Immunomodulatory functions encoded by the E3 transcription unit of adenoviruses

Persistent viruses have evolved multiple strategies to escape the host immu ne system. One important prerequisite for efficient viral reproduction in t he face of an ongoing immune response is prevention of premature lysis of i nfected cells. A number of viruses achieve this goal by interfering with an tigen presentation and recognition of infected cells by cytotoxic T cells ( CTL). Another viral strategy aims to block apoptosis triggered by host defe nse mechanisms. Both types of strategies seem to be realized by human adeno viruses (Ads). The early transcription unit E3 of Ads encodes proteins that inhibit antigen presentation by MHC class I molecules as well as apoptosis induced by tumor necrosis factor alpha (TNF-alpha) and Fas ligand (FasL). Here, we will describe the organization of the E3 regions of different Ad s ubgroups and compare the structure and functions of the known immunomodulat ory E3 proteins.