L4. Innate Immunity Continued

Question 1

What is the general role of Nod-like receptors?

Answer 1

Triggers cells to start making cytokines: signal expression of pro-inflammatory cytokines

Question 2

How do Nod-like receptors trigger cells to start making cytokines?

Answer 2

Do this by triggering assembly of inflammasomes – multi-subunit complex that cleaves inactive cytokine precursors (Inflammasome turns inactive pre-cursers of cytokines into active cytokines).

Question 3

Describe how a) active cytokine are made directly b) pro-cytokines are made and activated.

Answer 3

a. TLR: Cell recognises MAMP through TLRs on plasma membrane, activates signalling causing changes in gene expression to transcribe cytokine genes into inactive cytokine forms (important so don’t cause damage) called pro-cytokines and need to be cleaved to be activated.
>NLR: When a bacterium is taken up by phagocytosis, some MAMPs from the phagolysosome are released inside the cell and bind with NLRs (NOD-like receptors) in the cytoplasm, producing a signal to nucleus to activate cytokine transcription

b. NLRs also trigger the formation of an inflammasome (disc-like complex) which can bind a protease (caspase-1 oligomers) that cleave pro-cytokines into active cytokines (only assembled when we have infection and need to process pro-cytokines).
>So, some cytokines are released directly, others are made as inactive precursors that must be cleaved to make the active form

Question 4

What type of infections are the PRRs “Toll-like and Nod-like Receptors” useful against. why and what do they do?

Answer 4

> for bacterial infections

> As recognise bacterial components e.g. peptidoglycan, flagellin

> signal expression of pro-inflammatory cytokines

Question 5

What type of infections are the PRR “RIG-I-like Receptors” useful against, why and what do they do?

Answer 5

> for viral infections

> As can detect viral RNA produced within host cells

> Induce cells to start making interferons (cytokine sub group protecting us against viruses).

Question 6

What are the cells which often response first to infection?

Answer 6

Tissue macrophages/mast cells (sentinel cells) are often first to respond

Question 7

What 3 things do Tissue macrophages/mast cells (sentinel cells) do when being activated by an infection?

Answer 7

1. Releasing inflammatory mediators that increase blood flow and vascular permeability,
2. And releasing chemoattractants that attract phagocytes into the tissues.

3.Cytokines, small proteins that induce other cells to help deal with the infection, are also produced

Question 8

What is inflammation and what is it triggered by?

Answer 8

Inflammation, triggered by infection and tissue damage, is a critical local response to infection, allowing the phagocytes in blood to gain access to the microbes in tissues

Question 9

What are the 4 classic signs of inflammation and what causes each?

Answer 9

1. Redness
   >Caused by release of inflammatory mediators (by macrophages and mast cells)
2. Swelling
   >Dilation of local blood vessels causing swelling, blood enters and immune cells (neutrophils in first place)
3. Heat
   >Increased permeability and blood flow at site of infection or damage.
4. Pain
   >Pain is caused by stimulation of nerve endings supplying the tissues.

Question 10

What are the 5 classes of inflammatory mediators produced by sentinel cells (mast cells and macrophage) in response to tissue damage, or microbes etc? And an example for each.

Answer 10

1. Lipid mediators
   >e.g. prostaglandins stimulating dilation of blood vessels and acting on pain receptors (to cause pain)
2. Vasoactive amines
   >e.g. histamine, bradykinin cause dilation of blood vessels
3. Chemoattractants produced
   >e.g. fmet-leu-phe help phagocytes move into tissues
4. Complement proteins
   >e.g. C5a and C3a acting as chemoattractants
5. Cytokines
   >e.g. TNF

Question 11

What are the 2 types of inflammation?

Answer 11

Acute and Chronic inflammation

Question 12

What are 3 characteristics of acute inflammation?

Answer 12

> Generally beneficial in dealing with infection/injury

> Very painful

> Comes on rapidly, goes down rapidly

Question 13

What causes chronic inflammation and 2 examples?

Answer 13

> Caused by Chronic infection orover active immune system

> E.g. TB and autoimmune diseases

Question 14

How does TB and autoimmune diseases cause chronic inflammation?

Answer 14

1. Autoimmune disease as immune system never switches off as was never any immune response
2. TB survive inside macrophages, body develops chronic inflammatory response to this causing Granulomas to form (build ups of cells containing TB with wall of immune cells surrounding it)

> Both can be damaging.

Question 15

What branch of the immune system are cytokines involved with and how do they effect it?

Answer 15

Involved in initiating and controlling innate and adaptive immunity and tells immune system when to switch off

Question 16

How do cytokines work generally in 4 steps?

Answer 16

1. MAMP stimulate PRR
2. Cytokine produced by cell (e.g. sentinel cell or T cells)
3. Through paracrine signalling bind to cytokine receptor on neighbouring cell.
4. Alters transcription in target cell changing its behaviour (biological effect).

Question 17

Why are cytokines called “hormones” of the immune system?

Answer 17

Most act locally unlike hormones, but can have systemic effects

Question 18

Why is it important that most cytokines act locally?

Answer 18

Important as can cause damage if activity goes unchecked.

Question 19

What type of cells can produce cytokines?

Answer 19

Can be produced by many cell types in response to immune activation (Not just T cells, innate immune cells and fibroblasts/ epithelial cells can also make cytokines).

Question 20

Why is the expression of cytokines and their receptors is tightly regulated?

Answer 20

Can cause damage to own tissues if not

Question 21

How are cytokines classified?

Answer 21

CAN be grouped into families on basis of structural similarities (but family members may have distinct functions)

Question 22

What are 5 families of cytokines, what are their roles and an example for each?

Answer 22

1. IL-1 family:
   >most produced as inactive precursors that must be cleaved by inflammasomes, important in inflammation
2. Haematopoietin superfamily:
   >includes factors involved in leukocyte differentiation e.g. GM-CSF but also IL-2, IL-4, IL-6 (important in T cell responses).
   >Important for generation new white blood cells from bone marrow
3. Interferons:
   >involved in responses to viruses
4. TNF family
   >(e.g. TNFα = tumour necrosis factor): many are transmembrane proteins that are shed, important in inflammation.
   >TNF is very toxic, at low conc injected will kill a person, very tightly regulated in our body but can kill tumours.
5. Chemokines:
   >involved in cell movement (e.g. IL-8 a.k.a CXCL8)
   >IL-8 now called CXCL8, induces neutrophils to move out of blood stream into tissues.

Question 23

Are the cytokine receptors for cytokine subfamilies similar?

Answer 23

Cytokine receptors for the various subfamilies also tend to have similar structures and to signal in a similar way

Question 24

What are 5 cytokines that might be made by tissue-resident macrophage (very good at making cytokines) in early stages if immune response and their role?

Answer 24

a. IL-1
>Pro-inflammatory
>Also act on hypothalamus regulating temp inducing fever response (fever response is beneficial in activating immune cells and killing or slowing growth of some pathogens)

b. TNF-alpha
>Important inflammatory mediator, good at causing acute inflammation
>Toxic at high amounts
>Main cytokine involved in sepsis (bacteria in blood stream) but TNF causes more damage than the bacteria.

c. IL-6
>Activates parts of adaptive immune system (B and T cells)
>Also induces fever response

d. CXCL8
>Causes neutrophils to move out of blood stream and into tissues

e. IL-12
>Can activate NK cells, involved in viral or bacterial infection when inside host cells
>Helps activate T cells as a part of adaptive immune response.

Question 25

What does every viral infected cell produce and what does it do?

Answer 25

> Viral infection induces the production of interferons

> Interferons Interfere with viral replication so viruses struggle to replicate in neighbouring cells.

Question 26

What are the 2 types of interferons and an example for each?

Answer 26

1. Type I interferons: IFN-α ; IFN-β
2. Type II interferon: IFN-γ

Question 27

What are the 4 functions of Type I interferons (IFN-α ; IFN-β)?

Answer 27

1. Induce resistance to viral replication in all cells.
2. Increase MHC class I expression in all cells.
3. Activate NK cells to kill virally infected cells.
4. Induce chemokines to recruit adaptive lymphocytes.

Question 28

How do IFN-α ; IFN-β (Type I interferons) induce resistance to viral replication in cells?

Answer 28

1. Induce expression of endoribonuclease that degrades viral RNA
2. Induce expression Protein kinase that phosphorylates eukaryotic initiation factor 2, inhibiting protein translation (most proteins being made by this cell will be viral at this point)

Question 29

Why do IFN-α ; IFN-β (Type I interferons) increase MHC class I expression in all cells?

Answer 29

MHCI proteins present endogenously derived peptides (which can include viral or tumor antigens) to the immune system. As infected cells or tumour cells will present foriegn peptide to cytotoxic T cells, will cause cell death (important for adaptive immunity).

Question 30

What type of cells express MHC class I proteins?

Answer 30

MHCI expressed by all nucleated cells

Question 31

What cells can make type I interferons (IFN-α ; IFN-β) and which cells are more effective at this and why?

Answer 31

> Many cell types make type I interferons after viral infection. Induce expression of interferon-stimulated genes (ISGs)

> Some cell types (e.g. dendritic cells) are specialised for this – express high levels of endosomal TLRs e.g. TLR3 and TLR9 recognising double stranded viral RNA.

Question 32

Which cells produce type II interferons (IFN-γ)?

Answer 32

Made by more specialised cells: neutrophils, NK cells, T cells

Question 33

What is the role of type II interferons (IFN-γ)?

Answer 33

> Primary role in adaptive immunity, increases expression of MHCI and MHCII

1. MHCI increase helps induce cytotoxic T cells (as if a cell is infected, as MHCI presents peptides from inside, will present more foriegn peptide increasing chances of CD8+ve binding)
2. MHCII increase induces T helper cells

Question 34

What is the purpose of T-helper cells producing IFN-γ?

Answer 34

IFN-γ made by T helper cells activates macrophages in responses to intracellular pathogens

Question 35

What is meant by the innate and adaptive immune systems being interdependent?

Answer 35

They are dependent on each other.

Question 36

Why are adaptive and innate immunity interdependent?

Answer 36

As they co-evolved together.

Question 37

How does the innate immune system influence the adaptive immune system?

Answer 37

Innate immune responses initiate adaptive responses (antigen presentation) and different cytokines can “steer” adaptive immune responses by activating different T cell subsets, promoting the production of different antibody classes

Question 38

How does the adaptive immune system use the innate immune system?

Answer 38

Adaptive responses use elements of innate immunity to eliminate pathogens e.g. classical pathway of complement, activation of macrophages by T cell cytokines, antibodies can help NK cells recognise infected cells, mast cells to respond to parasites.