Figure 6-9
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.