Antibodies are in the frontline of an animal's defence against foreign invaders. They bind to viruses and bacteria, for example, and help to destroy them, so it is not surprising that antibody-based treatments are being used in a variety of ways. But while antibodies target foreign molecules, they cannot kill cells, such as cancerous ones, without the help of molecules that are attached to them by chemical manipulation. Specific toxins are the most common molecules used as the payload attached to antibodies, which act as the messengers to deliver them to the target. In some cases, such as Rituxan, the treatment used against blood cancer, the toxins are thought to trigger the cancer cells to commit suicide, a process called apoptosis. The antibodies act on the surface of cells - because normally they cannot penetrate them - in a process initiated by receptors on the surface of cells that are bound together or cross-linked.
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