The
TCR complex
• 2 pairs* of α,β
variable chains associate
with the invariable CD3 accessory
chains (2 ε, 1 δ and 1 γ chains).
For maximum signaling, the ζ homodimer
is also required.
• CD3 ε, γ and δ chains consist
of a extracellular Ig-like
domain and a single
intracellular ITAM each, while the
ζ chain contains 3 ITAMs and only a very short extracellular domain.
•The CD3 complex and ζ homodimer associate with the TCR by charge interactions within their transmembrane regions. To balance the charges - 2 TCRs with one CD3 complex and one ζ homodimer, or 5 ITAMs/TCR.
•The greater # of ITAMs/TCR may allow for greater flexibility in signaling.