CAROL AND MIKE WERNER / SCIENCE PHOTO LIBRARY CAROL AND MIKE WERNER / SCIENCE PHOTO LIBRARY
Natural killer cells (upper left). Natural killer cells (also known as NK cells, K cells, and killer cells) are a type of lymphocyte (a white blood cell) and a component of autoimmune system. A group of proteins known as Human Leukocyte Antigens (HLA) -- shown in green on the cell lower right -- shut down killer cell activity. HLA is found on the surface of healthy cells but not on tumours or cells infected by viruses (upper right), leaving them open to attack by killer cells. Killer cell immunoglobulin-like receptors (KIR) allow Killer cells to recognize the HLA molecules.
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