How do killer cells kill?

Natural killer (NK) cells are a type of cytotoxic lymphocyte that plays a crucial role in the innate immune system's response to infected or cancerous cells. Unlike T cells, which require prior sensitization to specific antigens, NK cells can recognize and eliminate target cells without prior exposure. The process by which killer cells kill involves several mechanisms, including:

Direct cytotoxicity: NK cells can directly kill target cells through a process known as "direct cytotoxicity." This involves the release of cytotoxic granules containing perforin and granzymes. Perforin creates pores in the target cell membrane, allowing granzymes to enter the cell and induce apoptosis, or programmed cell death.

Antibody-dependent cell-mediated cytotoxicity (ADCC): NK cells can also mediate antibody-dependent cell-mediated cytotoxicity. This process involves the recognition of target cells coated with antibodies produced by B cells. Fc receptors on the surface of NK cells bind to the Fc portion of the antibodies, triggering the release of cytotoxic granules and the subsequent killing of the target cell.

Death receptor signaling: NK cells express death receptors, such as Fas and TRAIL (tumor necrosis factor-related apoptosis-inducing ligand), on their surface. These receptors can bind to their respective ligands expressed on target cells, leading to the activation of caspase cascades and the induction of apoptosis.

Cytokine release: NK cells can release various cytokines, including tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma), upon activation. These cytokines have immunomodulatory effects, promoting inflammation, enhancing the immune response, and directly inducing apoptosis in target cells.

Interaction with other immune cells: NK cells can interact with other immune cells, such as macrophages and dendritic cells, through various receptors and ligands. These interactions can modulate the activity of NK cells and influence the overall immune response.

Overall, killer cells employ multiple mechanisms to kill target cells, including direct cytotoxicity, ADCC, death receptor signaling, cytokine release, and interaction with other immune cells. These mechanisms contribute to the innate immune system's ability to eliminate infected or cancerous cells and maintain immune homeostasis.