Final answer:
Death receptors transmit signals for apoptosis upon binding death ligands such as the Fas ligand. The Fas ligand, expressed on NK and cytotoxic T cells, plays a critical role in immune response and development by inducing apoptosis in targeted cells.
Step-by-step explanation:
Death receptors are cell surface proteins that transmit apoptosis signals on binding death ligands, like Tnf-α and the Fas ligand. The Fas ligand is a molecule expressed on cytotoxic T cells and NK cells that binds to the Fas molecule on a target cell and induces it to undergo apoptosis. This process is crucial for the immune response, as it allows for the regulated destruction of infected or damaged cells without causing harm to neighboring healthy cells.
NK cells are effective in the immune response due to their ability to express the Fas ligand, responding to chemical signals, and binding to the Fas molecule on the surface of infected cells. This interaction sends apoptotic signals, leading to the elimination of the infected cell and any pathogens within it. Similar mechanisms are at play in the development of T-cells, where apoptosis is initiated if a T-cell receptor binds to self proteins, preventing autoimmune diseases.
Moreover, apoptosis is essential in normal development, such as the elimination of cells between developing digits, enabling the proper separation of fingers and toes in vertebrates. A cell signalling mechanism triggers apoptosis for this purpose.