Which statement best describes the T-cell receptor for antigen?

Which statement best describes the T-cell receptor for antigen?

• A. It consists of IgM and IgD molecules.
• B. It is the same for all T cells.
• C. It is present in the double-negative stage.
• D. Alpha and beta chains are unique for each antigen.

Answer: (D)

T-cell recognition hinges on a receptor that is a heterodimer of an alpha chain and a beta chain. The variable regions of these chains are created by V(D)J recombination during T-cell development, giving each T cell a unique receptor. That unique alpha–beta pairing determines which peptide–MHC complex the T cell can recognize. In other words, the combination of alpha and beta chains defines the receptor’s specificity for antigen, and this diversity in the two chains underlies the ability of the T-cell repertoire to recognize a vast array of antigens. The same antigen can be recognized by many different T cells, each with its own alpha–beta combination, which is why the overall repertoire is so diverse. The other statements are not accurate: B-cell receptors are IgM/IgD, TCRs are not identical across all T cells, and the TCR is not expressed on the surface at the double-negative stage until later development.

T-cell recognition hinges on a receptor that is a heterodimer of an alpha chain and a beta chain. The variable regions of these chains are created by V(D)J recombination during T-cell development, giving each T cell a unique receptor. That unique alpha–beta pairing determines which peptide–MHC complex the T cell can recognize. In other words, the combination of alpha and beta chains defines the receptor’s specificity for antigen, and this diversity in the two chains underlies the ability of the T-cell repertoire to recognize a vast array of antigens. The same antigen can be recognized by many different T cells, each with its own alpha–beta combination, which is why the overall repertoire is so diverse. The other statements are not accurate: B-cell receptors are IgM/IgD, TCRs are not identical across all T cells, and the TCR is not expressed on the surface at the double-negative stage until later development.