HIGH PREVALENCE OF THYMIC TISSUE IN ADULTS WITH HUMAN IMMUNODEFICIENCY VIRUS-1 INFECTION

The thymus in adults infected with the HIV-1 is generally thought to b e inactive, both because of age-related involution and viral destructi on. We have revisited the question of thymic function in adults, using chest-computed tomography (CT) to measure thymic tissue in HIV-l-sero positive (n = 99) or HIV-l-seronegative (n = 32) subjects, and correla ting these results with the level of circulating CD4(+) and CD8(+) T c ells that are phenotypically described as naive thymic emigrants. Abun dant thymic tissue was detectable in many (47/99) HIV-l-seropositive a dults, aged 20-59. Independent of age, radiographic demonstration of t hymic tissue was significantly associated with both a higher CD4(+) T cell count (P = 0.02) and a higher percentage and absolute number of c irculating naive (CD45RA+CD62L+) CD4(+) T cells (P < 0.04), The preval ence of an abundant thymus was especially high in younger HIV-l-seropo sitive adults (less than or equal to 39 yr) with CD4 counts in the ran ge 300-500 cells/mu l and in older subjects (> 40 yr) regardless of CD 4 count (P = 0.03). These studies suggest that the thymus is functiona l in some but not all adults with HIV-1 disease.