Lecture 26 - Rheumatoid Arthritis - Synovium Flashcards Preview

BIOM30002 - M2M > Lecture 26 - Rheumatoid Arthritis - Synovium > Flashcards

Flashcards in Lecture 26 - Rheumatoid Arthritis - Synovium Deck (64):
1

What are the layers of healthy synovium?

• Intima (internally)
• Subintima (externally)

2

Describe the intima

• Interface between joint cavity and subintima
• 1-3 cell layers deep
• Made up of synoviocytes

3

Describe the subintima

• Connective tissue
• Becomes denser closer to the joint capsule
• Contains blood vessels, lymphatics, and nerves

4

Describe the supply to the synovium

Subintima receives:
• Blood supply
• Lymphatic vessels
• Nerve innervation

5

What are the different types of synovial tissue?

• Areolar
• Fibrous
• Fatty

6

Describe Areolar synovium

• Intima
• Continuous layer of lining cells
• Often see villi formation

7

Describe fatty synovium
Where is it found?

• Mostly found in fat pads

• Under the intima are adipocytes
• Superficial net of capillaries among the adipocytes

8

Where is Fibrous synovium found?

Layer of cells on a ligament or tendon

9

What are the functions of healthy synovium?

1. Facilitation of movement
• Non-adherent
• Provides lubricants that minimise wear and tear

2. Synovial fluid production

3. Chondrocyte nutrition
• Solutes from synovial fluid diffuse to chondrocytes

10

What are the lubricants in the synovium?

• Hyaluronan
• Lubricin

11

What is hyaluronan?
What are its functions?

• Huge polysaccharide
• Maintains synovial fluid viscosity
• Shock absorption

12

What is Lubricin?
What are its functions?

• Mucin-like proteoglycan

• Protects cartilage surfaces from protein deposition and adhesion
• Inhibits synovial cell overgrowth

13

What are the cell populations in the healthy Intima?

1. Type A synoviocyte
• Macrophage-like
• 20%

2. Type B synoviocyte
• Fibroblast-like
• 80%

14

What are the functions of Type A synoviocytes?

• Phagocytosis
• Clearance of debris in joint
• Recognition of immune complexes through expression FcγR

15

What are the functions of Type B synoviocytes?

Production of:
1. Cartilage
• Collagen
• Fibronectin

2. Synovial fluid components:
• Hyaluronan
• Lubricin

16

What is the target for tissue inflammation in RA?

At what point in disease does it become inflamed?

The synovium

Becomes inflamed very early in disease

17

Describe the Intima when inflamed

• Hyperplasia of synoviocytes
→ up to 12 cells thick
• Proliferation of Type A synoviocytes (outnumber type B)

18

Describe the processes occurring in the synovium when inflamed

• Hyperplasia of synoviocytes
• Infiltration of inflammatory cells
• Neovascularisation
• Ectopic lymphoid neogenesis
• Deposition of fibrin

19

Which inflammatory cells infiltrate the synovium in RA?

What brings about the infiltration?

Where do they infiltrate into?

1. Which cells:
• Macrophages
• T cells
• B cells

less commonly: neutrophils

2. Recruitment:
• Release of chemokines from inflamed synovial tissue
• Expression of adhesion molecules to retain the cells

3. Where:
• Infiltrate into the Subintima

20

Where does neovascularisation occur in RA?

In the subintima

21

Describe ectopic lymphoid neogenesis

Occurs in synovitis in RA

Germinal centres form in the synovium

22

What is the Pannus?

Of what is it composed?

What does it do?

• Inflamed synovial tissue
• Creeps over the cartilage and bone tissue of the joint (v. important)

• Hypoxic microenvironment

Contains:
• Fibroblast-like cells
• Macrophages
• Fewer immune cells than peripheral inflamed synovial tissue

Function:
• Release of factors that destroy articular cartilage and bone

23

What is the oxygen status of the Pannus?

Hypoxic

24

What happens to the ratio of the various synoviocytes in RA inflammation?

Type A outnumber Type B

25

Describe the phenotype of Type A synoviocytes in RA

"Activated phenotype"

• Expression of phagocytic markers
• Increased expression of MHC II → increased Ag presentation
• Production of:
- Pro-inflammatory cytokines
- Chemokines
• Possible transdifferentiation into osteoclasts

26

Which cells produce pro-inflammatory cytokines in inflamed synovium?
Which cytokines are they?

Activated Type A synoviocytes

• TNF
• IL-1
• IL-6

27

What is the function of osteoclasts?

Bone resorption

28

Describe the role of Type B synoviocytes in RA

Production of:
• Pro-inflammatory cytokines
• Chemokines
• Matrix-metalloproteinases (MMP)
• Factors that bring about bone destruction
• Factors that inhibit bone formation

29

Which cells produce chemokines in inflamed synovium?

• Type A synoviocytes
• Type B synoviocytes

30

What is the function of MMPs?

(Matrix-metalloproteinases)
• Degradation of the ECM

31

Which factors bring about bone destruction?

• TNF
• RANKL

32

Which factors inhibit bone formation?

• TNF
• DKKs
• sFRPs

33

Which is the predominant lymphocyte in inflamed synovium?

Th17

34

Describe the role of T cells in RA inflammation

Th17:
• Produce IL-17
• Express RANKL

Treg:
• Present, but non-functional
• Reduced expression of IL-10 and IL-4

35

Which cytokine skews Th differentiation into Th17?

IL-6

36

Which cytokine does Th17 produce?
What are the effects of this?

1. IL-17
• Matrix degradation
• Activation of osteoclasts
Induces other cells to express:
• RANKL
• Pro-inflammatory cytokines

2. IL-22
• Activation of osteoclasts

37

Describe the role of B cells in RA inflammation

Describe their presence

• Presence is variable (depends of stage of disease?)

Function:
1. Production of auto-antibodies:
• ACPA
• RF
• anti-collagen type II antibodies

2. Antigen presentation to CD4+ T cells
→ cytokine release

3. RANKL secretion

38

What type of molecule is RANKL?

Cytokine, member of the TNF superfamily

39

Which general categories of molecules are release by cells in inflamed synovium?

• Cytokines
• Chemokines
• Growth factors

40

Where is TNF?

• Initially membrane bound
• Cleaved by TACE (TNF-alpha converting enzyme)
• Now soluble

41

What are the receptors for TNF?
Compare expression of these

1. TNFRI:
• Constitutive expression

2. TNFRII:
• Induced expression

42

What are the sources of TNF in RA synovium?

Predominantly: Activated macrophages

• Activated fibroblast-like synoviocytes
• T cells

43

What are the functions of TNF in RA?

• Osteoclast activation
• Osteoblast inhibition

• Proinflammatory cytokine release
• Recruitment of inflammatory cells
• Angiogenesis

44

What are the isoforms of IL-1?

Compare their locations

1. IL-1α
• Cytosolic form
• Stored in cytoplasm

2. IL-1β
• Inducible form
• Secreted and cleaved into active form by ICE

45

Which molecule activates IL-1β?

ICE: IL-1 converting enzyme

IL-1β → active form

46

Which molecules are important in the regulation of IL-1?

Describe how they function

1. Soluble IL-1 receptors: sIL-1R
• Act act decoy receptors
• Bind soluble IL-1 in extra-cellular space, so that it can't bind the real receptor

2. IL-1 receptor antagonist: IL-1Ra
• Binds the membrane bound IL-1R so that IL-1 can't bind

47

What are the sources of IL-1 in RA synovium?

• Macrophages

• Type B synoviocytes
• Endothelial cells
• Neutrophils
• Lymphocytes

48

What are the roles of IL-1 in RA?

1. Cell activation:
• Leukocyte activation
• Endothelial activation
• Fibroblast activation

2. Proinflammatory expression of cytokines and chemokines

3. MMP production by chondrocytes and synovial fibroblasts

4. Production of factors required for osteoclast differentiation
→ bone resorption

49

Describe the location and mode of action of IL-6

• Present in extra-cellular space in soluble form

1. Binds:
• Membrane bound IL-6R
• Soluble IL-6R
2. IL-6:IL-6R associate with gp130 homodimer
3. Response in cell

50

What are the sources of IL-6 in RA synovium?

• Type B synoviocytes

• Macrophages
• T cells

51

High levels of pro inflammatory cytokines in RA are detectable in...

• Synovial fluid
• Serum

(IL-6, TNF, IL-1)

52

What are the roles of IL-6 in RA?

• Acute phase response in liver → systemic inflammation

• B cell Ig production

• Differentiation into Th17

• Pro-inflammatory cytokine production in fibroblasts and macrophages

• Osteoclast differentiation via RANKL

53

What does the acute phase response in the liver bring about?
What brings about this response

IL-6 → Acute phase Response → Systemic inflammation

54

Which animal models are used to research RA?

What have animal models told us?

Murine models:
• CIA
• h.TNF.Tg

Why:
• Hard to study RA pathogenesis in humans

What murine models have shown us:
• Identification of cellular and molecular mechanisms driving RA
• Enables pre-clinical studies
• Validation of therapeutic targets for the treatment of RA

55

What is the CIA model?

Describe how it is performed and the progression to disease

Collagen-induced arthritis

Day 0: Immunisation of foreign source of Type II collagen / FCA (by intradermal injection)

→ Systemic activation of lymphocytes
→ anti-collagen Ab production

Day 21: booster injection at base of tail

→ Local synovitis
→ Inflammatory infiltrate into synocium

Day 30:
→ Significant local synovitis
→ Destruction of cartilage and bone

56

What is FCA?

Freunds Complete Adjuvant

Part of the solution used to immunise mice against collagen in the CIA rodent model

57

What are the pros and cons of the CIA model?

1. Pros:
• Symmetrical arthritis affecting knees and paws
• Synovitis
• Dependent on B and T cells
• TNF and IL-1 expression elevated
• RF reported to be produced

2. Cons:
• Disease susceptibility dependent on expression of certain classes of MHC class II
→ Only certain mice are susceptible: DBA/1
• Anti-collagen Ab produced, unlike in humans
• Timing of disease onset is variable, large experiment groups required

58

What is the hTNF.Tg mouse?

What does the mouse experience?

What does this tell us about RA?

Genetic mouse model of RA

Mouse over expresses human TNF

• Arthritis of knees and paws
• Synovial hyperplasia
• Inflammatory cell infiltrate
• Full blown arthritis by 10 weeks
• Pannus formation
• Cartilage destruction
• Focal bone erosion
• System bone loss

• Disease severity reduced with TNF blockage

• KO of IL-1 or IL-1R results in no disease!

Conclusions:
• RA disease process driven by TNF

59

What are the pros and cons of the hTNF.Tg mouse?

1. Pros:
• Reliable, robust arthritis
• Arthritis is chronic
• Allowed investigation of TNF inhibition in treatment

2. Cons:
• TNF dependent, but the other cytokines are not so important in this model
• Not dependent on T and B cells

60

In general what are the pros and cons of rodent models of RA?

1. Pros:
• Pre-clinical identification
• Validation of therapeutics targets

2. Cons:
• Most animal models are dependent on IL-1

IL-1 is not so important in human disease:
→ mAb against IL-1 not so effective, but this may have just been an issue with the mAb
→ TNF blockade very powerful

61

Which molecule prevents protein deposition on articular cartilage?

Lubricin

62

Which mouse strain is most susceptible to RA disease in the CIA model?

DBA/1

63

Which cells make the synovial fluid?

Synovial membrane, specifically, the type B synoviocytes

64

Drawbacks of murine models of RA:

"Most animal models are dependent on ... expression"

IL-1