Page 398 - Veterinary Immunology, 10th Edition

chains (γ, δ, ε, ζ, and η) arranged as three dimers γ-ε, δ-ε, and
VetBooks.ir either ζ-ζ or ζ-η. The TCR β chain is linked to the γ-ε dimer, and the

TCR α chain is linked to the δ-ε dimer.

FIG. 14.5 Overall structure of the TCR/CD3 complex. The signal
transduction proteins are collectively classified as CD3. About 80%
of α/β TCRs use ζζ dimers. The remaining 20% use ηζ
heterodimers. Most γ/δ TCRs probably use a completely different
signal transduction complex.

CD4 and CD8

Two additional proteins closely associated with the TCR are called
CD4 and CD8. CD4 is a single chain of 55 kDa, and CD8 is a dimer
of 68 kDa. (One chain of CD8 is called α, the other is β. In humans,
pigs, mice, and cats, CD8 is an α-β heterodimer or, less commonly,

an α-α homodimer.) CD4 and CD8 determine the class of MHC
molecule that can be recognized by the T cell (Fig. 14.6). For

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