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Correspondence to: David D. Ho, Aaron Diamond AIDS Research Center, The Rockefeller University, 455 First Ave., New York, NY 10016. Tel:212-448-5000 Fax:212-725-1126 E-mail:dho{at}adarc.org.
The role of the thymus in HIV-1 pathogenesis remains unclear. We developed an assay to quantify the number of recent thymic emigrants in blood based on the detection of a major excisional DNA byproduct (termed
1 circle) of T cell receptor rearrangement. By studying 532 normal individuals, we found that
1 circle numbers in blood remain high for the first 1015 yr of life, a sharp drop is seen in the late teen years, and a gradual decline occurs thereafter. Compared with age-matched uninfected control individuals,
1 circle numbers in HIV-1infected adults were significantly reduced; however, there were many individuals with normal
1 circle numbers. In 74 individuals receiving highly active antiretroviral therapy, we found no appreciable effect on
1 circle numbers in those whose baseline values were already within the normal range, but significant increases were observed in those with a preexisting impairment. The increases in
1 circle numbers were, however, numerically insufficient to account for the rise in levels of naive T lymphocytes. Overall, it is difficult to invoke thymic regenerative failure as a generalized mechanism for CD4 lymphocyte depletion in HIV-1 infection, as
1 circle numbers are normal in a substantial subset of HIV-1infected individuals.
Key Words: HIV, thymus gland, aging, pathogenesis, drug therapy
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