Viral immunomodulatory proteins: usurping host genes as a survival strategy

Large DNA-containing viruses encode a plethora of gene products that are homologous to cellular proteins and key for their success in nature. During the millions of years of co-evolution with their respective hosts, viruses have extensively captured cellular genes, frequently duplicated them and insidiously shaped them to yield optimized specific molecules capable of either mimicking or interfering with the original host function and/or of executing novel tasks. A vast number of these gene products have become an integral part of the elaborated counteracting immune evasion strategies developed by viruses to withstand with the selective evolutionary pressure imposed by the host immune system. Cytomegaloviruses (CMVs) constitute an outstanding example of the many and varied encoded proteins directed to modulate both innate and adaptive immune responses, which determine their ability to establish life-long latency with sporadic shedding in their hosts. This chapter focuses on the current understanding of those genes encoded by human CMV (HCMV) with a known homology to cell proteins of the immune system. A systematic study of these genes, in addition to unraveling specific virus-host interactions, may supply valuable tools to dissect the molecular basis of immune responses.