Lecture 25 - Synovium in Health and Rheumatoid Arthritis

Question 1

Synovium

Answer 1

Thin membrane that extends from skeletal tissue at the interface between cartilage and bone, and lines the capsule of diarthroidal joints

Question 2

Layers of synovium
1)
2)

Answer 2

1) Intima

2) Subintima

Question 3

Intima
1)
2)
3)
4)

Answer 3

1) Inner layer of synovium.
2) Made up of synoviocytes (type 1 and 2)
3) 1-3 cells deep
4) Interface between subintima and joint cavity

Question 4

Subintima
1)
2)
3)

Answer 4

1) Lies between the joint capsule and intima
2) Becomes more dense as it approaches the joint capsule, bone, cartilage
3) Contains blood vessels, lymphatic vessels , nerves

Question 5

Three different types of synovial tissue

Answer 5

1) Areolar
2) Fibrous
3) Fatty

Question 6

Areolar synovial tissue
1)
2)
3)

Answer 6

1) Continuous layer of synoviocytes lining it
2) Capillaries immediately below intima
3) Contains small arterioles, venules, lymphatic vessels

Question 7

Fibrous synovial tissue
1)
2)

Answer 7

1) Layer of cells on a ligament or tendon

2) Hard to distinguish histologically from fibrocartilage

Question 8

Fatty synovial tissue
1)
2)

Answer 8

1) Mostly found in fat pads

2) Underlying intima is a network of capillaries in between adipocytes

Question 9

Functions of a healthy synovium
1)
2)
3)
4)

Answer 9

1) Facilitates movement
2) Produces synovial fluid
3) Supplies chondrocytes with nutrition
4) Type 1 chondrocytes phagocytose material

Question 10

How does a healthy synovium facilitate joint movement
1)
2)
3)

Answer 10

1) Synovium is highly deformable and movable
2) Provides lubricants
3) Non-adherent

Question 11

Lubricants secreted by synovium
1)
2)

Answer 11

1) Lubricin

2) Hyaluronan

Question 12

Lubricin
1)
2)
3)

Answer 12

1) Mucin-like proteoglycan
2) Protects bone and cartilage surfaces from protein deposition and cell adhesion
3) Inhibits synovial cell overgrowth

Question 13

Hyaluronan
1)
2)
3)
4)

Answer 13

1) High molecular weight polysaccharide
2) Maintains synovial fluid viscosity
3) Effective shock absorber
4) Prevents leakage of synovial fluid

Question 14

How do chondrocytes receive nutrition?

Answer 14

Solute diffusion through synovial fluid

Cartilage is avascular

Question 15

Proportion of type A synoviocytes to type B in healthy synovium

Answer 15

20% type A, 80% type B

Question 16

Type B synoviocytes
1)
2)
3)

Answer 16

1) Fibroblast-like synoviocytes
2) Produce lubricin and hyaluronan
3) Produce collagen and fibrin

Question 17

Type A synoviocytes
1)
2)
3)

Answer 17

1) Macrophage-like synoviocytes. Tissue-resident macrophages
2) Clear debris from joint
3) Express FcgammaR

Question 18

Surface marker used to identify type B synoviocytes

Answer 18

CD55

Question 19

Surface marker used to identify type A synoviocytes

Answer 19

CD68

Question 20

When in RA does synovial inflammation present?

Answer 20

Very early

Question 21

Characteristics of RA synovium
1)
2)
3)
4)
5)

Answer 21

1) Intima expands from 1-3 cells thick to 12 cells thick (hyperplasia)
2) Infiltration of inflammatory cells into subintima (T cells, B cells, neutrophils)
3) Neovascularisation
4) Ectopic lymphoid neogenesis
5) Deposition of fibrin in active disease

Question 22

Pannus

Answer 22

In RA where the inflamed synovium creeps over the bone and cartilage

Question 23

Features of pannus
1)
2)
3)
4) 
5)

Answer 23

1) Differs histologically from inflamed synovium away from bone and cartilage
2) Rich in fibroblasts
3) Macrophages
4) Fewer immune cells than inflamed synovium away from bone and cartilage
5) Hypoxic micro-environment

Question 24

What do cells within the pannus do?

Answer 24

Release factors that destroy articular cartilage and bone

Question 25

``` Type A synoviocytes in RA synovium 1) 2) 3) 4) 5) ```

Answer 25

1) Outnumber type B synoviocytes 2) Express active phenotype (high phagocytic marker expression, high MHCII expression) 3) Release pro-inflammatory cytokines (TNFa, IL-1, IL-6) 4) Release chemokines 5) Might trans-differentiate into osteoclasts

Question 26

``` Type B synoviocytes in RA synovium 1) 2) 3) 4) 5) 6) ```

Answer 26

1) Mediators in inflammation in RA joint 2) Release pro-inflammatory cytokines (TNFa, IL-1, IL-6) 3) Chemokine release 4) Release matrix-degrading enzymes that break down cartilage (EG: matrix-metalloproteinases) 5) Release factors that lead to bone destruction (TNF, RANKL) 6) Release factors that inhibit bone reformation (TNF, DKKs, sFRPs)

Question 27

Predominant lymphocyte in RA synovium

Answer 27

CD4+ T cell

Question 28

Role of Th17 in RA 1) 2)

Answer 28

1) Express RANKL | 2) IL-17 induces release of other pro-inflammatory cytokines, and RANKL release

Question 29

What induces Th17 differentiation in RA?

Answer 29

IL-6 release

Question 30

Role of Treg in RA 1) 2)

Answer 30

1) Present in synovial tissue, but non-functional | 2) Don't release IL-14, IL-10

Question 31

``` Role of B cells in RA 1) 2) 3) 4) 5) ```

Answer 31

1) Variable presence in RA patients 2) Local production of autoantibodies (RF, ACPA) 3) Source of RANKL 4) Can present antigens to CD4+ T cells 5) Produce antibodies in response to T cell activation by APCs

Question 32

Cytokines that play a critical role in RA pathogenesis

Answer 32

IL-1, IL-6, TNFa

Question 33

How is TNFa released? 1) 2) 3)

Answer 33

1) Initially a membrane-bound protein 2) Cleaved from cell membrane by TNFa converting enzyme (TACE) 3) Both membrane-bound and soluble forms are active

Question 34

Types of TNFa receptors 1) 2)

Answer 34

1) TNFRI - Constitutively expressed | 2) TNFRII - Induced expression

Question 35

``` Roles of TNFa in RA 1) 2) 3) 4) 5) 6) 7) 8) ```

Answer 35

1) Pro-inflammatory cytokine release 2) Hepcidin production 3) Osteoclast activation 4) Chondrocyte activation 5) Angiogenesis 6) Leukocyte accumulation 7) Endothelial cell activation 8) Chemokine release

Question 36

``` Pro-inflammatory cytokines induced by TNFa in RA 1) 2) 3) 4) ```

Answer 36

1) IL-1 2) IL-6 3) IL-23 4) GM-CSF

Question 37

What are hepricidins?

Answer 37

Acute phase proteins made in the liver | EG: C-reactive protein

Question 38

What does TNFa induce chondrocytes to do in RA?

Answer 38

Produce matrix-metalloproteinases --> Leads to cartilage destruction

Question 39

What does TNFa make leukocytes do in RA?

Answer 39

Increase MHCII expression

Question 40

Two isoforms of IL-1

Answer 40

IL-1alpha, IL-1beta

Question 41

IL-1alpha

Answer 41

Cytosolic form of IL-1 | Stored in cytophasm of some cells

Question 42

IL-1beta 1) 2)

Answer 42

1) Inducible form | 2) Secreted, then cleaved into active form by IL-1 converting enzyme (ICE)

Question 43

How is IL-1 activity regulated?

Answer 43

By endogenous inhibitors

Question 44

IL-1 endogenous inhibitors 1) 2)

Answer 44

1) Soluble IL-1 receptors (act as decoy receptors) | 2) IL-1 receptor antagonist (competes for IL-1R binding with IL-1)

Question 45

What determines the effect of IL-1 signalling?

Answer 45

Balance between IL-1, and IL-1 inhibitors (soluble IL-1 receptors, IL-1 receptor antagonist)

Question 46

``` Sources of IL-1 in RA 1) 2) 3) 4) 5) ```

Answer 46

1) Macrophages 2) Type B synoviocytes 3) Endothelial cells 4) Lymphocytes 5) Neutrophils

Question 47

``` IL-1 roles in RA 1) 2) 3) 4) ```

Answer 47

1) Activates leukocytes, synovial fibroblasts, endothelial cells 2) Induces expression of chemokines, cytokines 3) Induce metalloproteinase production by type B synoviocytes 4) Induce expression of RANKL

Question 48

Unsuccessful RA treatment that targeted IL-1R

Answer 48

Anakinra (IL-1R antagonist)

Question 49

IL-6 receptors

Answer 49

Either soluble or membrane-bound

Question 50

How does IL-6 induce effects?

Answer 50

IL-6/IL-6R complex bind to gp130 homodimer on cell surface

Question 51

IL-6 sources in RA 1) 2) 3)

Answer 51

1) Macrophages 2) Type 2 synoviocytes 3) T cells

Question 52

``` IL-6 effects in RA 1) 2) 3) 4) 5 ```

Answer 52

1) Increases acute-phase protein release from liver 2) Increases Ig release by B cells 3) Promotes Th17 differentiation 4) Increases cytokine production by type B synoviocytes, macrophages 5) Induces RANKL

Question 53

Why is the study of human RA pathogenesis limited?

Answer 53

Only observe people with active disease.

Question 54

Most common animal model of RA

Answer 54

Collagen-induced arthritis

Question 55

How is collagen-induced arthritis induced?

Answer 55

Immunise mouse with foreign source of collagen II, Freund's complete adjuvant at base of tail

Question 56

How do genetics affect collagen-induced arthritis?

Answer 56

A lot. DBA/1 mouse strain most susceptible. Inducible in C57B6, but less severe disease

Question 57

Rodent collagen-induced arthritis timeline 1) 2) 3)

Answer 57

1) Day 0 - Intradermal injection at base of tail with foreign type II collagen, Freund's complete adjuvant. Leads to systemic B cell, T cell activation, collagen Ab production 2) Day 21 - Booster of foreign type II collagen, Freund's complete adjuvant. Leads to local synovitis, invasion of synovium with inflammatory cells 3) Day 30+ - Significant local inflammation within affected joint, destruction of bone and cartilage

Question 58

``` Pros of collagen-induced arthritis model 1) 2) 3) 4) 5) ```

Answer 58

1) Symmetrical inflammation affecting knees and paws. 2) Synovial inflammation leading to destruction of bone and cartillage 3) B and T cell infiltration, high expression of MHCII 4) TNFa, IL-1b levels elevated. If either of these are inhibited, reduces symptoms 5) Rheumatoid factor is produced

Question 59

Cons of collagen-induced arthritis 1) 2) 3)

Answer 59

1) Susceptibility is dependent on certain HLA types. Therefore only certain mouse strains can be used 2) Timing to disease is variable. Therefore large numbers of mice are required 3) Anti-collagen antibodies are produced, which aren't normally present in RA

Question 60

Transgenic mouse for RA model

Answer 60

hTNF.Tg mouse | Human TNF transgenic mouse

Question 61

``` hTNF.Tg mouse features 1) 2) 3) 4) ```

Answer 61

1) Genetically-engineered to overexpress human TNF 2) Develops arthritis spontaneously, affecting knees and paws 3) Blocking TNF reduces disease severity 4) Dependent on IL-1/IL-1R expression

Question 62

Timeline of hTNF.Tg mouse disease 1) 2) 3)

Answer 62

1) 3-4 weeks of age - Synovial hyperplasia, inflammatory cell infiltrates 2) 10 weeks - Arthritis 3) Inflammation, pannus formation, cartilage destruction, focal bone erosion, systemic bone loss

Question 63

Pros of hTNF.Tg mouse model 1) 2) 3)

Answer 63

1) Chronic arthritis 2) Reliable, robust development of arthritis (synovial inflammation, cartilage, bone loss) 3) Useful to test effect of TNF inhibition on bone loss

Question 64

Cons of hTNF.Tg mouse model 1) 2)

Answer 64

1) Even though IL-1 is essential to arthritis, this is a TNF-driven model. Could discount the effects of other cytokines 2) Arthritis not dependent on T or B cells, which are important in RA

Question 65

Common issue with animal RA models

Answer 65

Very dependent on IL-1 expression. | IL-1 inhibition in animals has been very effective at controlling RA, but less effective in humans.