Autoimmunity Flashcards

1
Q

What defines autoimmunity?

A
  • Generation of adaptive immune cell receptor diversity comes with the danger of producing cells that are able to strongly bind SELF
  • If these SELF-specific T or B cells which recognize autoantigens are not checked, then the result is autoimmunity
  • Leads to serious tissue/organ damage and possibly death if not treated 

    *Autoimmune disorders are an adaptive response, not innate
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What are 3 examples of autoimmune disorders?

A
  1. Rheumatoid arthritis → autoreactive lymphocytes reacting to Ag to the joints
  2. Systemic lupus erythematosus → auto-ab generated to DNA are deposited in the kidney
  3. Graves’ disease → Auto-Ab against thyroid hormone receptor, too much thyroid hormone
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Which of the following is an autoimmune disorder?
1. Antibodies generated against cellular DNA leading to kidney failure
2. Chronic production of IL1-beta leading to intermittent fever
3. Macrophages located in plaques contributing to tissue damage in heart disease (atherosclerosis)

A

Answer: 1. Antibodies generated against cellular DNA leading to kidney failure

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What experiment first showed autoimmunity?

A

Auto-ab bind to RBC upon cold exposure → activate complement → RBC get lysed

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What defines immunological tolerance vs self-tolerance? What defines breaking tolerance?

A

A state of functional unresponsiveness for a particular antigen
- Cells are not there or cells are there but not responding

Breaking Tolerance → making the immune system responsive to an antigen
Breaking Tolerance to self-antigen → Autoimmunity

Tolerance is an active process and tolerance to self is an essential feature of the immune system
Self-tolerance protects an individual from potentially self- reactive lymphocytes 


How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What defines central tolerance?

A

Deletion of the T- and B-cell clones before the cells are allowed to mature if they possess receptors that recognize self Ags with greater than a threshold affinity.
- Clonal deletion during lymphocyte development

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What defines peripheral tolerance? What are 3 mechanisms?

A

Deletion or rendering anergic lymphocytes that possess receptors reacting with self Ags.

Self is detected:
1. Suppression by regulatory T cells
2. Anergy
3. Activation induced cell death

Self not detected or not accessible:
1. Ignorance

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What are different levels of tolerance?

A
  1. Individual choice → at level of individual cells
  2. Committee governance → interaction between other cells (with DCs)
  3. Governance by police → Specific reg cells that shut down autoreactive processes (Tregs)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What antigens are presented in the thymus to educate T cells? How is tolerance to peripheral tissue-specific antigens (TSA) achieved?

A
  1. Self-proteins are presented → membrane channels, house keeping proteins involved in cell division/maintenance (this is limited to cells and genes that can be expressed in the thymus)

Achieving tolerance to peripheral tissue-specific antigens (TSAs) → TSA expression in mTECs:
2. AIRE: autoimmune regulator

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is AIRE? What is the effect of lack of AIRE?

A

Autoimmune Regulator expressed in mTECs
- A crucial transcriptional regulator which can promote the expression of thousands of TSAs

Lack of AIRE causes autoimmune polyglandular syndrome type 1 (APS-1) → autosomal recessive disease in humans

Taking self-reactive T cell from mouse that has APS-1 → you would transfer autoimmunity if you transfer that T cell
Autoimmune component = cell intrinsic
*Expression of Aire is specific to medullary region (where they undergo negative selection as developping, can generate lots of self-proteins in the thymus that would not normally be made

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What are mimetic cells?

A

Mimetic cells are specialized mTECs that present tissue-restricted antigens
Mimicking peripheral cell counterparts of other epithelium

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is T cell fate defined by?

A

T cell fate in the thymus is determined by the strength of the signal transmitted by the T cell receptor (avidity/affinity)

Big number of T cells generated are fltered out because they don’t recognize peptide:MHC (death by neglect = majority!!) → After selection ~ 5% of T cells you make a making it out of the thymus

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Does central tolerance get rid of all self-reactive T cells? Descrive the experiment.

A

What was thought was that was that negative selection efficiently deletes self-reactive T cells and peripheral tolerance mechanisms regulate only a small number of T cells

Actually, negative selection is very incomplete and many T cells escape deletion
Experiment: CD8 T cells recognizing a Y chromosome specific antigen (SMCY, self for males, foreign for women) is only 3x greater in women than in men.
- A large fraction (1/3) of SMCY-specific CD8 T cells are not deleted in men 


How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

How does central tolerance involve in the case of B cells?

A

Immature B cells expressing an autoreactive receptor recognizing a multivalent self antigen can undergo receptor editing

IgM cross-linking results in IgM downregulation, RAG re-expression and light-chain gene rearrangement

B cells remaining autoreactive undergo clonal deletion

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What conditions induce anergy in T cells?

A

T cell receptor binding to peptide-MHC on a cell that does not express the co-stimulatory factor B7, results in a long-lasting non-responsive state called anergy

Once anergic, no cell division upon antigen stimulation + costim (even when full signal)

This is dependent on the way DCs were activated (if fully activated or not)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What experiment showed the existence of Tregs?

A
  1. Take CD25+ and CD25- T cells from a WT mouse
    *Nude mice don’t have a thymus

Inject in group 1 of nude mice → CD25- T cells → autoimmunity
Inject in group 2 of nude mice → CD25+ and CD25- T cells → healthy

Showed that there was a subset of CD25+ T cells that where required for self-tolerance

17
Q

What transcription factor defines Tregs?
What do these cells develop from?

A

FoxP3
FoxP3+ Tregs develop from CD4 T cells that have a higher reactivity for self antigen than conventional T cells

18
Q

What is the effect of a mutation in FoxP3?
Give an example of syndrome.

A

Mutations in FoxP3 cause a human disease with aggressive and lethal lymphoproliferative syndrome characterised by multisystem autoimmunity

IPEX: Immunodysregulation, Polyendocrinopathy, Enteropathy, X-linked syndrome

19
Q

What are the different mechanisms of action of T regs to suppress effector T cells responses?

A
  1. Secretion of immuno-suppressive cytokines
    ex: TGFbeta
  2. Metabolic disruption
    - CD25 receptor on Tregs have high affinity with IL-2 → Mop-up IL-2 which is critical for survival of effector T cells, expansion and division → T cells undergo cell death without iL-2
  • CD39 and CD73 are exonuclease → generate adenosine → act on receptor to dampen effector T cells phenotype (immunosuppressive effect)
  1. Inhibition of dendritic cell maturation and function
    - Through CTLA-4-4:CD80/86 → DC produce IDO → immunosuppressive cytokine
    *CTLA-4 on Tregs
  2. Cytolysis
    - Release of Granzyme A or B to lyse and kill effector T cells
20
Q

Where are Tregs found in the lymph nodes?

A

In the deep t cell zone, colocalized with other T cells

21
Q

What is involved in activation-induced cell death as a mechanism of peripheral tolerance?

A

Following clonal expansion of effector T cells when pathogen is cleared, effector cells undergo apoptosis and only a small pool of memory T cells remains

Activation induced Fas/FasL expression (both expressed by T cells) → Autocrine and paracrine apoptosis

22
Q

What is ALPS?
(Autoimmune Lymphoproliferative Syndrome)

A

Autosomal dominant disorder where defect in T cell receptor induced apoptosis leads to non-malignant T cell division
*problem in peripheral activation induced cell death

Unchecked cell division can result from stimulation by self or foreign antigens

23
Q

What does ignorance imply as a mechanism of peripheral tolerance?

A

Antigens that are not accessible or presented to T cells induce neither tolerance nor activation = T cells are ignorant

Antigens to which this applies in particular are those that are in immunologically privileged sites**

If the ignorant T cells are activated elsewhere, then the sequestered autoantigens could become targets of autoimmune attack – eg. multiple sclerosis

24
Q

What are different immunologically privileged sites?

A
  • Brain
  • Eye
  • Testis
  • Uterus (fetus)

*These organs doo not have antigen cells in them and peptides from these organs are not presented in the thymus so they would be recognized as non-self

25
Q

What is sypathetic ophthalmia?

A

It is an example where ignorance is maintained only until there is damage to an immunologically privileged site

  1. Trauma to 1 eye result in the release of sequestered intraocular protein antigens
  2. Released intraoccular antigen is carried to lymph nodes and activates T cells
  3. Effector T cells return via bloodstream and encounter antigen in both eyes

*If not treated, both eyes will be damaged → complete loss of vision

26
Q

What is autoimmunity the result of?
What factors are involved?

A

It is the result of a combination of multiple factors coming together.

  1. Genetic susceptibility
  2. Environmental triggers such as infections
  3. Breakdown in neural tolerance mechanisms

*Does not occur as the result of only 1 factor

27
Q

Where is multiple sclerosis mostly present world-wide?

A

High prevalence in Canada and North of the US + Northern Europe

28
Q

What are 2 ways in which Autoimmunity is multifactorial?

A
  1. Takes multiple factors to trigger it (genetic + environmental)
  2. Although some autoimmune diseases have traditionally been thought to be mediated by B cells or T cells, it is important to consider that all aspects of the immune system have a role to play.
29
Q

How is the full immune system involved in autoimmunity although it is only caused by an imbalance in the adaptative immune response?
Give an example.

A

Ex: Systemic Lupus Erythematosus

Type 1 IFN plays a critical role…

Genetic susceptibility:
1. Antigen presentation (HLA-DR)
2. IFN/TLR signaling
3. TNF/NF-kB signaling
4. T cell signaling
5. B cell signaling
6. Immune complex clearance
etc.

Envrionmental/endogenous triggers lead to DCs releasing more IFN-a → monocytes, autoreactive Cd4 T cells, autoreactive CD8 T cells, B cells, etc.
- TLR receptors recognize it
- Plaque formation through Ab-Ag complexes
etc.

30
Q

What are the 2 main classifications of autoimmune diseases?
*For clinical purposes

A
  1. Organ-specific autoimmune diseases
    - Type 1 diabetes mellitus
    - Goodpasture’s syndrome
    - Multiple sclerosis
    - Graves’ disease
  2. Systemic autoimmune diseases
    - Rheumatoid arthritis
    - Scleroderma
    - SLE

In systemicautoimmune diseases multiple organs are affected and have a tendency to become chronic, because the autoantigens cannot be cleared from the body.

31
Q

What characterizes type 1 diabetes as an autoimmune disease?

A

Specific destruction of the β-cell producing insulin in the pancreatic islets of Langerhans.
- Other cells in the islets are not destroyed

Studies in the NOD mouse model of type I diabetes have shown that peptides from insulin itself are recognized by the CD8 T cells (Tc).
- These studies confirm that insulin is the autoantigen.

*Glucagon and somatostatin are still produced by alpha and delta cells, but no insulin can be made

32
Q

What characterizes multiple sclerosis as an autoimmune disease?

A

Multiple sclerosis is an example of a T-cell mediated chronic neurological disease that is caused by the destructive immune response against several brain Ags like:
- myelin basic protein
- proteolipid protein
- myelin oligodendrocyte glycoprotein

  1. Unkown trugger sets up initial focus of inflammation in brain and blood-brain barrier becomes locally permeable to leukocytes and blood proteins
  2. T cells specific for CNS antigen and activated is peripheral lymphoid tissues reencounter antigen presented on microglia or DC in brain
  3. Inflammatory reaction in brain due to mast-cell activation, complement activation, Abs and cytokines
  4. Demyelination of neurons
33
Q

Which cells are specifically involved in MS response?

A

Th1/Th17 CD4+ T cells

34
Q

What characterizes rheumatoid arthritis as an autoimmune disease?

A

Rheumatoid arthritis is a chronic disease characterized by inflammation of the synovium (thin lining of a joint).
- As the disease progresses, the inflamed synovium invades and damages the cartilage followed by erosion of the bone.
- Patients suffer from chronic pain, loss of function and disability.
- Matrix metalloproteinases (MMPs) → attacks tissues which activates bone-destroying osteoclasts resulting in joint destruction