Natural killer (NK) cells share the same lymphoid lineage as B cells and T cells however unlike their siblings, NK cells do not express antigen-specific receptors.

Instead of responding to antigens found on pathogens, these cells are stimulated by cytokines and other cell signaling molecules and serve to amplify the inflammatory signal initiated by the innate immune response.

NK cells have a large intracellular reservoir of granules containing cytotoxic chemicals. This allows the cells to kill certain types of malignant or infected cells all by themselves after activation.