Cytotoxic T lymphocyte-mediated cell killing

Cytotoxic T lymphocyte-mediated cell killing is the process by which cytotoxic T lymphocytes (CTLs, typically CD8+ T cells) recognize and destroy target cells—such as those infected by viruses, transformed (cancerous) cells, or allogeneic (transplanted) cells. Target cell recognition is achieved via the T cell receptor (TCR) binding to foreign peptides presented on major histocompatibility complex class I (MHC I) molecules on the target cell. The killing mechanism involves the exocytosis of cytotoxic granules containing perforin (which forms pores in the target cell membrane), and granzymes (serine proteases that enter the cytosol and trigger apoptosis). Additionally, Fas ligand (FasL) expressed by activated CTLs can bind to Fas on target cells to induce apoptosis via the extrinsic pathway. This precision killing plays a key role in the immune system's defense against intracellular pathogens and malignant cells, with critical implications in infection control, tumor immunology, and autoimmunity.

Induction of apoptosis in target cells by cytotoxic T lymphocytes via delivery of granzymes and perforin, or engagement of Fas ligand (FasL) with Fas on the target cell