Our immune system is constantly on the lookout for cells that are not acting normally. Changes can occur due to infection with a virusThe smallest type of organism known. A single virus particle (called a virion) is much smaller than a cell. Viruses reproduce by invading cells and forcing the cells to make progeny virions. Viruses generally have specific host cells which they infect. Some virus types are associated with specific cancers and can convert normal cells into cancer cells. Examples of viruses associated with cancer are: papillomavirus-cervical cancer, hepatitis virus-liver cancer, Epstein-Barr virus-Burkitt's lymphoma. Virus-induced transformation of cells was one of the very first model systems for the study of cancer. Viruses have also been a key tool in the identification of many oncogenes. Because of their great ability to enter target cells viruses such as adenoviruses are being examined for their ability to deliver genes to cancer cells. or the conversion of a normal cell to a cancer cell. Abnormal cells are killed by having holes 'punched' in their membranes. The proteins that perform this function, perforins, have now been examined at the molecular level, providing a better understanding of the process. The results should make it easier for researchers to find ways of helping the immune system identify and kill cancer cells that have found ways to avoid detection.
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