Question

1. What are the functionally distinct domains (regions) of antibody and TCR molecules?

2. What are the differences in the types of antigens recognized by antibodies and TCRs?
3. What mechanisms contribute to the diversity of antibody and TCR molecules?

Answer 1

1. Human antibodies are large Y-shaped proteins that are used by the immune system to defend against threats such as viruses or bacteria. The two arms of the Y are called fragment antigen-binding (FAB) regions. Each FAB region consists of a heavy and light chain that are both subdivided into a constant and a variable region.

T-cell receptors (TCRs) are membrane bound surface receptors of T-cells .TCRs consist of an α-chain and a β-chain that are both subdivided into a variable and a constant region.Variable domains contain hypervariable regions (sequences that differ among different antibodies or TCRs) that form the binding sites for antigens.

2. Antibodies recognise bacteria virus and all types of foreign bodies enter the body, in contrast to antibodies TCRs only recognize small and continuous peptide antigens that are presented via the MHC of antigen presenting cells to them

3. Antibody modes of operation include neutralization in which a part of an antigen surface is blocked, agglutination in which assemblies of antibodies trigger phagocytosis, precipitation in which assemblies of antibodies force antigens to precipitate out of solution, and complement system activation. Antibodies can act in their soluble form without being bound to a cell membrane and can recognize discontinuous antigens.

TCRs do not act directly against antigens but trigger a signaling cascade inside the T-cell for further actions.