Natural Killer Cells Definition

Natural Killer Cells – a granular lymphocyte (white blood cell with granules in its cytoplasm) that has cytotoxic (cell-killing) functions within the immune response. NK cells belong to the cellmediated immunity pathway of the immune response and do not require antigen presentation to target a cell for destruction. NK cells are particularly involved in killing tumor cells.

They release molecules that puncture or perforate (make molecular holes in) the cell membrane of the cell under attack. This assault may directly kill the cell or cause accelerated apoptosis (planned cell death) that the target cell itself initiates in response to the damage it experiences.

For further discussion of natural killer cells within the context of the structures and functions of the immune system, please see the overview section “The Immune System and Allergies.”


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