Transcript Cloning of the TCR b-chain gene by subtractive hybridization

Self-MHC restriction of the T cell receptor
Self-MHC restriction of TC cells
R. Zinkernagel & P. Doherty
Cloning of the TCR b-chain gene by subtractive hybridization
By S. M. Hedrick &
M. M. Davis
3 important assumptions made by Hedrick and Davis:
• The TCR mRNA would be associated with membranebound polyribosomes like the mRNAs that encode
other integral membrane proteins. (eliminate ~97%
mRNAs)
• 98% of the genes expressed in lymphocytes are
common to B and T cells. TCR should be in the 2%
genes expressed specifically in T cells. (DNA subtractive
hybridyzation eliminates 98%)
• TCR genes should undergo DNA rearrangements like
those observed in the Ig genes of B cells.
Structure of the ab T-cell receptor and surface IgM
Difference in the structures of the ab and gd receptors
Limited diversity
Organization of mouse TCR gene segments
A productive rearrangement of the a chain gene segments deletes Cd
TCR variable- region genes rearrange in a manner similar to Ig gene
Junctional diversity
The CDR3 of the TCR has greater diversity than
that seen in immunoglobulins
T-Cell Receptor Complex: TCR-CD3
or ζη
CD3 is required for membrane expression of T cell receptors
Structures of the CD4 and CD8 coreceptors
or aa dimer
CD8 binds to class I by contacting MHC class I a2 and a3 domains
CD4 binds to class II through MHC class II a2 and b2 domains
Affinity of TCR for peptide-MHC complexes is
weak compared with antibody binding
T cell-APC interactions are strengthened by cell-adhesion molecules,
including CD2, LFA-1, CD28, and CD45R
Role of coreceptors in TCR binding affinity
The ternary complex
Of mouse TCR
Bound to MHC
Class I and peptide
CDR3
CDR3
MHC molecule viewed from above
not in
contact
with
peptide
CDR regions of mouse TCR a and b chains viewed from above
TCRs interact differently with class I and class II moleucles
 Alloreactivity of T cells: in addition to self-MHC
plus antigens, T cells also respond to foreign MHC
molecules, a reaction that leads to rejection of
allogeneic grafts (transplants in the same species)
 Alloantigens: epitopes present on molecules that
differ among members of the same species
because of genetic variation.
 T cells recognize a foreign MHC molecules
directly. ~1-5% of all T cells are reactive to
alloantigen.