T-cell priming Flashcards
What could be a reason for individuals showing immune reactivity to SARS-CoV-2 before being infected by the virus itself?
Individuals who have been infected with other sorts of common cold coronaviruses (CCC) are more reactive to the coronavirus.
What is the concept of immune cross-reactivity based on?
It is based on the concept that there are pre-existing memory T-cells that can react to a new pathogen.
These pre-existing memory cells may have been made when an individual was infected with a different, homologous, pathogen.
Where are naive T-cells activated and by what?
CD4+ and CD8+ are activated in the secondary lymphoid organs by dendritic cells.
What is another name for CD80 and 86?
B7.1 and B7.2 respectively.
How many cells respond, when a dendritic cell presents an antigen?
Roughly 1 in 100 000
What receptors and molecules are involved in which of the 3 steps of T-cell activation?
Signal 1: MHC loaded with antigen binds to TCR.
Signal 2: Co-stimulation between CD80/86 (B7.1/B7.2) on the dendritic cell and CD28 on the T-cell
Signal 3: Cytokines released by the dendritic cell determine effector cell subset
Name five examples of T-helper subsets and the cytokines which lead to their induction.
- Th1 : IL-12 and INF-y
- Th2 : IL-4
- Th17 : IL-6, TGF-b and IL-23
- Tfh : IL-6. IL-21
5 Treg : TGF-b
What is the function of CD40L and CD40?
CD4+ T-helper cells activate CD8+ and B-cells. They do so through CD40L (on the Th cell) and CD40 (on B-cells and CD8+) mediated activation.
What are CD62L and CCR7 characteristics of?
Naive T-cells and some memory T-cells
Which molecules are both important for entering the lymph nodes?
CCL19 and CCL21
What are the characteristics of Central Memory T-cells?
- L-selectin (CD62L) positive
- CCR7-positive
- Circulate the lymphoid organs
- Stem-cells-like, can be activated by antigen and cytokines
What are the characteristics of Effector memory T-cells?
- L-selectin (CD62L) negatice
- CCR7-negative
- Circulate lymphoid and non-lymphoid tissues
- Already differentiated and have high levels of effector molecules
What is the role of Resident Memory T-cells?
They are found only in tissues and are responsible for the response to local infections.
What are the CD8 and CD4 receptors on T-cells doing?
CD8 and CD4 are both co-receptors of TCR. CD8 is on cytotoxic T-cells and CD4 is on T-helpers.
What cells can present extracellular antigen on their MHC-I?
Dendritic cells.
What is cross-presentation important for?
It is important for inducting a viral and tumor immune response.
How many MHC-I/II variants are out there?
3 MHC-I and 3 MHC-II
What part of the MHC molecule is the most affected in terms of polymorphism?
The peptide groove
What is the main difference between different MHC forms?
Each MHC can then bind different peptide sets.
What techniques can be used to study the proliferation of T-cells?
- CFSE / CTV dilution
What techniques can be used to study the proliferation of T-cells?
- CFSE / CTV dilution
- 3H-thymidine incorporation
- Ki67 staining (not used much anymore)
What is the concept of CFSE/CTV (cell trace violet) dilution?
Cells stained with the dye inherit 50% of the staining intensity. By measuring the stain color intensity, one could measure how many divisions/generations of cells have happened.
How can one measure cytokine production in T-cells?
- ELISA
- Elispot
- Intracellular cytokine staining
Briefly explain how Elispot works.
Elispot is a measuring method in which a well is coated with cytokine-specific antibodies. T-cells are then thrown into the well and they release cytokines. The cytokines then form precipitates which are visible as dots.
Quantification of T-cells that produce a specific cytokine is based on the number of dots produced after stimulation.
Briefly explain how Intracellular cytokine staining works.
Activated T-cells are blocked from releasing cytokines, thus those accumulate in the ER. The cells are then made permeable. Antibodies specific to a specific type of cytokine are used, which bind to cytokines in the lysed ER.
This is used to quantify how many cells produce a specific cytokine, using flow cytometry.
How can polymorphisms of the MHC molecules specifically influence an immune reaction?
Polymorphisms influence the peptide binding groove of the MHC molecule. As a consequence, those will find a different peptide chain from the virus proteome, which means that those MHC molecules may activate a slightly different immune response pathway.
Can you get a CD8+ response without MHC-II?
No, because MHC-II activates CD4+ T-helpers, which in turn stimulate CD8+ cells.
What technique can be used to measure an antigen-specific T-cell response?
MHC/Ag-tetramers
What kind of MHC is the MHC-peptide tetramer made of?
MHC-I
Briefly describe MHC tetramer staining.
Four recombinant MHC-I molecules are loaded with a specific peptide and are then bound to streptavidin (carrier molecule). The MHCs then bind to T-cells which express their respective receptors. Amount of cells that react is then counted using flow cytometry.
Why is an MHC-I tetramer needed and not a monomer?
Monomers may have a low affinity to the TCR and thus antigen-specific T-cells cannot be detected.
Does a vaccine or infection lead to the highest immunological memory?
A hybrid between infection and vaccination leads to the highest immunological memory.
What kind of T-cells correlates with milder COVID-19 cases in patients?
CD8+ T-cells that can recognize conserved coronavirus epitopes.
The conserved epitopes may stay the same between all coronaviruses, so CD8+ T-cells can recognize those, even if a patient has never had COVID-19 before.
What kind of T-cells correlates with milder COVID-19 cases in patients?
CD8+ T-cells that can recognize conserved coronavirus epitopes.
The conserved epitopes may stay the same between all coronaviruses, so CD8+ T-cells can recognize those, even if a patient has never had COVID-19 before.
