Describe (A) five ways in which T-cell receptors are similar to immunoglobulins, and (B) five ways in which they are different (other than the way in which they recognize antigen)

Question

What will be an ideal response?

Answer 1

A. Similarities. (1) The T-cell receptor has a similar overall structure to the membrane-bound Fab fragment of immunoglobulin, containing an antigen-binding site, two variable domains, and two constant domains. (2) T-cell receptors and immunoglobulins are both generated through somatic recombination of sets of gene segments. (3) The variable region of the T-cell receptor contains three complementarity-determining regions (CDRs) encoded by the Vα domain and three CDRs encoded by the Vβ domain, analogous to the CDRs encoded by the VH and VL domains. (4) There is huge diversity in the T-cell receptor repertoire and it is generated in the same way as that in the B-cell repertoire (by combination of different gene segments, junctional diversity due to P- and N-nucleotides, and combination of two different chains). (5) T-cell receptors are not expressed at the cell surface by themselves but require association with the CD3 γ, δ, ε, and ζ chains for stabilization and signal transduction, analogous to the Igα and Igβ chains required for immunoglobulin cell-surface expression and signal transduction.
B. Differences. (1) A T-cell receptor has one antigen-binding site; an immunoglobulin has at least two. (2) T-cell receptors are never secreted. (3) T-cell receptors are generated in the thymus, not the bone marrow. (4) The constant region of the T-cell receptor has no effector function and it does not switch isotype. (5) T-cell receptors do not undergo somatic hypermutation.