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Date: Thursday, June 6, 1996 FOR IMMEDIATE RELEASE Contact: Michael Miller (301)496-1752
Research by scientists at the National Institutes of Health (NIH) and the Naval Medical Research Institute (NMRI) sheds light on how an enzyme, telomerase, which regulates the rate of growth at the tips of DNA, might influence immune function.
The scientists have discovered that telomerase is present at high levels during both the development and activation stages of immune cells and that this may affect the way the immune system is turned on and regulated. Their research is published in the June issue of The Journal of Experimental Medicine. Only recently have scientists found that telomerase, previously thought to be present only in "immortal" cells like sperm, egg, and tumor cells, is also present in normal human immune cells.
Telomerase regulates DNA length by replenishing the ends of DNA strands, called telomeres. These end segments are thought to be responsible, in part, for maintaining the structural integrity of DNA. In most types of cells, telomeres shorten as the cell ages, but in tumor cells, and also in normal immune cells, telomerase might help slow this shortening, according to National Institute on Aging (NIA) scientist, Dr. Nan-Ping Weng and NIA Director,
Dr. Richard J. Hodes working at the National Cancer Institute and their colleagues, Drs. Bruce L. Levine and Carl H. June from the NMRI. When investigating how telomerase affects immune function, Weng's group looked at T-lymphocytes, one of the types of immune cells found in the body, particularly in the blood. Substantial lymphocyte cell division is essential for effective immune response to invading viruses or bacteria. "Because of this unique feature, lymphocytes provide an ideal system in which to study the regulation of telomeres and the relationship between telomere length, telomerase activity, and the potential for cells to replicate," says Weng.
By looking at T-lymphocytes from three different sources, the thymus, the tonsil, and peripheral blood, the NIA researchers were able to show that telomerase is active at different stages of lymphocyte development. Starting with the early development of T- lymphocytes in the thymus gland, Weng's group detected telomerase activity. After the lymphocytes reached the peripheral blood and cell growth was in a resting state, little telomerase activity was detected. If the cell was induced to proliferate, telomerase activity was seen again. Thus, the investigators gained insight into when and where telomerase is active. Weng and his associates are already trying to answer the next questions of how and why telomerase is turned on, and what role telomerase may play in lymphocyte development and activation.
Other researchers, in 1994, suggested that telomerase may be the key to regulating tumor growth. The current research should bring new caution to this avenue of exploration. What Weng and associates have found might influence the strategies being considered by tumor biologists to use telomerase-blocking drugs to fight cancer, as these drugs may hinder crucial cancer-fighting immune cells such as lymphocytes.
Using normal cells like lymphocytes to study telomerase activity may help in figuring out the workings of this enzyme. Key questions remain about the real function of telomerase in cell growth, be it in cancer cells or immune cells, and what chain of events initiates its activity. Weng and his collaborators say that multiple signals may influence telomerase function. Their studies of lymphocytes could provide a model system for studying regulation of telomerase activity.
The National Institute on Aging and the National Cancer Institute are both part of the National Institutes of Health, and of the Department of Health and Human Services (DHHS). The NIA leads the Federal efforts on research on aging and the special needs of older people.