imm 5 Flashcards
What are T cells derived from?
derive from common lymphoid progenitor (in bone marrow) but migrate to the thymus for majority of their development.
Once matured what do T cells do?
They enter the bloodstream and migrate to secondary lymphoid organs
Where does the majority of the maturation of T cells occur?
In the thymus
What do immature T cells acquire in the thymus?
There own specific antigen receptor which will be unique to that T cell
Where do mature naive T cells travel?
They keep recirculating from lymphoid to lymphoid anti, they encounter their complimentary receptor
What happens when a naive T cell encounters is complimentary antigen?
The T cell becomes activated and undergoes the final stage of differentiation to become an effector T cellThese cells proliferate and differentiate into effector cells
What is the function of a T cell?
To recognise and bind to antigens
How to T cells bind and recognise antigens?
Via a specific antigen receptor
What is the T cell receptor made up of?
Consist of 2 polypeptide chains, α and β, linked by a disulphide bond.Similar to a single Fab fragment of antibody, has one antigen binding site.
Which family do T cell receptors being to?
members of the immunoglobulin superfamily
T cells can only recognise antigens when…
it is complexed in an MHC not just on its own
Other than T cell receptors what the molecules do all T cells present?
CD3
What does CD3 complex with?
Our T cell receptors to send signals into the cells
Does CD3 actually bind to antigens?
NO it only recognises when an antigen is bound to the T cell
Which molecule is specific to cytotoxic T cells?
CD8
What is the main function of cytotoxic T cells?
Kill virus infected cells or malignant cells
Which molecule is specific to T helper cells?
CD4
What is the main function of T helper cells?
They increase macrophage function| They provide help to the B cells for antibody production
How are T cell receptors generated?
In a similar process to B cells Uses recombinant activates gene (RAG) proteins to perform V(D)J somatic recombination.Guided by 12/23 RSS rule.
Describe the structure of T cell receptors
2 polypeptide chains, α and β, linked by a disulphide bondA transmembrane regionAmino acid binding siteAntigen binding siteCytoplasmic tails
What does each polypeptide chain in a T cell receptor have?
A variabel region| A constant region
What does the transmembrane region do in a T cell receptor?
Polypeptides are inserted into this region so that they are inserted in to the plasma membrane pf the T cell so that they are expressed on the outside of the T cell
Where is the amino acid binding site found on the T cell receptor?
At the amino terminus end of each polypeptide chain
What makes up the antigen binding site?
Both the polypeptide chains
What does MHC stand for?
Major histocompatibility complex
What do MHCs do?
They bind and present antigens to T cells for inspection via TCR.
What are MHCs made up of?
Transmembrane glycoproteins that are highly polymorphic
What does polymorphism in MHC lead to?
Can lead to transplant graft injection| This is why we need to do a tissue type matching
What type of antigen is presented on an MHC?
Both intra cellular and extracellular antigens are processed and presented at the cell membrane for inspection within MHC
How many CLASS of MHC do we have?
2:MHC class I MHC class II
What does MHC I do?
binds and presents intracellular derived antigen (eg malignant cells)
Which of the types of MHC is carried out by the majority of nucleated cells?
MHC I
Which cell is MHC I not present in?
Red blood cells
Is the process carried out by MHC I specific?
NO all types of proteins are presented by the MHC I molecules It will present everything both self and non self proteins
Why is it important that all cells can perform MHC I presentation?
As all of our cells can be infected by viruses
Where are viral proteins made?
Within a cell but the stuff they produce is no self| So the antigen is intracellular
Other than viruses what other reason can cells be presenting a non self intracellular antigen?
Mutated tumour antigens
What does MHC class II do?
binds and presents extracellular derived antigen.
Which cells can carry out MHC II presentation?
ONLY Carried out by professional Antigen presenting cells (APC).
What do MHC II bind to?
Binds to bacteria or their products that have then been ingested and presents these antigens
What are the differences in the structure of MHC class I and MHC class II
MHC class I is made up of a one long alpha chain and a smaller beta chain Only the alpha chain contributes to the antigen biding grooveMHC II is made up of one alpha and beta chain both similar sizes Both alpha and beta contribute to the antigen binding groove
What are the similarities in the structure of MHC class I and MHC class II
Both have a peptide binding groove| Both are composed of 2 polypeptide chains
On which cells are MHC class I proteins present
All somatic cells
On which cells are MHC class II proteins present
Dendritic cells B cells Macrophages
For MHC I what sized residues will fit into the antigen binding site?
8-10 residues
For MHC II what sized residues will fit into the antigen binding site?
13 residues.