What are natural killer cell?

Answer 1

Natural killer cells are non-phagocytic large granular lymphocytes. They kill virus-infected or cancerous cells before adaptive immune response. Natural killer cells recognise abnormal cells by its lack of cell-surface receptors such as major histocompatibility complex class 1 molecules. The natural killer cells will then secret perforin which forms pores in the cell membrane of the target cell. This results in either apoptosis or osmotic cell lysis. Natural killer cells also secrete alpha-defensins, a type of antimicrobial molecule, to directly kill bacteria by disrupting their cell walls.