Important note: Information in this article was accurate in 1999. The state of the art may have changed since the publication date.

Reuters NewMedia - Thursday May 27, 1999

They said they had found evidence that the organ, located in the chest, keeps producing the cells -- named T-cells -- at least until the age of 56. This finding could be good news for people infected with the HIV virus, which attacks T-cells, the team at the University of California Los Angeles said. It might be possible to recruit the thymus to fight the deadly infection, they wrote in their report, published in the journal Immunity.

The finding also offers hope to cancer patients whose bone marrow -- the main source of immune cells -- is damaged or destroyed by harsh chemotherapy and radiation therapy. Currently such patients must undergo a bone marrow or stem cell transplant.

"Our study focused on exploring three unknowns about the adult thymus," Beth Jamieson, who led the study, said in a statement.

"Does the thymus function the same at age 50 as it does at age 5? Does it follow the same process to produce T-cells? And do these T-cells possess the same diversity of surface markers and receptors? The answer to all three questions was a resounding yes."

Like other immune cells, the T-cell starts out in the bone marrow as a stem cell, a kind of master cell that can become one of any number of cells. It migrates to the thymus where it is taught how to be a T-cell, whose job in part is to meet invaders the first time they enter the body and recognize them the next time, thus helping orchestrate a quicker response.

"The thymus operates like a boot camp that trains T-cells to attack specific enemies," said Jerome Zack of UCLA's AIDS Institute, who worked on the study. "Thymocytes (T-cells) must make the pilgrimage through the thymus and fully evolve before they can help the body fight infection."

But it was thought the thymus stopped working after puberty. The organ withers and becomes fatty with age.

Jamieson and Zack decided to check and see if the thymus really stopped working. They took T-cells from adult thymus tissue and examined them.

"We discovered CD4 (so-called helper T-cells) and CD8 ("killer") T-cells went through all the main stages of development," Jamieson said.

They also looked the same as fetal T-cells, she said.

"Our findings suggest that thymocytes develop and mature in the adult thymus as they do in the fetal thymus," she added. "Contrary to previous scientific belief, the thymus continues to function late in life."

So the body has a source of fresh recruits to fight infection, Zack said. "This means that when our body contracts a disease, the thymus issues new T-cells to combat infection," he said. "Our immune system is not relying solely on old T-cells that the thymus produced before puberty."
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Always watch for outdated information. This article first appeared in 1999. This material is designed to support, not replace, the relationship that exists between you and your doctor.

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