The T-cell receptor signaling complex & CD3 complex

Why can't T-cell receptor proteins initiate intracellular signaling on their own?

T-cell receptor proteins lack a significant cytoplasmic domain, so they cannot initiate intracellular signaling events on their own.

What must the T-cell receptor interact with to initiate signaling?

The T-cell receptor must interact with other cell-surface molecules, including the CD4 or CD8 coreceptor and the CD3 complex, to initiate signaling.

What is the CD3 complex composed of?

composed of the δ, ε, and γ chains and two ζ chains. These polypeptides recruit signaling molecules activated upon TCR engagement.

What is the role of CD28 in T-cell activation?

Provides an essential costimulatory signal for naïve T-cell activation.

How does CTLA4 affect T-cell activation?

CTLA4 binds to the same molecule as CD28 and downregulates T-cell activation, preventing unchecked T-cell activation and effector functions.