Flashcards in T lymphocyte and antigen recognition Deck (25)
What is the general structure of a T Cell Receptor?
It consists of an alpha and beta chain
Both chains have a variable region and a constant region
What other receptor are TCRs associated with and how does it transmit signals?
CD3 is present on all T lymphocytes and they have a longer cytoplasmic tail than the TCR
Signals from the TCR are transmitted to the internal compartment of the cell via the CD3 receptors
The tails of CD3 have tyrosine residues
When antigen binds to the TCR, phosphorylation of tyrosine occurs in the tails, which leads to many chemical cascades.
What class of MHC do CD4+ T cells bind to?
MHC Class II
What class of MHC do CD8+ T cells bind to?
MHC Class I
What type of cells are CD4+ T cells? What do they do?
T helper cells – T helper 1 cells are involved in inflammatory responses (activate macrophages) whereas T helper 2 cells are involved in B cell activation
What type of cells are CD8+ T cells? What do they do?
Cytotoxic T lymphocytes – kills virus infected cells
Where are immature thymocytes found in the thymus?
In the cortex – mature thymocytes are found in the medulla
Describe, in full, T cell development in the thymus.
T cells initially have no TCR or CD4/CD8 receptors
The beta chain of the TCR assembles first followed by the alpha chain
If the TCR is functional, the T cell goes on to express both CD4 and CD8 receptors
Depending on which MHC class it binds to it eventually ends up being only CD4+ or CD8+
What do CD4 and CD8 bind to?
They bind to the side of the MHC molecule
In what order does gene rearrangement take place?
Beta chain is rearranged first (VDJ recombination) and then the alpha chain (VJ recombination)
What percentage of thymocytes survive selection?
Describe, in full, the structure of MHC Class I.
MHC Class I consists of a heavy alpha chain which is polymorphic and a beta-2 microglobulin chain which is the same in everyone
Only the alpha chain has a transmembrane domain
How does the light polypeptide associate to the heavy polypeptide in MHC Class I?
What part of MHC Class I is transmembrane?
Describe, in full, the structure of MHC Class II.
MHC Class II consists of two polypeptides of a similar size, an alpha and a beta chain
Both chains have a transmembrane domain
What part of MHC Class II is transmembrane?
Both the alpha and beta chains have transmembrane domains
What is the difference between the types of peptides presented by Class I and Class II?
Class I presents peptides that are smaller than the MHC molecule
Class II presents peptides that are longer than the MHC molecule so it often has bits protruding out of the MHC molecule
Describe how the structure of MHC allows it to bind to a broad variety of peptides.
It has a binding motif that consists of binding pockets where you get particular amino acids binding in those positions – this is a feature that is conserved in most peptides
What is the name for the Human MHC region in the genome?
Human Leukocyte Antigen
What are the types of MHC Class I genes?
A, B and C
What are the types of MHC Class II genes?
DP, DQ, DR
How many types of MHC molecule can one person produce?
12 – 6 class I and 6 class II
What is an MHC haplotype?
Group of MHC alleles linked together on a single chromosome
Describe the process of antigen presentation via MHC Class I.
MHC Class I present endogenous antigens
Viral proteins are processed by a proteasome and move through TAP protein into the ER
In the ER, the MHC Class I molecule assembles and a chaperone protein aids its folding
Once it has fully assembled, it can move to the cell surface via the golgi apparatus