T cells Flashcards
When can T cells recognise protein antigens?
Only after they are broken down into peptide fragments
How are T cells presented with peptides?
the MHC class 1 molecules
What receptors do T cells express on their surface?
- T cell receptor (TCR)
- Either a CD8 or CD4 receptor
Where is MHC class 1 found?
On the surface of most nucleated cells
What type of T cells express the CD8 receptor on their surface?
Cytotoxic T cells
What is the function of CD4 T cells?
They help other innate and adaptive immune cells to execute their effector function (‘helper T cells’)
Which MHC class do CD8 T cells respond to?
Class 1
Which MHC class do CD4 T cells respond to?
Class 2
Where is MHC class II found?
How many chains are T cell receptors made up of?
8
What is the function of the alpha and beta chains of T cell receptors?
They mediate antigen recognition
What are MHCs?
Glycoproteins which display peptides on the surface of T cells
How many gene loci are there for where MHC 1 are expressed?
3
How many different MHC class 1 are on each cell?
6
What type of proteins are processed and presented with MHC class 1 molecules?
Cytosolic proteins
Outline how MHC class 1 presents proteins
- cytosolic proteins are processed to peptides in proteasome
- Peptides bind to MHC class 1 molecules in the ER
- The MHC class 1 molecules are transported through the Golgi apparatus and trafficked to the surface
What are the characteristics of MHC Class 1?
- One heavy chain
- Associated with beta-2 microglobulin
- Peptide short
What type of proteins do MHC Class II molecules present?
Extracellular proteins
Outline how MHC Class II presents proteins
- Proteins are taken into endocytic vesicles
- The proteins are then digested to peptides in the endosomes
- Vesciles containing MHC Class II fuse with the endosomes and then resulting molecules are moved to the surface of the cell
What are the characteristics of MHC Class II?
- 2 heavy chains
- binds longer peptides than class 1
Where are T cells produced?
In the bone marrow
Where are T cells educated?
The thymus
What type of cells activate T cells?
Dendritic cells
How many types of CD4 T cells are there?
3
What are the 3 groups of CD4 T cells?
- Th1
- Th2
- Th17
What is the function of TFH cells?
They enhance B cell differentiation in germinal centres
What are the types of CD4 T cell?
- Helper
- Follicular helper
- Regulatory
What is the main function of CD4 regulatory T cells?
They supress the immune response to prevent inappropriate response to self
What is the function of Th1 cells?
- Help macrophages respond to intravesicular pathogens by producing cytokines
What costimulatory molecules do dendritic cells produce that activate T cells?
CD80 and CD86
What effects does an activated macrophage have?
- Increases production of oxygen radicals
- Increases intracellular killing
- Increases production of cytokines to drive inflammation
- Recruits other immune cells
How can macrophages provide feedback communication?
Peptides from the degradation of bacteria can be presented on MHC class II molecules
How do Th1 and Th2 cells help B cells to produce antibodies?
They stimulate isotype swtching
Explain the role of dual recognition in activation of B cells?
- 2 recgonition events must occur independently in order to activate b cells
- Helps to prevent self-recognition
What recognition events must occur to activate a B cell?
- CD4 T cellhas to recognise an antigenic peptide
- B cell needs engagement of the B cell receptor
How do TFH help activate B cells?
They promote the formation of germinal centres
What is the function of CD8 T cells?
They are cytotoxic T cells which kill tumour cells or cells infected by cytosolic pathogens
What do CD8 T cells secrete as a pro-inflammatory cytokine?
IFNγ
What cytotoxic proteins do CD8 T cells produce?
- Perforin
- Granzymes
- Granulysin
How do CD8 T cells release cytotoxic proteins?
- Recognition of a target cell occurs
- Cytotoxic granules move and become polarised
- The granules are then released at the site of cell contact
