T cells and Antigen Presenting cells Flashcards
There are two major groups of T cells which are they?
- Cytotoxic T-cells
- Th-cells
What does the T cell receptor consist of?
The TCR complex consists of
- α chain and β chain (both together
form the antigen binding site)
- CD3 molecules for signal transduction
Co-receptors:
- T helper cells => CD4 on surface
- cytotoxic T cells => CD8
Somatic recombination of TCR genes increases the diversity of TCRs, what is combinational and junctional diversity?
- Combinatorial diversity: combination of different V(D)J genes to generate diverse α and β-chains
- Junctional diversity: non-template encoded (N) and palindromic (P)
nucleotides are randomly added
between the V-(D-)J sequences
Recognition of antigens by T cells requires antigen-presentation, what is Major histocompatibility complex (MHC)?
They are surface molecules for antigen presentation. MHCs present peptides.
All nucleated cells are APCs and express MHC class I. Other APCs, such as dendritic cells, B-cells, macropahge, MHC class II-expressing cells.
MHC polygenicity, polymorphisms and co-dominant expression of alleles increase…
the diversity of presented
peptides
For antigen processing and presentation, where do the MHC 1 and 2 pathways occur?
MHC class 1 => intercellular antigen
MHC class 2 => extracellular antigen
Activation/priming of naive T cells in lymph nodes requires three signals which?
Signal 1: Recognition of
antigen presented on MHC I
or II
Signal 2: co-stimulation
Signal 3: cytokines pass on
additional information – next
lecture
Name the consequences of T cell activation for CD4 cells and CD8 cells?
- Activation of CD4 cell
→ clonal expansion,
→ polarisation into T helper cell subsets
→ effector phase
→ immune memory - Activation of CD8 cell
→ clonal expansion
→ effector phase (cytotoxicity)
→ immune memory
The effiency of B cell memory is reliant on the number of responses?
After the second (infection) response B cells produce more antibodies, is quicker to react, and there is a higher antibody affinity
What is immunological tolerance?
The state of unresponsiveness to molecules that the immune system could recognize and attack
What are self antigens?
They are peptides that originate from our own body and are continously presented on MHCs. Immunological tolerance is needed to avoid T-cells attacking endgenous tissues
Where and how the does body test that TCR can recognize MHC and peptide combo and that it is not recognized with too high affinity?
(4 outcomes)
Its carried out in the thymus.
If there is no affinity between TCR and MHC the T-cell will not be selected and go through apoptosis
If there is a low affinity between TCR and MHC then its selected. It will have either CD4 or CD8, depending on if it recognized MHC II or I
If the affinity was intermediate the T-cell be selected, however it will become a regulatory T cell (Treg)
If there is a high affinity there will be a negative selection. Apoptosis.
What are the effector functions of cytotoxic T cells CD8+ ? (2 types of killing)
There is perforin/granzyme mediated cell killing and FAS/FAS-L mediated cell killing.
In perforin/granzyme mediated killing, the t-cell binds to the target cell releases perforin and granzyme into the target cell. perforin induces the uptake of granzyme into the endosome. the granzyme => apoptosis of cell
There are 2 ways T helper cells CD4+ contribute to activation of
cytotoxic T cells, which?
- CD4+ helper Tc produces cytokines that stimulates CTL differentiation
- CD4+ helper Tc enchances the ability of APCs to stimulate CTL differentiation
Antibodies can change its affinity maturation, change from membrane to sectreted form, and in isotype switching. Which are Th-cell dependent?
- affinity maturation requires Th-cells
- change from membrane to sectreted form is Th-cell independent
- isotype switching is Th-cell dependent
