Autoimmunity in the Clinic

Question 1

what is autoimmunity?

Answer 1

• failure of self tolerance
• 3% of population affected, up to 10% lifetime risk
• Autoimmunity is complex damage but cells aren’t abnormal themselves, they are just behaving in the wrong way – hard to spot cells behaving badly

Question 2

what are the general features of autoimmunity?

Answer 2

B and T cell reactivity to self antigens
- frequently, autoantibodies are produced
- partial heredity: genes can be inherited that predispose you/increased risk, but need environmental factors to induce
- genetic predisposition
- environmental triggers

Question 3

why do we need to maintain tolerance?

Answer 3

Vast repertoire of antigen specific receptors carried by effector (T & B) cells, formed in an unbiased way

Question 4

how do we maintain T cell tolerance?

Answer 4

Central:
- T cells made in BM, educated in thymus
- Positive and negative selection - not 100% efficient as AIRE doesn’t present every self-antigen

Peripheral:
- ignorance - immune privilege
- Tregs = suppression, immune checkpoints
- lack of co-stimulation induces anergy or cell death (CD40/CD40L, CD28/CD80/86, CTLA-4)

Question 5

what are CTLA-4 and CD28?

Answer 5

both expressed on T cells and bind CD80/86 on APCs
- CD28 is stimulatory
- CTLA-4 is inhibitory (immune checkpoint)

Question 6

how do we maintain B cell tolerance?

Answer 6

Central:
- Made in BM and leave as naïve B cell
- Lack primary central tolerance
- deletion of B cells lacking functional BCR or if they recognise extracellular self-antigens of the bone marrow - not efficient

Peripheral
- Encounter cognate antigen in secondary lymphoid tissue
- Controlled peripherally by T cell help

Question 7

what are the mechanisms of loss of tolerance?

Answer 7

1. exposure of immune privileged sites
2. bystander activation = impaired T cell anergy/death
3. loss of function of Tregs
   - lack of immune checkpoints

Question 8

how can immune ignorance go wrong?

Answer 8

sympathetic ophthalmia
- eyes are an immune privileged site
- penetrating injury to eye leads to immune response that attacks the other eye
- Antigens within the eye are exposed to intolerant immune system – leads to autoreactivity in other eye
- Inflamed retina can lead to autoimmunity – treat with immunosuppressants

Question 9

how can T cells undergo anergy/cell death?

Answer 9

Autoreactive T cell may recognise self-antigen in presence of APC
- If lack of co-stimulatory molecules due to lack of DAMPs, but still TCR-peptide, this induces anergy or death of the T cell
- T cell no longer responsive, or is apoptosed
- Absence of co-stimulatory signal 2 = anergy or death

Question 10

how does T cell anergy/cell death go wrong?

Answer 10

bystander activation: there may be presentation of self-antigen in presence of danger signals, enabling APCs to provide co-stimulation
- this may occur under infection, near the autoreactive T cell
- signals present to activate self-reactive T cells

Question 11

what is an example of a mouse model which uses bystander activation?

Answer 11

the CIA mouse model
- injection of type II bovine collagen with Freund’s adjuvant (inactive TB in oil emulsion)
- Give mice this cocktail – mice develop arthritis and autoantibodies to their own collagen
- Freund’s provides the danger signals to stimulate co-stim on APCs for full T cell activation

Deliberate induction of bystander activation

Question 12

how are Tregs affected in autoimmunity?

Answer 12

Tregs in patients with RA express Foxp3, but lack expression of CTLA-4 – functionally deficient Tregs in RA patients

Question 13

how are checkpoint inhibitors implicated in autoimmunity?

Answer 13

Checkpoints e.g. PD-1, CTLA-4
- Checkpoint inhibitors of PD1 or PDL1 to allow T cells to recognise cancer
- But this can induce autoimmunity

Use PD-1 agonist to treat autoimmunity by increasing T cell suppression

Question 14

what is the consequence of loss of T cell tolerance?

Answer 14

Production of autoantibodies – loss of control of B cells

Question 15

how do autoantibodies cause disease?

Answer 15

1. Complement-dependent lysis e.g. in paroxymal cold haematuria (lysis of erythrocytes)
2. Opsonisation – tagging platelets or erythrocytes for phagocytosis
   - most haemolytic anaemias
   - Remove spleen and give pneumococcal vaccine – redundancy
3. Immune complexes e.g. in SLE
   - Insoluble immune complex in organs e.g. kidney – can induce organ damage
4. Receptor blockage
   - Antibodies blocking key receptors e.g. ACh receptor in myasthenia gravis
5. receptor stimulation e.g. Graves disease activating TSHR

Question 16

do autoantibodies always cause disease?

Answer 16

Autoimmune disease is often characterised by auto-antibodies - markers but may not always cause disease
- not the main driver/cause of disease
-

Question 17

when do autoantibodies cause or not cause disease?

Answer 17

antibodies to erythrocytes = haemolytic anaemia

antibodies to AChR = myasthenia gravis

antibodies to heart muscle following myocardial infarct do nothing - cleared quickly and are not adverse

antibodies in SLE are secondary to the core pathology, but are highly pathogenic
- defect of apoptotic clearance, so exposure of intracellular antigens – production of autoantibodies which drive disease manifestation

Question 18

what are examples of tissue-specific autoimmune diseases?

Answer 18

thyroid = Graves, Hashimoto

Kidney, lung = Goodpastures

Pancreas = Type 1 diabetes (autoantibodies to Islets, loss of insulin-producing cells)

Question 19

what type of hypersensitivity reactions are tissue specific autoimmune diseases?

Answer 19

type II

Question 20

are there co-morbidities in autoimmune diseases?

Answer 20

Common to have multiple autoimmune diseases
e.g. RA patient likely to have thyroid disease

Question 21

what is Hashimoto’s thyroiditis?

Answer 21

Thyroid disease:
- causes neck swelling and hoarse voice
- Destruction of thyroid gland by antibodies
- Drives hypothyroidism
- Blocks binding of TSH to its receptor via anti-TSHR IgG antibodies - stops thyroid hormone production
- antibodies also against thyroid peroxidase and thyroglobulin
- Can use extracts of thyroid hormone from animal to treat

Question 22

what do thyroid hormones do?

Answer 22

control the metabolism of the body

Question 22

what is Grave’s disease?

Answer 22

• hyperthyroidism: overactive thyroid as IgG TSHR antibody acts as agonist to mimic TSH
• Stimulates TSHR
• irregular heartbeat, tremor, anxiety, eye prominence
• Antibodies against thyroid antigens also stimulate: orbital fat cells, muscle cells, fibroblasts
• Accumulation of fat cells in eye as antibodies bind to them and induce proliferation, which can push out the eyes

Question 23

what is Goodpasture’s syndrome?

Answer 23

Antibodies to capillary basement membrane shared between kidney and lung alveoli
- Kidney destroyed by antibodies – glomerulus is broken down
- fatigue, bloody urine, oedema, oliguria
- Bleeding of lungs in the chest as the basement membrane is destroyed - cough up blood

Question 24

what are examples of systemic autoimmunity?

Answer 24

1. rheumatoid arthritis
   - joint, eye, nerve, lung, skin, vasculature
   - can cause accelerated CVD, strokes
2. SLE
   - everything: joints, skin, CNS, kidney, vasculature
   - also increased risk of heart disease
   - affects young women
3. scleroderma
   - skin, lung, vasculature, kidney, joint
   - prolonged fibrosis

SLE and scleroderma characterised by autoantibodies

Question 25

how can systemic autoimmune diseases be treated?

Answer 25

Use CD19 CART cells to deplete B cells – can reset these patients

Question 26

what are the key symptoms of RA?

Answer 26

• joint pain in hands, feet, wrists, knees
• symmetrical
• erosion of joints in the hands
• loss of cartilage and erosion of bone
• nodules(granulomas without antigen)
• lung fibrosis
• rupture or orbit - scleritis
• vasculitis (blood vessel inflammation)

Question 27

what is RA?

Answer 27

• A common chronic inflammatory joint condition
• 1% UK = 600,000 people
  direct NHS costs £560m, indirect £1.8bn* - biologics are highly expensive
• Multi-factorial aetiology – genetics and environment
• Associated in some patients with autoantibodies
• variable course with exacerbations and remissions
• inflammation leads to irreversible joint damage (erosions)
• can result in severe disability

Question 28

what is RA associated with?

Answer 28

autoantibody production (in some but not all patients)

1. rheumatoid factor
2. ACPA

Question 29

what is rheumatoid factor?

Answer 29

RF is an autoantibody to Fc receptor of antibodies
- Not useful for diagnosis as only 60% patients have this
- associated with severe, erosive RA, but no known function for pathogenesis of disease
- We all have RF as immune system can recognise antibodies as foreign - but we tolerate this
- prevalence increases with age (20% of >60s)
- Useless as it is non-specific and increases with age
- not a diagnostic test: seen in other diseases e.g. SLE, scleroderma, chronic lung infection

Question 30

what is ACPA?

Answer 30

anti-CCP (antibodies against citrullinated peptide antigens)
- arginine to citrulline
- Antibodies to modified proteins found in the joint and elsewhere
- Strongly associated with smoking in RA
- Present in ~ 60% RA
- Associated with severe, erosive disease
- More specific than RhF – less false positives
- A better diagnostic marker – but still not perfect, still only present in 60% patients

Question 31

how do ACPA correlate with RA?

Answer 31

Citrullination can predispose to loss of tolerance
- autoantibodies can occur long before disease symptom appearance (10-15 years before RA, high likelihood for break in tolerance)

Question 32

summary of autoantibodies in RA:

Answer 32

The pathological role of autoantibodies in RA is controversial (cause or effect?) – may appear but may not cause

They should not be used as screening or diagnostic tests in RA

They do give useful information in patients who have a newly presenting arthritis

They give us interesting data about the mechanisms underlying development of RA

Question 33

what genetic predisposition is involved in RA?

Answer 33

HLA-DBR1 - encodes MHC variant
- Shared epitope
- Conformation of MHCII peptide binding cleft to increase binding to certain peptides
- Commonly seen in RA patients

Question 34

why was the MHC variant found first in RA?

Answer 34

HLA associations are interesting because HLA genes code for MHC proteins which present antigen

HLA genes also happen to be some of the most studied genes

Non-biased methods of gene discovery have found strong associations in other genes

Question 35

what other genetic variants have been found to have an association with RA?

Answer 35

Manhattan plot – GWAS unbiased study
- MHC is a powerful association with RA
- Also PTPN22 (TCR signal inhibitor)

Question 36

how can genetic and environmental risk factors interact in CCP-seropositive RA?

Answer 36

HLA-DRB1 genotype causes predisposition to RA
- gene dose effect - inheriting both copies enhances risk
- 1 copy can interact with smoking or presence of another gene e.g. PTPN22
- no copies = low risk

HLA-DRB1, PTPN22 and smoking drastically increases risk – epigenetic risk of smoking

Question 37

how are risk factors different in CCP-negative RA patients?

Answer 37

In CCP-negative RA, its completely different genetic and environmental factors
- PTPN22, HLA-DRB1 and smoking have no effect
- difficult to study as these patients lack obvious biomarkers

Question 38

how does smoking increase RA risk?

Answer 38

Smoking increases citrullination in the lung – breaks tolerance in lung, and then joint
- autoantibodies to CCPs

Question 38

how can CCP positivity be useful?

Answer 38

it can help identify patients at risk
- not for diagnosis though
- helps intercept disease early on

Question 39

what is the APIPPRA trial?

Answer 39

Arthritis prevention in the pre-clinical phase of RA with abatacept
- study patients who are positive for autoantibodies and who have early symptoms of aches, but lack full cartilage erosion
- Randomised to treat with placebo or abatacept (CTLA-4-bound to IgG injected into circulation)
- inhibits autoreactive T cells by flooding system with CTLA-4
- Abatacept delays onset of disease – prevent natural development of disease