The Fas/FasL system and T cell apoptosis in HIV-1-infected lymphoid tissue during highly active antiretroviral therapy.

Apoptosis has been proposed as a mechanism responsible for T cell depletion in HIV-1 infection. In the present study we have phenotyped apoptotic T cells in tonsillar lymphoid tissue from 11 HIV-1-infected patients by flow cytometry light-scatter characteristics during 48 weeks of highly active antiretroviral therapy (HAART). We found that the decline in tonsillar viral load was associated with a decrease in the proportion of apoptotic CD4+ and CD8+ T cells. CD4 cell apoptosis was predominantly seen within the memory CD28+ Fas+ FasL+ population. The increased level of apoptotic CD8+ T cells was found among activated Fas+ memory cells irrespective of CD28 and FasL expression. These T cell subsets were expanded in untreated infection, but normalized with therapy. We conclude that HIV-1 triggers FasL-mediated apoptosis of uninfected CD4+ T cells, whereas CD8+ T cell apoptosis is driven by chronic immune activation. Virus suppression reverses both of these mechanisms, contributing to immune reconstitution during HAART. Copyright 2001 Academic Press.