Week 6 Flashcards
What is an autoimmune response?
A response directed against self-antigens that causes tissue damage or altered physiological function resulting from the autoimmune response.
What is attacked in terms of an autoimmune disease?
Usually the host proteins but can be nucleic acids.
What is self tolerance?
The bodies protective mechanism that prevents the development of autoimmune diseases.
In self tolerance, describe gene rearrangement.
Random
What does the random rearrangement of genes in self tolerance lead to?
Generation of lymphocytes that are specific for self-antigens.
What happens to self-reactive T and B cells during self tolerance?
They are destroyed or down-regulated.
Where does central tolerance occur?
Thymus (T cells) or Bone Marrow (B cells)
What is the mechanism of central self tolerance?
Clonal deletion
What is the site of peripheral self tolerance?
Everywhere in the body.
What is the mechanism for peripheral self tolerance?
Anergy, cell death or immune deviation.
Where do T cells originate and develop?
Originate in the bone marrow but develop in the Thymus.
In central self tolerance, what is the first step?
Antigen presenting cells present self-peptides to T cells and the cells can then undergo selection or apoptosis.
In central self tolerance, which cells survive positive selection?
Only the cells whose receptors interactions with self-MHC and self-peptide low affinity survive.
In central self tolerance, what happens in negative selection?
Cells that bind with high affinity to the self-MHC and peptide are deleted.
In central self tolerance, what cells undergo apoptosis?
Cells that fail to interact with self MHC and peptide.
What may happen to some self-reactive T cells that encounter self antigens during central self tolerance?
Some self-reactive T cells that encounter self-antigens in the Thymus develop into T regulatory cells followed by B cell initiated changes in receptors in the bone marrow.
Why is T cell tolerance often regarded as more important than B cell tolerance?
CD4 T cells have a central role in controlling nearly all immune responses. Whereas most B cells will not be able to produce autoantibodies unless the receive appropriate T cell help.
What happens to B cells in the bone marrow, whose receptors are cross-linked by self-antigens?
They are deleted or become self-tolerant.
What happens to T cell’s that do not have any T cell receptors expressed during self tolerance?
Cellular death
What happens to T cells which have T cell receptors with no recognition of self MHC during self tolerance?
Death by default
What happens to T cells which have T cell receptors with strong recognition of self MHC in self tolerance?
Negative selection (signalled death).
What happens to T cells which have T cell receptors with weak recognition of self MHC in self tolerance.
Positive selection
What happens to T cells if they are positively selected for during self tolerance?
Survival and maturation
What are the processes that can occur to peripheral auto reactive cells in peripheral self tolerance?
Clonal detection
Clonal anergy
Regulation and supression
What may cause clonal deletion of self-reactive cells in peripheral self-tolerance?
Physical elimination or apoptosis of cells.
What may cause clonal anergy of self-reactive cells in peripheral self tolerance ?
Lack of co-stimulation or low affinity antigen binding leads to cells not being activated. This is achieved through signalling blocks and/ or inhibitory receptors.
What is immune privilege in terms of peripheral tolerance?
Limited lymphatic drainage, low levels of MHC class I expressed and expression of fasL to kill infiltrating T cells.
Why may expression of fasL cause immune privelledge?
This kills infiltrating T cells and protects the eyes and such like.
How do B cells become anergic during peripheral self tolerance?
When exposed to large amounts of soluble antigen, they down regulate their surface IgM and become anergic.
What is meant by the term anergic?
Lack of immune reaction to antigens.
How do B cells carry out apoptosis during peripheral self-tolerance?
B cells up-regulate the Fasomolecules on their surface and then interact with Fas-ligans-bearing cells resulting in apoptosis.
What happens to B cells which bind to large amounts of soluble antigen with low affinity binding?
They become activated to re-expresses RAG-1 and RAG-2 genes. These genes cause them to undergo DNA recombination and change their antigen specificity.
What are the steps of autoimmunity?
Susceptibility phase
Initiation phase
Propagation Phase
Regulation / Resolution phase
When does the susceptibility phase occur in autoimmunity and what happens during this phase?
Before disease
One or several preconditions for later initiation are satisfied. These tend to be genetic factors or altered immune signalling thresholds that cause disease.
What influences the susceptibility phase of autoimmunity?
Genetic factors that impair regulation and human leukocyte antigen associations.
When does the initiation phase of autoimmunity begin and what indicates its onset?
Begins before the onset of clinical disease and is marked by the presence of an autoimmune response.
What happens (in general) in the initiation phase of autoimmunity?
Hidden epitopes are revealed and new epitopes are created.
What are the possible mechanisms of the initiation phase of autoimmunity?
Post-translational modification.
Proteolytic cleavage of intracellular antigens during cell death and mutation.
Truncations.
Splicings.
What molecular mimicry is used in the initiation phase of autoimmunity?
Pro-inflammatory signals with infection can activate low-affinity, self-reactive T and B cells.
What marks the onset of the propagation phase of autoimmunity?
The propagation of specific immune responses.
What often initiates the propagation phase of autoimmunity?
Tissue damage provides a further drive in the autoimmune response.
What happens during the resolution/regulation phase of autoimmunity?
Immunoregulatory pathways are activated activated, potentially resulting in a natural inhibition or resolution of the clinical disease.
What are the 2 different categories of autoimmune disease?
Organ specific
Non-organ specific
What methods are often used to detect autoantibodies?
Immunofluorescence Radioimmunoassay ELISA Immunoblot Multiplex Immunoprecipitation reactions
What are the types of immunoprecipitation reaction?
Agglutination
Double immunodiffusion (DID)
Counterimmunoelectrophoresis (CIE)
What can be used as antigens in lab tests for autoantibodies ?
Cells
Tissues
Purified native or recombinant antigens.
How are cells prepared for antigen testing in terms of testing for autoantibodies?
Cells are extracted via chemical or mechanical extraction.
Chemical: Extracted using a lysis buffer that can preserve or destroy the protein structure.
Mechanical: Extraction by homogenisation or freeze thaw cycles.
How are tissues prepared for antigen testing in terms of testing for autoantibodies?
And how are they analysed for antibodies?
They are frozen or embedded in paraffin and analysed with monoclonal antibodies using patient serum to determine if they have antibodies.
How are native or recombinant antigens prepared for antigen testing in terms of testing for autoantibodies?
They are coated to plates, beds, magnetic particles, micro spheres or micro spots and then purified.
Why must native or recombinant antigens be purified to be used in lab tests?
This is crucial to maintaining conformational epitopes, tertiary and quaternary structure and post translational modifications.
Also increases the sensitivity and specificity of antibody tests.
What is a qualitative result?
Has a positive or negative result.
What is a semiquantitative result?
Dilutions or titres (e.g. 1 in 40)
What is a quantitative result?
Numerical value
What is hybridoma in terms of antisera?
A single clone of B cells are fused with myeloma cells which immortalises them.
What is polyclonal antisera purified by?
Anitbodies
What is monoclonal antisera purified by?
Hybridoma procedure
What are the advantages and disadvantages of polyclonal antisera being used in immunoassays?
+ Cheap, quick production
- Low reproducibility
What are the advantages and disadvantages of monoclonal antisera being used in immunoassays?
+ Reproducible, specific properties
- Expensive, slow production
Name some qualitative assays for antigen/antibody reaction
Immunoprecipitation
Immunodiffusion
Counter-
Immunoelectrophoresis
Immunofluorescence Microscopy