Autoimmunity Flashcards
why are women more likely to have an autoimmune disease
a larger number of genes originate from the X chromosome creating a far greater possibility of mutations occurring - women have two X chromosomes where males have one.
higher levels of female hormones and lower male ones may contribute
what causes autoimmunity
an inability to recognise self from non self (the antigens and molecules presenting them) - when tolerance to self breaks
Bacteria, viruses, toxins, and some drugs may play a role in triggering an autoimmune process in someone who already has a genetic (inherited) predisposition to develop such a disorder.
autoimmune diseases occur when…
- the usual control process are interrupted, allowing lymphocytes to avoid suppression
- when there is an ‘alteration’ in cells/tissue so that it is no longer recognized as “self” and is thus attacked.
what is tolerance?
• Tolerance is the prevention of an immune response against a particular antigen. For instance, the immune system is generally tolerant of self-antigens, so it does not usually attack the body’s own cells, tissues, and organs. Also recognition of MHC cells
what cells do t cells specifically eliminate/bind to (different from b cells)
t cells only eliminate viral infected cells, not free virus or antigens
what did Peter C Doherty and Rolf M Zinkernagel win the Nobel Prize in 1996
for their discoveries concerning “the specificity of the cell mediated immune defence”.
T cells have to interact with MHC molecules and peptides
what are the two types of tolerance
central and peripheral tolerance
what two types of molecules are recognised in t cell activation (autoimmunity)
self MHC + foreign antigen
what is central tolerance
When T cell mature in the thymus, they are checked for their reactivity against self. T cells which react against self are destroyed.
what is positive selection
- occurs when double positive T cells bind cortical epithelial cells expressing Class I or Class II MHC plus self-peptides with a high enough affinity to get the survival signal. (but not too high) (death to those who do not interact with MHC molecules)
what is negative selection of t cells
- occurs when the TCR of a thymocyte engages a peptide–MHC ligand with very high affinity, leading to the apoptotic death of the cell
Deletes potentially self-reactive thymocytes (any cells with high affinity for self), thereby generating a repertoire of peripheral t sells that is largely self-tolerant
T cells with low affinity for self are allowed to maturate
what occurs to T cells that have an intermediate affinity for self
-> upregulation of transcription factor foxp3 turning them into T regulatory cells
these Treg cells suppress reaction to self antigens (cells activated in the periphery)
what is peripheral tolerance
- deletion or anergy of lymphocytes that recognize self antigens in peripheral tissue
T cells in the circulation must receive signals from normal cellular tissue to survive. When this control system fails, the immune system can react against our own molecules
what may cause anergy or inactivation of t cells in the periphery
Lack of accessory signals in presence of TCR engagement with MHC-peptide may lead to anergy or inactivation. -If presentation without co-stimulation
what is a t regulatory response/ what causes it?
T regulatory cells will respond to Ag (antigen) but induce an inhibitory response (regulation) (suppressive activity, no activate)
