Question

Discuss how T-cell receptors differ from immunoglobulins in the way that they recognize antigen. Use the following terms in your answer: peptides, antigen-presenting cells, MHC molecules, and antigen-binding sites.

Answer 1

T-cell receptors recognize processed peptides presented by MHC molecules on antigen-presenting cells, unlike immunoglobulins which bind directly to intact antigens. TCRs have antigen-binding sites for this specific purpose, while immunoglobulins have a more complex, Y-shaped structure allowing them to recognize a wider array of antigens without MHC presentation.

Step-by-step explanation:

T-cell receptors (TCRs) and immunoglobulins (or antibodies) primarily differ in how they recognize antigens. TCRs interact with processed peptides that are presented by antigen-presenting cells (APCs) with the assistance of MHC molecules. Unlike immunoglobulins which can bind directly to intact antigens, TCRs only recognize antigens that have been digested by APCs, processed into smaller peptides, and embedded within the groove of an MHC molecule on the surface of the APC. The antigen-MHC complex is what the TCRs actually bind to through their antigen-binding sites.

This complex process ensures that T cells are activated appropriately, mainly reacting to foreign antigens presented by APCs, and do not respond to self-antigens, which could lead to autoimmune disorders. Immunoglobulins, which are produced by B cells, have a more variable structure with four peptide chains and a Y-shaped configuration, allowing them to bind directly to intact antigens without the need for processing and presentation by MHC.