Adaptive immune responses: T cells Flashcards
What is the difference between B and T cells when it comes to their specialisation?
B cells stay and specialise in the bone marrow
T cells migrate to the thymus in order to specialise
Where is the thymus located?
In the thoracic cavity
Next to the heart
Why is the thymus especially important in children?
Most T cells develop during childhood
Why are TCRs and BCRs specific?
Operate through a lock and key model
Why is clonal expansion important?
The population of T cells with a specific TCR is low
Cells which are useful in fighting the microbes are expanded
This clonal expansion forms T cells with the same TCR which is relevant to the infection
What is one reason why adaptive immunity takes longer than innate immunity?
The T cells with the specific TCR to the antigen have to clonally expand
What are the 4 features of the adaptive immunity?
Specificity
Diversity
Memory
Clonal expansion
What is the functional significance of the adaptive immune system being specific?
Ensures that distinct antigens elicit specific responses
What is the functional significance of the adaptive immune system being diverse?
Enables the immune system to respond to a large variety of antigens
What is the functional significance of the adaptive immune system having memory?
Leads to enhanced immune response to repeated exposures to the same antigens
What is the functional significance of the adaptive immune system clonally expanding?
Increases the small number of antigen-specific lymphocytes from a small number of naive lymphocytes
What percentage of T cells express TCRab?
90%
What are the T cells which express TCRab split into?
CD4 cells
CD8 cells
What do T cells which don’t have TCRab express instead?
TCRyd (gamma, delta)
Why does the T cell receptor need a CD3 complex?
The TCR is not embedded in the T cell membrane deeply enough to transduce a signal to the cell
T CD3 molecules therefore do the signalling for the TCR
What is CD3?
Complex of invariant chains which allows for the TCR signal to be transduced into the cell following binding with antigens
Is the CD3 signal enough for a response to be evoked upon binding with antigens?
No
Requires another costimulatory receptor
The most important is CD28
What is signal 1?
CD3 intracellular pathway activation
What is signal 2?
CD28 intracellular pathway activation
What happens to the T cell if it just receives signal 1?
Does not become activated
Becomes anergic
How does the T cell become activated?
Through obtaining both signal 1 and signal 2
What is required for the costimulatory receptors on T cells to become activated?
APCs need to have ligands for costimulation
These form the B7 complex
What forms the B7 complex?
CD80 and CD86
What does the nature of the immune response depend on?
The type of T cell which is activated
Which cells do CD8 T cells kill?
Infected cells
Cancer cells
Which MHC molecule do CD8 T cells interact with?
MHC I
Through which mechanisms do CD8 T cells kill their targets?
Cytotoxic granules containing perforin and granzyme
Binding to death receptors on target cells like Fas
Describe how CD8 T cells kill their targets through granzymes
Perforin form pores which facilitate the entry of granzymes
Granzymes cause apoptosis and cell death
Describe how CD8 T cells kill their targets through death receptors
CTL can bind to death receptors on target cells
Including death receptor FasL
Upregulation of the ligand on CD8 T cells will kill the cell expressing FasR
Describe the different types of CD4 T cells
Helper cells
Regulatory cells
What is the role of CD4 regulatory T cells?
Inhibitory
Play an important role in autoimmunity
Suppress immune responses
What are 3 different subclasses of T helper cells
Th1
Th2
Th17
What is the marker for Th1 cells?
IFN y
What is the target cell for IFNy?
Macrophages
What type of pathogen do Th1 cells respond to?
Intracellular pathogens
What are the markers for Th2 cells?
IL-4
Il-5
IL-13
What is the target cell for Th2 cells?
Eosinophils
Which pathogen do Th2 cells respond to?
Parasites
What are the markers for Th17 cells?
IL-17
IL-22
What is the target cell for Th17 cells?
Neutrophils
Which pathogens do Th17 cells respond to?
Extracellular pathogens
How do the cells of the immune system travel around in the body?
Blood
Lymph vessels
How are the collections of cells in the lymph nodes connected?
Through lymphatics
Apart from clonal expansion, what is another way T cells compensate for the low population of T cells with specific receptors?
Travel throughout the body to find microbes
Can T cells respond to antigen straight away like B cells?
No
They need an antigen presentation stage
This is why the humoral immune response comes before the cellular immune response
What is another name for the immune system under the control of T cells?
Cellular immune response
