Innate Immune Responses !!!

Question 1

What is the main difference between innate and adaptive immunity?

Answer 1

The time they are activated!

Innate immunity is activated within 0-12 hours of infection, while adaptive immunity is activated within days.

Also, innate immunity doesn’t generate memory response.

Question 2

Which one of the statements is true regarding innate immunity?

1. Innate immunity are immediate and require prior exposure to the microbe.
2. There is no difference in the quality or magnitude of the innate immune response to a microbe upon repeated exposure.
3. Innate immunity is activated by the recognition of a large set of molecular structures that are either products of the microbes or are expressed by injured or dead host cells.

Answer 2

2!

1. Innate immunity are immediate and DO NOT require prior exposure to the microbe.
2. Innate immunity is activated by the recognition of a LIMITED set of molecular structures that are either products of the microbes or are expressed by injured or dead host cells.

Question 3

What are the three essential functions served by innate immunity?

Answer 3

1. Is the initial response to microbes & it prevents, controls, or eliminates infection of the host
2. Eliminates damaged cells and initiates the process of tissue repair
3. Stimulates adaptive immune responses and can influence the nature of the adaptive responses to make them optimally effective against different types of microbes

Question 4

(T/F) Without innate immunity, there is no adaptive immunity.

Answer 4

True!

Question 5

Epithelial cell barriers, secreted mucus, and antimicrobial substances are covered by immediate _______ immunity.

The response to an infection occurs in ______ phases.

Answer 5

Innate

Three (immediate innate, early induced innate, adaptive)

Question 6

What are the three functions of epithelia in immediate innate immunity?

Answer 6

1. Physical barrier to infection
2. Killing of microbes by locally produced antibiotics (defensins, cathelicidins).
3. Killing of microbes and infected cells by INTRAepithelial lymphocytes.

Question 7

1) While innate immunity has ________ ________ receptors, adaptive immunity has _________ _________ molecules.

2) Innate immunity receptors have _______ diversity compared to adaptive immunity.

3) Distribution of receptors in innate immunity is ________, while it is _________ in adaptive.

Answer 7

1) Identical mannose; distinct antibody

2) limited (encoded in germline as opposed to being encoded in genes)

3) NONCLONAL (identical receptors on all cells of the same lineage); CLONAL (clones of lymphocytes with distinct specificities express different receptors)

Question 8

Is there discrimination of normal cells and nonself in both types of immunity?

Answer 8

Yes!

Innate: healthy host cells are not recognized or they may express molecules that prevent responses.

Adaptive: based on selection against self-reactive lymphocytes - may be imperfect

Question 9

Immune cells tolerate self and recognize and kill non-self.

If there is a problem with tolerating self, it is called ___________ disease.

If there is a problem to recognize and kill non-self, it is called ___________.

Answer 9

Auto-immune

Immunodeficiency

Question 10

What are the three important roles served by MACROPHAGES in innate immunity? How do they do that?

Answer 10

1. Ingest and destroy microbes
2. Clear dead tissues or initiate tissue repair.
3. Produce cytokines that initiate inflammation.

The phagocytic functions of macrophages are mediated by CELL-SURFACE RECEPTORS, such as MANNOSE or SCAVENGER receptors, which directly bind microbes or dead cells.

They also recognize microbes and products of damaged cells using PRRs such as TLRs (toll) and NLRs (nod).

Question 11

What are PAMPs and DAMPs?

Answer 11

Pathogen-Associated Molecular Patterns; conserved small molecular motifs of microbes (LPS, flagellin, lipoteichoic acid, peptidoglycan, dsRNA, unmethylated DNA)

Damage-Associated Molecular Patterns; endogenous molecules produced by damaged or dying cells

Question 12

What are the three cellular locations of PRRs?

Answer 12

1. Extracellular membrane (TLR, C-type lectin R)
2. Cytosolic (nod/rig-like R)
3. Endosomal membrane (TLR)

Question 13

Toll-like receptor has a cytoplasmic domain homologous to the mammalian _____ receptor.

Answer 13

IL-1 (cytokine)

Question 14

(T/F) Without toll-like receptors, there was uncontrolled fungal growth in fruit flies.

Answer 14

True!

Toll signalling activates the synthesis of an antifungal peptide in flies.

Question 15

How many toll-like receptors do humans have compared to mice?

Answer 15

10 in humans

12 in mice

Question 16

Match the following PAMPs to their description:

1) LPS
2) Bacterial flagellins
3) Unmethylated DNA
4) ssRNA/dsRNA

A) structural proteins that form the major portion of flagellar filaments. flagella contribute to the virulence of bacteria through chemotaxis and invasion of host surfaces. they have a conserved domain widespread in pathogenic bacterial species.

B) produced as a replicative intermediate during virus life cycle.

C) a cell wall component of gram (-) bacteria.

D) methylation on the cytosine of CpG motif is critical in gene regulation in mammals, but not in pathogens. helps discriminate between the two DNA.

Answer 16

LPS: a cell wall component of gram (-) bacteria.

Bacterial flagellins: structural proteins that form the major portion of flagellar filaments. flagella contribute to the virulence of bacteria through chemotaxis and invasion of host surfaces. they have a conserved domain widespread in pathogenic bacterial species.

Unmethylated DNA: methylation on the cytosine of CpG motif is critical in gene regulation in mammals, but not in pathogens. helps discriminate between the two DNA.

ssRNA/dsRNA: produced as a replicative intermediate during virus life cycle.

Question 17

Match the following PAMPs to the TLRs that recognize them:

1) LPS
2) Bacterial flagellins
3) Unmethylated DNA
4) dsRNA
5) ssRNA
6) Bacterial lipopeptides
7) Bacterial peptidoglycan

A) TLR 1/2
B) TLR 3
C) TLR 4
D) TLR 5
E) TLR 6
F) TLR 7/8
G) TLR 9

Answer 17

LPS: lipid A portion is recognized by TLR 4

Bacterial flagellins: TLR 5

Unmethylated DNA: TLR 9

dsRNA: TLR 3

ssRNA: TLR 7/8

Bacterial lipopeptides: TLR1/2

Bacterial peptidoglycan: TLR 6

Question 18

TLR 1, 2, 4, and 6 _____ surface expression facilitates the recognition of _________ components. They are highly expressed on the surface of ___________ and _______.

TLR 3, 7/8, 9 expression inside ________ facilitates the recognition of ________ nucleic acids and decrease the risk of contact with host DNA. TLR 7, 9 are highly expressed inside of _________ ____.

TLR 5 is expressed in _________ tissues and expressed on _________ and _________ cells.

Answer 18

cell; bacterial; neutrophils and macrophages (professional phagocytes + produce pro-inflammatory CYTOKINES)

endosomes; viral; plasmacytoid DC (profession INTERFERON producing cells)

mucosal; intestinal epithelial and dendritic cells.

Question 19

What are the two major domains of the TLRs? Briefly describe their functions.

Answer 19

1) Leucine rich region (LRR) domain: responsible for MOLECULAR RECOGNITION.

2) Toll/interleukin-1 receptor domain: required for the INTERACTION with TIR-containing ADAPTOR PROTEINS (MyD88, MAL, TRIF, and TRAM), which trigger downstream signaling pathways.

Question 20

Match the two major domains of TLRs to their description:

1) Leucine-rich region domain

2) Toll/interleukin-1 receptor domain

A) the name comes from the fact that the receptor for the cytokine interleukin 1B has. TIR domain in its cytoplasmic tail.

B) includes the highly conserved segment, LxxLxLxxNxL, in which L is hydropobic residues. Generates a HORSE SHOE-shaped structure.

Answer 20

Leucine-rich region domain: includes the highly conserved segment, LxxLxLxxNxL, in which L is hydropobic residues. Generates a HORSE SHOE-shaped structure.

Toll/interleukin-1 receptor (TIR) domain: the name comes from the fact that the receptor for the cytokine interleukin 1B has. TIR domain in its cytoplasmic tail.

Question 21

What happens when TLR-2 and TLR-1 bind to the lipid side chains of triacyl lipopeptides?

Answer 21

Binding of each TLR to the same lipopeptide induces DIMERIZATION, bringing their cytoplasmic TIR domains into close proximity.

*similar to cytokine binding

Question 22

(T/F) Mammalian TLRs make direct contact with PAMPs.

Answer 22

True!

All TLRs have a horse shoe-shaped motif for recognition but how they recognize their ligand is different.

Question 23

Answer the following questions regarding TLR signalling:

1) What does it induce?

2) What does ligand binding do?

3) Which four adaptor proteins does it depend on? What do they do?

4) What two main signalling pathways does it activate?

Answer 23

1) Induces the expression of numerous genes required for the INFLAMMATORY response (cytokines, interferons, chemokines, AMPS, major histocompatibility (MHC) and costimulatory molecules 4 adaptive immune activation)

2) Ligand binding to TLR induces its TIR domain changes, inducing association with adaptor molecules via TIR-TIR domain interaction.

3) Myd88, MAL, TRIF, and TRAM which bind to activated TLR and recruit downstream signaling molecules

4) NF-kB signaling and IRF signaling

Question 24

(T/F) All TLRs contain a TIR domain that transmits downstream signals by recruiting one or more TIR-containing adaptor proteins. Different TLRs + adaptor proteins result in a more diverse immune response.

Answer 24

True!

Question 25

While activation of TLR signaling in ________ can lead to interferon and inflammatory cytokines, signaling from ___________ TLRs only results in inflammatory responses.

Therefore, the consequence of TLR activation is different depending on the _______, ______ _______ and ____ types.

Answer 25

Endosomes; cell-surface-localized

pathogen; TLR expression; cell

*PAMP–>TLR–>signal transduction

Question 26

TLR signalling activates NF-kB and IRF pathways. What are the functions of the pathways?

Answer 26

IRF pathway: generates an antiviral state

NF-kB: acute inflammation, stimulation of adaptive immunity

Question 27

1) Describe the protein, ubiquitin.

2) What is the result of ubiquitination (a post-translational modification)?

3) What is the difference between K48 and K63?

Answer 27

1) Ubiquitin is a highly CONSERVED 76 aa protein expressed in ALL cells and can be added to its substrate protein by UBIQUITINATION resulting in a ubiquitin chain.

2) can affect protein function: it can signal their degradation, alter their cellular location, affect their activity, and promote or prevent protein interactions.

3)

multimeric K48-linked chains of ubiquitin are recognized by PROTEASOME, which degrades these substrates.

multimeric K63-linked chains facilitate important protein-protein interactions.

Question 28

The NF-kB signalling pathway:

1) binds to a …?

2) responsible for ….?

3) belongs to a category of ….?

4) contributes to the induction of ….?

5) no contribution to …..?

Answer 28

1) specific decameric DNA sequence (ggg ACT TTC C)

2) cytokine production and cell survival

3) “rapid-acting” primary transcription factors (present in cells in an inactive state and do not require new protein synthesis to be activated)

4) pro-inflammatory cytokines, chemokines, and adhesion molecules

5) interferon production

Question 29

The NF-kB heterodimer consisting of _____ and _____ proteins is sequestered in the cytosol of unstimulated cells via __________ interactions with a class of inhibitor proteins, called _____. This inhibitor masks NF-kB protein’s ______ _______ _______.

______ phosphorylates IKKB.

Activation of IKK-complex results in the ________ of IkB at ____ specific serine residues by IKKB.

IkB is poly-ubiquitinated and degraded by the _____ proteasome, setting free the Nf-kB.

Answer 29

p65; p50; non-covalent; IkB; Nuclear Localization Signal (NLS)

TAK1

Phosphorylation; two

26S

*now Nf-kB translocates in the nucleus and binds promoters of cytokine genes.

Question 30

IRFs are held in the cytoplasm in an inactive form and only become transcriptionally active after …..?

Answer 30

being phosphorylated on serine and threonine residues located at their carboxy termini.

Question 31

Though there are 1-9 IRFs (interferon regulatory factors), which ones are particularly important in TLR signalling for transcription of interferon genes?

Answer 31

IRF3 and IRF7.

*TLR-3 in endosome binds dsRNA and signals via TRIF to induce IFN gene expression

*TLR-7 in endosome binds ssRNA and signals via MyD88 to induce IFN gene expression

Question 32

IRF3 has an essential role in the _____-dependent pathway of interferon gene induction by TLR3.

___ phosphorylates C-terminus of IRF3, causing a conformational change, leading to ________ and the unveiling of the ___________ signal.

In the MyD88-dependent pathway, IRF7 ______ ______ with MyD88 and is phosphorylated.

Answer 32

TRIF

TBK; dimerization; nuclear localization

directly interacts

Question 33

How is an anti-viral state generated?

Answer 33

When a virus goes into the endosome, the MAMPs are recognized by the TLRs (3, 7/8, 9), inducing IRF 1, 3, and 7 that induce type I interferon genes.

These proteins bind to IFN receptors on uninfected neighbouring cells and activate JAK-STAT signalling pathways, inducing expression of enzymes that block viral replication; ANTIVIRAL STATE.

If there is escape of the virus from the endosome, there are other sensors in the cells (RIG-1, etc) that induce IRFs and produce interferons.

Question 34

How can we use TLRs as antiviral therapeutic interventions?

Give examples.

Answer 34

We can increase inflammation using TLR agonists (LPS, Poly I:C, and CpG DNA) for treating viral infections or as vaccine adjuvants.

IMIQUIMOD, TLR7 agonist, is used to treat genital warts caused by human papillomavirus.

Synthetic ODNs with unmethylated CpG DNA are ligands to TLR9 (can treat hep C).

Question 35

What are adjuvants?

Answer 35

Substances that need to be administered together with purified protein antigens to elicit maximal T-cell dependent immune responses.

Important in clinical vaccine studies.

Many adjuvants in experimental use are microbial products that engage TLRs, such as mycobacteria and LPS.

Question 36

Lymphocytes require two signals for proliferation and differentiation (adaptive immune response).

What are they?

Answer 36

1. Microbial antigen binding to the antigen receptors found in the lymphocytes
2. Innate immune response to microbe

Question 37

NK cells (lymphocytes) are part of the ______ immunity.

Answer 37

Innate

Question 38

(T/F) NK cells kill infected and injured cells, and produce NF-kB that activates phagocytes.

Answer 38

False!

They produce IFN-y that activates phagocytes.

*Macrophage with phagocytosed microbes produce IL-12 and bind to NK receptors, resulting in NK production of IFN-y.

Question 39

What is the missing-self hypothesis?

Answer 39

Normal, un-infected cells (self-cells) express MHC class I molecules that bind to the inhibitory receptors on the NK cells, resulting in inactivated NK cells.

In infected cells, MHC class I molecules display peptides from viruses to cytotoxic T cells that kill them. A viral evasive mechanism from killing T cells is to down regulate MHC class I molecules. However, this means there is a lack of inhibitory signal for NK cells; NK cells detect and kill these viral infected/cancerous cells.

Question 40

(T/F) NK cell function is regulated by a balance between signals from activating and inhibitory receptors.

Answer 40

True!

Question 41

(T/F) The activating receptors of NK cells have a kinase, while inhibitory receptors have a phosphatase. The removal of the phosphate on the kinase gets rid of the activating signals.

Answer 41

True!

activating signals -> activated NK cells -> kills infected cells

Question 42

What happens to

a) virus infected cells with no class I MHC expression

b) stressed cells with induced expression of activating ligands

c) normal cells

Answer 42

a) no phosphatase to remove the phosphate of the kinase found in the activating receptor, resulting in activating signals; activated NK cell - killing of infected cell

b) ineffective removal of phosphates of the activating receptor kinase due to many activating ligands, resulting in killing of stressed cells

c) when there are MHC class I molecules, the inhibitory receptor removes the phosphates of the kinase of the activating receptor, removing the activating signals.