hat have not yet encountered their specific antigen - but not in memory T cells - the cloned descendants of cells that have already had such encounters.
The fact that memory T cells lack these specific sequences," the authors note, "suggests that TRECs are diluted during the switch from naive to memory phenotype, presumably as a result of cellular proliferation accompanying this process."
The researchers also found that TREC quantity declines significantly with age. Still, they detected TREC-containing T cells in blood samples from persons as old as 73 years. Elderly persons with intact thymus glands had significantly higher TREC levels than did elderly individuals whose thymus glands had been removed during heart surgery or other medical procedures.
Analysis of blood samples from a group of HIV-infected individuals showed that their TREC levels were significantly lower than TREC levels in blood from age-matched healthy individuals. After receiving HAART, however, all but one of the HIV-infected individuals showed a rapid and sustained increase in TRECs.
Our findings suggest that thymic function is suppressed in HIV-infected individuals and can be improved by reduction of viral load," says Dr. Koup. "Therapies that directly improve thymic function may increase the rate of immune reconstitution after HAART."
The study's project officer, Patricia D"Souza, Ph.D., of NIAID's Division of AIDS, adds, "The next obvious question is to find out what is going on in children being treated for HIV infection. The thymus is much more active in children compared with adults. This technique provides an exciting opportunity to monitor thymic output and immune reconstitution in that population."
NIAID is a component of the National Institutes of Health (NIH). NIAID conducts and supports research to prevent, diagnose and treat illnesses such as HIV disease and other sexually transmitted diseases, tuberculosis, malaria, asthma and allergies. NIH is an agency of the U.S. Department of Health and Human Services.
References: DC Douek, RD McFarland, PH Kelser, EA Gage, JM Massey, BF Haynes, MA Polis, AT Haase, MB Feinberg, JL Sullivan, BD Jamieson, JA Zack, LJ Picker and RA Koup. Changes in thymic function with age and during the treatment of HIV infection. Nature 396, 690-95 (1998).
HR Rodewald. The thymus in the age of retirement (editorial). Nature 396, 630-31 (1998).
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