CELLS ALIVE! / SCIENCE PHOTO LIBRARY CELLS ALIVE! / SCIENCE PHOTO LIBRARY
Cytotoxic T lymphocyte killing influenza-infected cell. Lymphocytes can learn to recognize cells that are infected with viruses or that are cancerous. They attack and kill these cells. The smaller cell is the T cell, the larger one the infected cell. T-cells are the ones that drop in number in people with AIDS.
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