Human cytomegalovirus (HCMV) can suppress and evade the immune system. We have identified as a mechanism the ability of HCMV to infect dendritic cells (DC), which initiate the antiviral immune response. HCMV-infected DC show enhanced expression of costimulatory molecules. In contrast, MHC molecules are partially downregulated, leading to a reduced antigen-presenting capacity. Moreover, the apoptosis-inducing ligands CD95L (FasL) and tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) are upregulated, thereby enabling HCMV-infected DC to delete activated T lymphocytes. This additional layer of viral defense is complemented by nondeletional mechanisms, which suppress surviving T cells. Thus, infection of DC allows the virus to blunt the antiviral T cell response by a multilayered defense strategy and could play a pivotal role in HCMV-triggered immunosuppression.
