Plasmacytoid dendritic cells express TRAIL and induce CD4+ T-cell apoptosis in HIV-1 viremic patients

Artificial Toll-like receptor 7/8 (TLR7/8) ligands can endow plasmacytoid dendritic cells (pDCs) with tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-dependent lytic properties. Keeping in mind that ssRNA serves as natural TLR7/8 ligand, we searched for TRAIL-expressing cells in persons infected with HIV and identified TRAIL+ pDCs in HIV-1 viremic persons, but not in nonviremic and healthy persons. TRAIL expression on pDCs was directly correlated with individual viral loads. Conversely, HIV-1 viremia was found to be associated with the up-regulation of the apoptosis-transmitting receptor TRAIL R1 on activated CD4+ T cells. As a consequence, the latter became susceptible to TRAIL-dependent pDC-mediated killing. In contrast, initiation of antiretroviral therapy led to the up-regulation of apoptosis-inhibiting TRAIL R4 on CD4+ T cells, which subsequently became resistant against pDC-mediated cellular injury. Definition of pDCs as killers of CD4+ T cells implies a new mechanism of disease progression in HIV infection.