Important note: Information in this article was accurate in 1998. The state of the art may have changed since the publication date.

Reuters NewMedia - Thursday December 17, 1998
Patricia Reaney

Scientists had thought the thymus gland, which produces vital T-cells to fight infections, lost most of its function along with its size as people aged. But Dr Richard Koup and colleagues at the University of Texas Southwestern Medical Center in Dallas, Texas, have shown that contrary to common belief, the thymus gland doesn't stop functioning after puberty, it just slows down.

If scientists could find a way of speeding it up again, it could help revitalize immune systems ravaged by the HIV virus, which causes AIDS, or the powerful chemotherapy drugs used to fight cancer.

"We are hopeful that in HIV infected individuals or patients receiving chemotherapy that ultimately we'll be able to give something to increase the thymus output," Koup said in a telephone interview.

Scientists don't have anything to do that yet, but now they know it may be possible and they have a test to measure how well the thymus is working. Writing in the science journal Nature, the researchers described how they judged how well the gland was functioning by estimating the number of new T-cells it produced.

They found HIV patients treated with highly active anti-retroviral therapy (HAART), a powerful cocktail of drugs, produced new T-cells.

Until now scientists were not sure if the T-cells in the patients were ones left over after the HIV virus attacked the immune system or new cells.

"What we now know is that the thymus is producing new T-cells and that hopefully we will get reconstitution of the immune system. Of course it may take a very long time," said Koup.

HIV patients and people who have had chemotherapy treatment are highly vulnerable to other infections because they have lower than normal levels of T-cells.

The researchers found that as HAART reduced the level of HIV in the body, the number of T-cells rose.

"T-cells can be increased by expanding the few old ones remaining after HIV infection or cancer treatment or through production of new T-cells," Koup said in a statement.

"If T-cells programmed to fight certain infections have been destroyed, they can only be replaced by new T-cells produced by the thymus."

Koup said the HIV virus either infected the cells within the thymus or affected the ability of the gland to produce new T-cells in some unknown way. "Now that we have a way to measure thymus output, we will be able to test therapies that will increase T-cell production," Koup added.

In a commentary in Nature on the research, Hans-Reimer Rodewald of the Basel Institute for Immunology in Switzerland, said the research proved HAART can lead to the production of more new T-cells.

"This means that therapeutic restoration or maintenance of thymic function might be possible," he said.

Australian scientists conducting similar research have shown that temporarily blocking the sex hormones in mice boosted their thymus gland and regenerated their immune systems.

Richard Boyd and Jayne Sutherland, of Monash Medical School in Melbourne, told a recent meeting of the Australasian Society for Immunology in Melbourne that it might also work for HIV patients or people who had had chemotherapy or bone marrow transplants.
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