Blocking Sex Hormones Might Help Restore Immunity

December 16, 1998

TEMPORARY chemical castration could help regenerate the damaged immune systems of people with HIV or who have had chemotherapy or bone marrow transplants. By temporarily blocking sex hormones, suggest researchers in Australia, it may be possible to boost the function of a gland in which vital immune cells develop.

T cells, which attack virus-infected cells and help coordinate the immune system, develop in the thymus gland, deep in the chest. At puberty, the gland shrinks and its internal structure becomes disorganised, so many researchers thought that it ceased to function.

But Richard Boyd and Jayne Sutherland of Monash Medical School in Melbourne have now shown that the thymus remains active in adult mice. The researchers injected a dye into the thymus that marked immature T cells and traced these cells' migration into the bloodstream. They found that the thymus in adult mice was still releasing T cells, albeit at about a tenth of the rate it does in a young animal. The pair reported their findings earlier this month at the Australasian Society for Immunology meeting in Melbourne.

What's more, when Boyd and Sutherland physically castrated some mice, they found that the thymus regained its youthful appearance within four weeks and that the number of T cells it produced increased to near pre-pubertal levels.

"It was astonishing," says Boyd. "The minute we released the sex steroid brake, we got complete regeneration."

In a related study, Richard Koup of the University of Texas Southwestern Medical Center in Dallas and his colleagues measured the levels of a genetic by-product of the release of T cells by the human thymus. Koup's team found that, as in mice, the gland continues to function after puberty at a similarly reduced level. They report their findings in Nature (vol 396, p 690).

Koup also has evidence that the increase in T cell numbers in HIV patients receiving aggressive treatment with combinations of AIDS drugs is caused, at least in part, by the release of T cells by the thymus. This suggests that boosting the gland's function might help to combat AIDS. "It's very encouraging for people with HIV infection," says Bruce Walker of the Massachusetts General Hospital in Boston.

The Australian findings indicate that drugs that suppress the production of sex steroids and partially reverse puberty might boost the immune systems of patients with AIDS or those who have been given immunosuppressive drugs.

With that in mind, Boyd and Anthony Schwarer, head of bone marrow transplants at the Alfred Hospital in Melbourne, are planning to test whether LHRH, or luteinising hormone-releasing hormone, which knocks out the production of sex hormones, also rejuvenates the thymus of adult mice.

Author: Rachel Nowak, Melbourne
New Scientist issue 19/26 Dec 98 - 2 Jan 99


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