T-cell receptor complex. The T-cell receptor is associated with six CD3 molecules: a CD3-γ–CD3-ε heterodimer, a CD3-δ–CD3-γ heterodimer, and two chains of CD3-ζ. Single ITAM sequences are present in the cytoplasmic domains of CD3-γ, CD3-δ, and CD3-ε, whereas three such sequences are found in each CD3-ζ chain.