during response vs improve during response
18
Q
consequences of dysfunctional immune system:
A
too little: immunodeficiency, cancer
too much: autoimmunity, allergy, autoinflammation
19
Q
What type of protective immunity responds to the different sites of infection?
A
Intracellular:
Cytoplasmic - NK cells, cytotoxic T cells
Vesicular - T cell + NK cell dependent macrophage activation
Extracellular:
Epithelial surfaces - AMPs + antibodies (especially IgA)
Interstitial spaces, blood, lymph - complement + phagocytosis + antibodies
19
Q
Name ILCs
A
NK cell, ILC1, ILC2, ILC3
19
Q
Name myeloid cells:
A
macrophages, neutrophils, dendritic cell, basophil, eosinophil
20
Q
Name adaptive cells
A
T and B cells
21
Q
What are the 2 types of PRRs
A
receptors for phagocytosis
receptors for inflammation
21
Types of PRRs for phagocytosis
glucan and mannose receptors recognise sugar structures on bacteria + fungi(only glucan)
complement receptors bind to complement-opsonized pathogens
scavenger receptors "scavenge" for pathogens but recognize many types of structures
22
What is complement
a system of plasma proteins that destroy pathogens
23
How do toll-like receptors work
Convex surfaces of TLR1 and TLR2 have binding sites for lipopeptide
Binding of each TLR to the SAME lipopeptide induces dimerization > triggers TIR domains to initiate signalling (> production of cytokines etc)
23
PRRs for inflammation PRR signalling pathways
toll-like receptor signaling, inflammasome, nucleic acid sensing
23
PRRs for inflammation are needed for…
needed for the production of AMPs, chemokines and cytokines
24
What does TLR2 recognize?
Gram positive bacteria (specifically the peptidoglycan (PGN) from the bacteria) (outside cell)
24
What does TLR4 recognize?
Gram negative bacteria (specifically the lipopolysaccherides (LPS) from the bacteria) (outside cell)
25
What does TLR4 activation lead to?
NFkB activation (type of transcription factor that activates a series of anti-bacteria/fungal AMP, cytokine and chemokine genes) (e.g IL-6, TNF-alpha)
26
What does TLR3 recognize?
double-stranded RNA from viruses
27
What happens when there is an abscence of functional NOD2
AMP production decreases > imbalance in gut microbiome > dysbiosis + inflammation
NOD2 preserves gut health
28
Which PRRs recognize bacteria
+ what happens when they recognize PAMPs
NOD1 and NOD2
Recognize a small fragment of bacteria peptidoglycan (PAMPs)
Once this PRR detects its ligand > activates NFkB > production of chemokines, cytokines, AMPs > inflammation + aids elimination of pathogen
Mutation in NOD2 = Crohns disease
29
Which PRRs detect viruses
RLRs (Rig-like receptors) = Cytosolic
TLR3 = Endosomal
These receptors lead to activation of IRF-3 which then activate Type I IFN
TLR3 also recruits adaptor protein TRIF which activates IRF-3 > activates/secretes Type I IFN
30
What do Type I IFN do?
Induce resistance to viral replication in all cells
Increase MHC class I expression + antigen presentation in all cells
Activate dendritic cells + macrophages
Activate/recruit NK cells to kill virus-infected cells
every cell can produce type I INF after direct infection w/ a virus
30
Characteristics of plasmacytoid dendritic cells
produce very high amounts of type I interferon = have a strongly
developed rough ER
31
How do TLRs signal for defense patterns (from cell surface)
Ligand binding + dimerization > recruits adaptor protein MyD88 > translocation of NFkB to nucleus > synthesis and secretion of cytokines (e.g TNF-alpha)
32
Chemokines e.gs
Antibacterial CXCL8 (Attracts neutrophils)
Antiviral CXCL10
33
Process of inflammasome pathway
NLRP3 kept in an inactive conformation
Stress signals activate NLRP3 = form an oligomer/complex with ASC > recruits and activates caspase 1 which then releases inflammatory cytokines e.g IL-1, IL-18
33
How does infection induce the migration of immune cells from the blood to tissues
bacteria trigger macrophages to release cytokines + chemokines
Vasodilation + increased vascular permeability = redness, heat, + swelling
Inflammatory cells migrate into tissue, releasing inflammatory mediators that cause pain
34
Which adhesion systems are simultaneously used by immune cells during migration from blood to tissue?
1) selective for different tissues (e.g mucosa vs skin)
selectin-mediated adhesion which allows immune cells to roll along the endothelium
2) very firm adhesion system, widely ysed by all immune cells (acts like velcro)
allow cells to "crawl" for diapedesis (cells squeeze through endothelial cell layer of blood vessels)
rolling adhesion (selectin/addressin), tight binding (CXCL8R/CXCL8), diapedesis (LFA-1/ICAM-1), migration
35
Macrophage
long-lived phagocytes present in healthy connective tissues + fight extracellular and endosomal pathogens
vaccum-cleaner of the body (degrade invading pathogens by phagocytosis)
antigen presentation
macrophage receptors recognize components of microbial surfaces, microorganisms are bound by phagocytic receptors on the macrophage surface, microorg. are internalized by endocytosis, fusion of endosome w/ lysosome = a phagolysosome in which microorg. are degraded
36
Neutrophils
short-lived phagocytes that fight extracellular pathogens
Phagocytic biological material is degraded in phagolysomes
Bacterium is phagocytosed by neutrophil, phagosome fuses w/ azurophilic and specific granules, antimicrobial response is activated, bacterium is killed and degraded, neutrophil dies by apoptosis + is phagocytosed by macrophage
37
summarize what activated neutrophils do
Activated neutrophils:
* Phagocytosis
* Degranulation
* Release mediators, cytokines
* Reactive oxygen species (ROS) production
* Release neutrophil extracellular traps (NETs) netosis
37
Effect of ROS production
Efficiency of intracellular killing can be temporarily enhanced
through the spiking of production of toxic reactive oxygen
species (H2O2 and O2-) within phagolysosomes
38
What is netosis
neutrophil spills out DNA and content of granules, creating a sort of fishing net over the bacteria
They contain DNA, histones, Elastase, Cathepsin G, Proteases
39
What happens if neutrophils dont work properly
CGD (chronic granulomatous disease)
40
Eosinophils
short-lived cells that fight nematodes
activated function: killing of anti-body coated parasites
No expression of FCeR
41
basophils
Short-lived cells that fight nematodes
actiavted function: augmentation of anti-parasitic response + promotion of allergic responses, produce heparin
high expression of FCeR
42
Mast cells
long-lived cells present in healthy
connective tissues and contribute to vasodilatation and fight nematodes
activated function: release of granules containing histamine and active agents
high expression of FCeR
43
Degranulation of mast cells
Preformed inflammatory mediators
* Histamine
* Proteases
* Serotonine
* Heparine
Newly synthesized mediators
* Prostaglandins
* Leukotrienes
* PAF
* Cytokines
* Chemokines
43
Name innate lymphocytes
+ characteristics of these
Group 1: NK cell, ILC 1
Group 2: ILC2
Group 3: ILC3, LTi cell
No antigen specific receptor, no receptor diversity, rapid response, no memory
44
Name adaptive lymphocytes
+ characteristics
B cell (BCR), T cell (TCR): CD4+ T cell and CD8+ T cell
Antigen specific receptors, High receptor diversity (i.e BCR and TCR i express on my cells are diff from those other people's cells express), slow response, has memory cells
45
Which lymphocytes have cytotoxic activity?
+ what percentage of blood lymphocytes do these make up?
Innate: Cytotoxic ILC NK cell (5-25%)
Adaptive: Cytotoxic CD8+ T cell (5-30%)
46
Which lymphocytes have cytokine activity?
+ what percentage of blood lymphocytes do these make up?
Innate: Helper ILC (0.1%, mostly tissue resident)
Adaptive: CD4+ T cell (25-60%)
Produce cytokines + respond to cytokines in surrounding env.
47
Compare the cytotoxic lymphocytes
NK cell:
no antigen specific receptors
activated by cytokines or stress induced
CD8+ T cell:
TCR (antigen specific receptor)
Activated by MHC-I antigen presentation
48
Which pathogens do the innate lymphocytes fight? (+ function of LTi cells)
Group 1: viruses and intracellular bacteria and tumor cells
Group 2: helminths and protozoa
Group 3: ILC3 bacteria + fungi
(Lti cell lymph node formation, they are important during early embryonic dev.)
48
Compare the cytokine lymphocytes
Helper ILC:
No antigen specific receptor
Activated by cytokines + lipids
CD4+ T cell:
TCR
Activated by MHC-II antigen presentation
49
briefly how do ILCs function?
ILC1: Produce cytokines = help macrophages clear viral infections
ILC2: help eosinophils be more effective + produce greater numbers of eosinophils
ILC3: recruit neutrophils from bloodstream
50
How do NK cells identify pathoigens and how are NK cells activated?
Identification + activation:
If a virus infuses its genetic material into a cell PRRs in the cytoplasm (cytosolic PRRs) sense that genetic material of a foreign nature has entered > Type I interferon production > interferon response: (induce resistance to viral replication in all cells, increase expression of ligands for receptors on NK cells, activate NK cells to kill virus-infected cells)
51
Why do NK cells not kill any cell?
They have activating and inhibiting receptors
Healthy cells: MHC I molecules on all nucleated cells will bind to the inhibitory receptor on the NK cell
Tumor cell or virus infected cell has an activating ligand that binds to the activating receptor on the NK cell (e.g MIC expression)
52
How do NK cells kill virally infected cells?
Once NK cell identifies a target cell is infected with a virus (or tumor cell):
Direct killing: NK cell makes contact w/ target cell (synapse formed with membranes) + contents of cytoplasmic granules (containing cytotoxic molecules: perforin and granzyme) is released into the target cell > granzymes diffuse into cell and cause apoptosis
Indirect killing: Type II Interferon (IFN gamma) production by NK cells > activate macrophages > increased phagocytic activity, upregulation MHCI/II, production of IL-12/IL-15
53
Consequences of NK cell deficiency or insufficiency?
mostly suffer from herpes virus infections
Reduced circulating NK cell levels and function correlates with severity of Sars-CoV2 infection in COVID-19 patients
54
How does ILC1 fight pathogens
Inducing cytokine (from DC, macrophages or epithelial cells in tissues) > ILC activated > effector cytokines (produced by ILC) > target pathogen
IL-12 > ILC1 > IFN-γ, TNF-α > macrophage activation > viruses + intracellular bacteria
55
How does ILC3 fight pathogens
IL-1beta, IL-23 > ILC3 > IL-17, IL-22 > phagocytosis, AMPs > bacteria + fungi
55
How does ILC2 fight pathogens
IL-25, IL-33, TSLP > ILC2 > IL-4,IL-5, IL-13 > mucus production, macrophage activation, vasodilation > helminths + protozoa
56
Adverse effects of ILC3
Chronic inflammation in lung: asthma
Chronic inflammation in skin: Psoriasis
Promote tumor growth and tissue inflammation
57
Role of IL-22
Regulating tissue repair in the intestine
- stem cell regeneration
- mucus production
57
sites of microbe entry
skin, GI tract, respiratory tract, human blood vessel
58
Capture of antigen + presentation (brief structure)
site of microbe entry > immune cells capture antigens using PRRs > present them to sites of T cell activation
e.g specialized DC at epithelial barriers capture antigens + bring them to lymph nodes
58
sites of T-cell activation
lymph nodes, spleen, mucosal and
cutaneous lymphoid tissues
59
How do T cells distinguish antigens from different pathogens?
T-cell receptors recognize peptide antigens bound to MHC molecules (on Dendritic cells)
59
Antigen uptake, processing, presentation
Uptake: DC takes up pathogen for degradation
Processing: Pathogen is taken apart inside the DC
Pathogen proteins are cut into small pieces
Presentation: Peptides bind to MHC molecules + the complexes go to the cell surface
MHC:antigen complex is recognized by TCR (antigens recognized are short peptides)
60
MHC molecules structure during infection vs no infection
only exist on the cell surface when it forms a unit with a peptide
Absence of infection: MHC molecules will only carry self peptides (not to worry bc: T cells with TCRs recognizing a MHC-selfpeptide complex are deleted during their development in the thymus in the process of negative selection)
60
Structure of MHC class I vs MHC class II
Have different polypeptide chains
MHC class I: 1 transmembrane heavy chain (or α) + a nonconvalentely bonded β2-microglobulin
MHC class II: 2 transmembrane chains (α chain and β chain)
61
Which type of T cell does each MHC molecule present peptide antigens to?
MHC class I presents peptide antigens to CD8+ cytotoxic T cell
MHC class II presents peptide antigens to CD4+ Helper T Cell
62
How do cytotoxic T cells work?
MHC:antigen complex presented to CD8 cell, alters the cell > killing it
63
How do Helper T cells work?
CD4 T cell interacts w/ macrophage > Improve capacity of macrophages to
phagocytose extracellular pathogens and secrete cytokines
or
CD4 T cell interacts w/ B cell > Help B cells to make high affinity antibodies that bind extracellular bacteria/virus to ensure their elimination
64
CD4 and CD8 are T-cell co-receptors
cooperate w/ TCR in the
recognition of peptide:MHC complexes,
= activation of selected genes
bind to sites in MHC class I and MHC class II BUT not the same site that TCR binds to
65
Summary of molecular mechanisms of antigen processing
Intracellular antigen > antigen processing to peptides in cytosol via proteasome > peptides transported to ER > peptide binding by MHC I > MHC I presents peptide at cell surface
Extracellular pathogen/antigen > degraded in phagolysosomes (acidic endocytic vesicles) > peptides produced > peptides bind to MHC II > MHC II presents peptide at cell surface
66
Zoom into the peptide:MHC class I complex binding process + how it leaves the ER
Peptide is delivered by TAP to the class I heavy chain = conformational change that breaks the peptide hold of tapasin to the peptide **= allows MHC:Peptide complex to leave the ER in a membrane-enclosed vesicle
** + peptide editing: peptides are trimmed by ERAP to stably fit MHC-I molecule
67
Role of immunoproteasomes
anti-viral cytokines (e.g IFN) proteasomes become more effective immunoproteasomes
1. Various subunits are replaced for the production of peptides with carboxyterminal residues that
improve MHC class I binding
2. Addition of proteasome activator PA28 speeds the release of peptides from proteosome
68
Zoom into the peptide:MHC class II complex binding process + how it leaves the ER
Invariant chain temporarily blocks peptide binding until “MHC class
II’ vesicles fuse with phagolysosomes
Fusion of phagolysosome (acidic low PH activates proteases = peptides) with MHC II vesicles
69
Peptide binding groove of MHC I
The two ends of the peptide
are pinned down into the
pockets at each end of the
groove
Peptides that bind MHC class I
molecules are 8-10 amino acids
in length
70
Peptide binding groove of MHC II
the two ends of the peptide extend out from each end of the groove
Peptides that bind MHC class I
molecules are usually 13-25
amino acids long
71
What is cross-presentation
Antigen-derived peptides from phagolysosomes are also presented on MHC class I molecules
dying virus-infected cells are ingested >
DCs can leak peptides from phagolysomes into the cytosol
> DCs will present virus-derived
peptides on MHC class I molecules
72
Which cells express MHC I and MHC II
All nucleated cells (so, not erythrocytes) express MHC class I
MHC class II: B cells, T cells, Dendritic cells, Thymic epithelium cells
73
Peptide/MHC limitations
The ability of MHC molecules to bind a peptide is strongly limited
The groove can bind only limited #no. of peptides types
74
What increases the number of peptides that can bind to the MHC molecule?
- Promiscuity (the binding of look-a-like peptide types to a single MHC)
- MHC isotypes (a result of multiple genes: HLA-A/B/C/DR/DP/DQ)
- MHC allotypes (a result of polymorphisms: HLA-A1001/A1002 etc)
75
Expand on promiscuity in MHC binding
anchor amino acids in MHC groove may differ in characteristics and they bind to peptide antigens with matching characteristics
76
Expand on MHC allotypes
MHC I variability: Allotypes arise by point mutations (polymorphisms) and interallelic (gene conversion).
MHC II variability: MHC allelic variation within peptide binding pocket and TCR contact residues.
Different HLA alleles bind different pathogen-derived peptides,
which increases the diversity in antigen presentation
76
Expand on MHC isotypes
Human cells express MHC gene isoforms:
* Three different class I molecules
(HLA-A, HLA-B and HLA-C)
* Three different class II molecules
(HLA-DP, HLA-DQ and HLA-DR)
77
MHC restriction
TCRs are very precise
A given TCR that recognizes a certain
MHC/peptide combination will not be able to recognize another peptide
(Y) in the context of the same MHC molecule.
There will be another TCR
to recognize this particular
peptide/MHC combination
78
Brief overview of complement system:
Complement proteins circulate in the blood inactive
Cascade of enzymatic reactions: each
component activates the next component
The cleaved products are biologically active (cleaved protein produces A:small fragment + B:large fragment)
79
What does the complement system revolve around
C3 and cleaving C3
80
What are the efffector functions of the complement system?
Lysis - direct killing of the bacteria (the terminal pathway)
Opsonization - flagging it for the immune system (marks any surface for phagocytosis)
Signaling - signaling to immune cells and tissues that there is an infection going on (C5a and C3a)
80
What are the activation pathways of the complement system?
3 ways to get to C3
Classical
Alternative
Lectin
81
Activation of C3
Cleavage of C3 to C3a + C3b (exposes thioester bond which reacts w nucleophiles on pathogens) > C3b covalently binds to pathogen
C3b also forms new AP convertases
82
What are the 2 types of C3 convertase?
Alternative pathway: C3bBb
Classical/Lectin pathway: C4b2a
83
Pattern recognition molecules on the classical and lectin pathway:
+ the proteases they carry
C1q for classical (C1r + C1s)
MBL, ficolin, collectin for lectin (MASP-1 + MASP-2)
84
Proteases are activated upon binding explain this in relation to C1q
C1 binds to C-reactive protein on pathogen surface > activates classical pathway > cleaves C4
85
Proteases are activated upon binding explain this in relation to MASP
Activated MASP-2 cleaves C4 and also C2 > C4b binds to microbial surfaces + C2a binds to surface of C4b = forms classical C3 convertase C4b2a > C4b2a binds C3 + cleaves it to C3a + C3b > feedback loop
86
How does the alternative pathway synthesize C3?
Via autoactivation: C3 is a little bit unstable, it can autoactivate (fluid phase) (has to occur very close to the pathogen surface) if this happens you go to the second part of the alternative pathway
Surface amplification: starts w/ C3b (can come from wherever) > generates C3 convertase C3bBb > generates more C3
87
Effect of high density of C3b deposition (Lysis)
Lysis
Changes C3 convertase into C5 convertase > C5a + C5b > terminal pathway leads to membrane attack complex (MAC) (C5b-9) > lysis
88
Effect of MAC on bacteria
generates a massive pore (generates many holes in the membrane) = influx of calcium into the cells which is toxic = lysis
Gram - bacteria are very sensitive to MAC
Gram + have very large outer layer so MAC gets stuck in the layer and doesnt cause lysis
89
Effect of high density of C3b deposition (Opsonisation)
complement activation = Cb3 deposition on cell surface > CR1 on macrophage binds C3b on bacterium > endocytosis of the bacterium by the macrophage > phagosome > phagolysosome
90
Signalling in the complement system
- Two anaphylatoxins are generated during complement activation
- C3a and C5a (chemoattractants to immune cells)
- Each acts on receptors (C3aR, C5aR1, C5aR2) expressed on a wide range of cells
e.g act on blood vessels to increase vascular permeability > extravasation of complement to site of infection > migration of neutrophils + monocytes to tissues is increased
91
Characteristics of the complement system:
is a cascade
powerfull
induces damage
a-specific
92
How is the complement system regulated
Further cleavage inactivates fragments
Convertases are tightly regulated
Surface bound regulators
Fluid phase regulators
93
How is C3b tightly controlled to prevent damage to their own tissues during complement activation?
controlled by host cells: regulatory proteins on host cell surfaces either dissociate the C3 convertase or inactivate C3b (preventing the complement system from damaging self-cells)
CD55 (Decay Accelerating Factor): Dissociates the C3 convertase (C3bBb).
CD46 (Membrane Co-factor Protein) and CD35 (Complement Receptor 1): Both work with Factor I to inactivate C3b and prevent complement amplification on host cells
94
What inhibits MAC formation
CD59
95
What is the most important regulator of the AP ?
Factor H
96
Characteristics of Factor H
- Abundant fluid phase protein
* Competes with Factor B
* Accelerates C3bBb decay
* Is a cofactor for Factor I to inactivate C3b
* Acts in fluid phase and on host surfaces
97
What happens when there is insufficient activation and excessive regulation of the complement system
cancer + infections e.g Meningococcal disease
98
What happens when there is excessive activation and insufficient regulation of the complement system
autoimmune disease (Auto-antibodies directed against own cells), kidney diseases (they become vulnerable), hematological diseases
99
Complement therapeutics:
eculizumab
Inhibits C5 cleavage into C5a and C5b
= less neutrophil influx + inflammation + no MAC bc no C5b
