T-Lymphocytes and Antigen Recognition Flashcards
What type of pathogen do T-Cells combat?
Intracellular, as antibodies can only attack extracellular pathogens
What does the T-cell receptor detect?
Antigen presented on MHC molecule of infected cell
What CD do all T-cells express?
CD3
What do CD4 receptors do?
Recognise antigens on MHC class II
What cells have CD4 receptors?
T helper cells
What do CD8 receptors do?
Recognise antigens on MHC class I molecules
What cells express CD8 receptors?
Cytotoxic T lymphocytes
What do CD3 molecules do, and what are they a part of?
Deliver signal to T-cell once antigen has been recognised.
Part of the T cell receptor (TCR)
What do CD4 cells do?
Secret cytokines to recruit effector cells and activate macrophages
What do CD8 cells do?
Are cytotoxic and kill target cells by secreting cytokines to induce apoptosis
What receptors do T-cells have when they arrive at the thymus (immature)
CD4-
CD8-
TCR-
When the TCR has been developed, what receptors are present on a T cell?
CD4+
CD8+
TCR+
How is a CD co-receptor removed?
By exposure of T-cell to MHC class I/II, determining the CD to be removed.
What percentage of T-cells survive selection?
5%
What does the Major Histocompatibility complex do?
Display sample of internal cell components for immune recognition.
Markers of self/health; continuously present
What are the 4 regions of MHC molecules?
Cytoplasmic
Transmembrane
Immunoglobulin like
Peptide binding
What size Peptides do each MHC class present?
MHC Class I: 8-10 amino acids
MHC Class II: >13 amino acids
What chains does an MHC Class I molecule have?
Alpha 1 Alpha 2
Beta 2 Alpha 3
(Beta 2 is microglobulin)
What chains does an MHC Class II molecule have?
Alpha 1 Beta 1
Alpha 2 Beta 2
What are the differences between MHC Classes I/II?
Class II has 2 cytoplasmic regions
Polypeptide chains are the same length in Class II
Which cells express MHC Class I?
All nucleated cells.
Levels may fluctuate during infection or by cytokines
Which cells express MHC Class II?
Professional antigen presenting cells
What are endogenous antigens?
Antigens that come from inside cells - use CD8 Class I restricted T-cells
What are Exogenous antigens?
Antigens from outside cells (e.g. phagocytotic and presented antigens) - Use CD4 Class II restricted T-cells
What are effector T cells?
Cells that have encountered antigen, proliferated and differentiated into cells that participate in host defence
What happens to the effector pool after an infection is cleared?
Effector pool contracts to memory pool, as cells die if not signalled to stay alive
What are MHC’s called in humans, and where on the genome are they coded for?
Human Leukocyte Antigen
Chromosome 6
What gene with relation to the immune system is regarded as the most polymorphic?
MHC gene
Over 4200 HLA alleles
What is the main antigen presenting cell?
Dendritic cell
What is the 3 signal licensing model?
- Antigen recognition - T-cell activation
- Co-stimulation - surface molecules on Dendritic cells need to enter TCR to activate
- Cytokines - produced by D cells activate T cells
What is the function of CD8 Cytotoxic T-cells?
To kill infected cells by recognising MHC I peptide
What are the 2 ways a Cytotoxic T-cell can kill?
- Perforin molecules polymerise to form pores to allow granzymes to be injected into cell to drive apoptosis
- Fas ligands interact with target cell Fas receptors to induce cell death
Why are Cytotoxic T-cells described as serial killers?
As they won’t stop at one cell, they’ll kill as many as they can
What happens to granules in a CD8 T-cell when a pathogen is detected?
They polarise towards the pathogen side of the cell
What are the 4 main functions of T helper cells?
Macrophage activation
Delayed type hypersensitivity response
B cell activation
Regulation
What disease is charecterised by a lack of T helper cells?
HIV/AIDs
How are subsets of T helper cells defined?
By the cytokines they release
Name 4 subtypes of T helper cell, and what they do:
T helper 1: Boost intracellular immune response. Activate macrophages
T helper 2: Boost anti-multicellular response. Activate B-cells
Follicular helper T cells: Essential for generation of isotope-switched antibodies
T regulatory cells: Maintain tolerance of self-antigens, regulate activation/effector functions of other T-cells
What do Th17 cells do?
Talk to neutrophils to kill bacteria
What are the two phases of delayed type hypersensitivity?
Sensation phase: Dendritic cell takes up antigen and presents to T-cells. Memory pool built up
Effector phase: Second exposure severe response in macrophage mediated response and mast cell degranulation.
What is different between B cell and T cell memory?
T-cells don’t undergo affinity maturation - Don’t improve over time
What is T-cell exhaustion?
Over time, CD8 pools contracts to prevent excess damage; problomatic in cancer, HIV where infection has not cleared.
