Autoimmunity Flashcards
What is immunological tolerance?
Immunological tolerance = unresponsiveness to an antigen that is induced by previous exposure to that antigen
The same antigen may induce tolerance or immune response depending on..?
- Conditions of exposure
- Absence of other stimuli
What are tolerogens?
Tolerogens = antigens that induce tolerance
What is self-tolerance?
Self-tolerance = tolerance to self-antigens:
- Failure of this is called autoimmunity, and diseases they cause are autoimmune diseases
What is done by the body to avoid autoimmune disease?
- T and B cells bearing self-reactive molecules must be eliminated
- Achieved by central and peripheral tolerance
What are important organs for central tolerance?
- Thymus
- Eliminates T cells with high affinity to self-antigens
- Bone marrow
- B cell tolerance
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Describe the mechanism of central tolerance?
- Within cortex of thymus, T cell progenitors are tested against antigens
- If they do not react at all they die – death by neglect
- If they have strong recognition for self-antigens they die – negative selection
- If this does not happen they develop further – positive selection
- If low affinity to self-antigens they can develop into Treg cells still
- Cells go into periphery
Where does central tolerance occur for T cells?
Cortex of thymus
Where does central tolerance for B cells occur?
Bone marrow
What is peripheral tolerance?
Safety mechanism encase some reaction cells escape primary tolerance:
- Mature lymphocytes that recognise self-antigens in peripheral tissues become incapable of activation or die by apoptosis
- Can happen due to absence of certain antigens within thymus/bone marrow
What are some of the different mechanisms of peripheral tolerance?
- Anergy (functional unresponsiveness)
- Stimulation without co-stimulation, which is required
- Antigen recognition without co-stimulation
- Treg suppression
- Autoreactive T cells inhibited by Treg cells
- Deletion (cell death)
- Self-antigens hidden from immune system by anatomical barriers
Overcoming peripheral tolerance can result from?
- Inappropriate access of self-antigens
- Inappropriate or increased local expression of co-stimulatory molecules
- Alterations in the ways in which self-molecules are presented to immune system
What increases the risk of overcoming peripheral tolerance?
- Inflammatory or tissue damage
- Due to increased activity of proteolytic enzymes, leading to high concentrations of peptides being presented to responsive T cells
- Infection
- Structure of self-peptides altered by viruses, free radicals or ionising radiation thus bypassing previously established tolerance
How can inflammation or tissue damage allow peripheral tolerance to fail?
- Due to increased activity of proteolytic enzymes, leading to high concentrations of peptides being presented to responsive T cells
How can infection cause peripheral tolerance to fail?
- Structure of self-peptides altered by viruses, free radicals or ionising radiation thus bypassing previously established tolerance