Human herpesvirus 8-encoded cytokines
Human herpesvirus (HHV)-8, also called Kaposi's sarcoma-associated herpesvirus, was discovered in 1994 and was rapidly sequenced, revealing several unique and surprising features of its genetic makeup. Among these discoveries was the identification of the first viral homolog of IL-6 and three CC/beta-chemokine ligands (viral CCL-1, -2 and -3), not previously found in gamma-herpesviruses. Viral IL-6 was immediately recognized as a potential contributor to HHV-8 pathogenesis, specifically endothelial-derived Kaposi's sarcoma and the B-cell malignancy multicentric Castleman's disease with which IL-6, a proangiogenic and B-cell growth factor, had previously been implicated. The roles of the viral chemokines were speculated to involve immune evasion; however, like viral IL-6, the viral chemokines have the potential to contribute to pathogenesis through their shared angiogenic activities, known to be important for Kaposi's sarcoma and HHV-8-associated primary effusion lymphoma, and also via direct prosurvival activities. This article will discuss the molecular properties, activities and functions of viral IL-6 and the viral CCLs, proteins that could provide appropriate targets for antiviral and therapeutic strategies.