Chapter 9
T-cell Receptor
Dr. Capers
Kindt • Goldsby • Osborne
Kuby IMMUNOLOGY
Sixth Edition
Chapter 9
T-Cell Receptor
Copyright © 2007 by W. H. Freeman and Company
T cell receptor vs B cell receptor

T cell receptor is only membrane bound
○ Doesn’t appear in soluble form like antibodies
so more difficult to assess it’s structure
Antigen binding of T cell receptor is
weaker than that of antibodies
 Antigen recognized by T cells is not
antigen alone but antigen associated
with MHC molecules




(a) T cell receptor
(TCR) is specific for
peptide A
(b) Right MHC
haplotype but wrong
antigen (peptide B)
(c) Right antigen
(peptide A) but
wrong haplotype

T cell receptor (TCRs)
○ TCR heterodimers are similar to
immunoglobulins
 Therefore they are classified in immunoglobulin
superfamily
 Resembles Fab fragment

TCRs
○ Associate with MHC – αβ TCR
○ Do not associate with MHC – γδ TCR
- Much remains to be learned of function of γδ TCR
Rearrangement of TCR genes

Similar to that of Ig
 Rearrangement of α and γ chains
○ V, J, and C segments
 Rearrangement of β and δ chains
○ V, D, J, and C segments

Generation of TCR diversity (a lot like Ig)
○ Multiple germ-line gene segments
○ Combinatorial V-(D)-J joining
○ Junctional flexibility
○ P-region nucleotide addition
○ N-region nucleotide addition
○ Combinatorial association of light and heavy
chains

However, there is no somatic mutation with
TCR
○ May be to ensure that after thymic selection, the
TCR doesn’t change to cause self-reactive T cell
TCR-CD3 Complex

Accessory
molecules help in
signal
transduction after
interaction of T
cell with antigen
 2 Zeta ζζ chains
 Heterodimer of delta
epsilon γε chains
 Heterodimer of
delta epsilon εδ
chains
T cell accessory molecules

T cells can be divided into 2
populations:
○ CD4+
 Recognize antigen associated with Class
II MHC OR
○ CD8+
 Recognize antigen associated with Class I
MHC
○ CD4 and CD8 function as
coreceptors and assist with signal
transduction

Affinity of TCR for
peptide-MHC
complexes is
enhanced by
coreceptors
Allogenic – genetically different
individuals of same species
 Alloreactivity of T cells is puzzling:

○ Evidence supports that T cells can only
respond to antigen+MHC
○ However, T cells can recognize a foreign MHC
molecule alone
- As with transplants