NEW YORK, June 13, 2007 — The functioning of thymic nurse cells, which take up other cells known as thymocytes into their bodies, has challenged scientists for decades. Research by Professor of Biology Jerry Guyden and colleagues at The City College of New York (CCNY) sheds new light on the important role they play in the development of T-cells, one of the body’s primary defenses against viruses.

T-cells, which are mature thymocytes and are produced by the thymus, an organ located in the upper portion of the chest, recognize harmful invaders, such as viruses, and then attempt to eliminate disease-infected cells. Thymic nurse cells, which were discovered in 1980 and received their name because of their close relationship with thymocytes, have been reported to be able to take up to 50 thymocytes into their bodies.

Previous studies suggested the nurse cells only took up abnormal thymocytes and killed them. However, Professor Guyden’s research, which was published in the June issue of Experimental Biology and Medicine, shows that the nurse cells ingest both healthy and abnormal thymocytes and then decide which shall die and which shall be allowed to become mature T-cells.

The process is termed MHC restriction, explains Professor Guyden. “This is an important process because if abnormal thymocytes were to mature to become T-cells, they would have the potential to kill healthy cells in the body. During MHC restriction all of the abnormal thymocytes have to be weeded out of the healthy batch.”

The findings of research done in Professor Guyden’s laboratory show the thymic nurse cells retain the abnormal thymocytes inside them but release the healthy ones to mature into T-cells. The researchers obtained their results using a genetically altered mouse system created to study the process.

The genetic alteration in the animals studied allowed all of the developing T-cells in the female mice to live while all of the thymocytes in the male mice were killed. If, as previous researchers had found, thymic nurse cells only took up the defective thymocytes that were slated to die, one would have expected to find a high number of nurse cells in male mice but none in the females.

However, the results showed a significantly larger number of thymic nurse cells in female mice than in male mice. These data show that the nurse cells are capable of taking up thymocytes that had been selected to live to become mature T-cells as well as those selected to die.

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