T CELL antigen recognition Flashcards
characteristics of t cells that are like b cells
They are lymphocytes
Arise in the bone marrow
Have highly diverse Ag receptors on their surface
Formed from gene rearrangement
Only a single species of receptor exists on any one cell (clonality)
characteristics of t cells that are different to b cells
They mature in the thymus (T cell school)
They recognise different Ag
-Not whole proteins
-Must be processed peptides (key epitopes)
-Presented in complex with MHC molecules
-Requires interaction with Antigen Presenting Cells (APCs)
They never release a soluble Ag receptor
Their receptor doesn’t change on Ag recognition
when is TCR fixed
TCR repertoire is in place by around puberty
Thymic involution
The T cell compartment changes as we age due to repeated exposure to antigens
why is Fixed TCRs are a problem as we age
As we age and are exposed to a variety of antigens, memory T cells begin to accumulate and there is limited space for naïve T cells. When we are born, we have many naïve T cell clones, each expressing a unique T cell receptor. By old age, there are very few naïve cells, and the T cell compartment is full of memory cells. This represents constriction of the TCR repertoire, such that we might not be able to fight off a new infection
The T Cell Receptor (TCR) structure
Heterodimer is composed of an alpha chain and a beta chain. membrane-bound glycoprotein. The variable (V) region contains the antigen binding site, which has hypervariable loops. Structural and sequence diversity here defines which antigen the TCR will recognise. Constant less diverse than the V region. Variability here alters the structure of the TCR such no longer forms a functional antigen-binding site
EXPLAIN gene rearrangement in TCR
Gene segments recombine for each chain
TCR gene rearrangement occurs before antigen exposure
TCRs do not change in response to antigen
