Molecules of cell mediated immunity Flashcards
What lymphocytes are mainly involved in cell mediated immunity
T lymphocytes
How do T cells specifically recognise a antigen
T cell receptor TCR
Part of immunoglobin superfamily but not an immunoglobin and is always membrane bound
How many types of TCR
TCR1 TCR2
Polypeptide chains of TCR1 vs TCR2
TCR2= alpha and beta
TCR1 = delta and gamma
TCR1 structure
- small subset
- below mucosal epithelia and skin
- Good for local immunity in mucosal tissue
- they DO NOT CREATE MEMORY
- They recognise antigen WITHOUT MHC!! (sees phosphorylated metabolites?)
TCR2 is the main surface receptor to recognise antigens
What is its structure
- Alpha and beta chain connected by disulphide bond
- Glycosylated
- Has contant domain and variable domain-varied with diff antigen
- Like antobodies, the varibale domain contains hypervariable region called CDR
- Variable alpha and variable beta =antigen binding site
Why is TCR smaller than antibody
It baso coressponds to a isolated Fragment antigen binding site (FAB)
Antibodies will eventually work in its soluble form from B cells so its Fragment crystallizable serves as an adapter
BUT TCR never secreted so dont need large constant part
How does TCR do signal transduction once it binds with antigen
With TCR complex
Composed of TCR and CD3 and zeta chain (memebrane proteins)
Once TCR bound, CD3 and ƺ
activate cytoplasmic protein kinases.
They in turn activate other proteins
inside the cell, transducing the signal.
What is MHC
Major histocompatibility complex
Cell surface proteins involved in cell mediated immuity
Histocompatibilty= whether transplant rejected or accepted by host
MHC locus
MHC genes are so closely linked that we often talk about “MHC
locus” in singular. In the human, they and their products are
called HLA (i.e. “human leukocyte antigens”). The HLA genes
HLA genes help immune system regognise d=self protein and foreign protein
are located on chromosome 6.
What are the 2 major classes of MHC
MHC1= expressed by all nicleated cells except trophoblasts in placenta (and erthyrocytes obvi no nucleus)
MHC2= mononuclear phagcytes like macrophages and also B cells
Which is more precise MHC1 or MHC2
MHC2 because it can hold more peptide chains
MHC1 made from alpha chain:)
What type of antigens do T Cells recognise and do they bind directly to antigen
They inly recognise PROTEIN antigens
THEY DO NOT RECOGNIZE NATIVE ANTIGEN ON PATHOGEN SO DOESNT BIND TO IT
T cells recognize the antigen only when shown to them by
another cell called antigen-presenting cell (APC).
How does the antigen presenting cell process the antigen to put it on its surface
Incomplete proteolysis and places fragements on surface
T cells only recognise sequential epitopes
(the other is conformational amino acid sequences not next to each other)
What is MHC restriction
T cells WILL NOT recognise APC + MHC from another organism
Therefore the MHC must be SELF MHC from the APC
