Final answer:
TCRs and BCRs are antigen receptors found on T cells and B cells, respectively, and are characterised by a variable antigen-binding region and a constant region. They share a similar structure and genetic diversity mechanism, yet differ in antigen recognition, with TCRs binding only to peptides presented on MHC molecules and BCRs binding directly to free antigens.
Step-by-step explanation:
The T-cell receptor (TCR) and B-cell receptor (BCR) are crucial components of the adaptive immune system and share some common properties:
- Both are membrane-bound receptors specific to their respective lymphocytes – TCRs on T cells and BCRs on B cells.
- Each lymphocyte expresses only one type of antigen receptor, providing specificity to the immune response.
- Both receptors have a variable region that binds antigens and a constant region; however, TCRs have a simpler two-chain structure, while BCRs are part of larger immunoglobulin (Ig) molecules.
- The diversity of antigen-binding specificities in both TCRs and BCRs arises from genetic rearrangement processes.
However, there are also key differences:
- TCRs recognize antigenic peptides only when presented on MHC molecules, whereas BCRs can bind directly to free antigens.
- BCRs can recognize various molecular classes, whereas TCRs are limited to protein epitopes.
- T-dependent antigens require T cell help for B cell activation leading to antibody production, while T-independent antigens do not.