Smith A, Santoro F, Di Lullo G, Dagna L, Verani A, Lusso P. Unit of Human Virology, DIBIT-San Raffaele Scientific Institute, Via Olgettina n 58, Milan 20132, Italy. email@example.com Blood. 2003 Oct 15;102(8):2877-84.
Human herpesvirus 6 (HHV-6) is a potentially immunosuppressive agent that has been suggested to act as a cofactor in the progression of HIV disease. Exposure of human macrophages to HHV-6A or HHV-6B profoundly impaired their ability to produce interleukin 12 (IL-12) upon stimulation with interferon-gamma (IFN-gamma) and lipopolysaccharide (LPS).
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By contrast, the production of tumor necrosis factor-alpha (TNF-alpha); regulated on activation, normal T-cell expressed and secreted (RANTES); and macrophage inflammatory protein 1beta (MIP-1beta) was not negatively affected. To exclude the involvement of IL-12-suppressive cytokines, such as IL-10 and TNF-alpha, the viral stocks were fractionated by ultra- centrifugation. The bulk of the suppressive activity was recovered within the virion-rich pelleted fraction that was virtually devoid of such cytokines. IL-12 suppression was independent of viral replication, and the effect was not abrogated upon ultraviolet-light inactivation of the viral inoculum.
The mechanism of HHV-6-mediated IL-12 suppression was investigated by RNase protection assays, which demonstrated unaltered levels of IL-12 p35 mRNA and only a modest reduction in p40 mRNA, which was insufficient to account for the near-complete loss of both extracellular and intracellular IL-12 protein.
Moreover, both the IFN-gamma and the LPS signaling pathways were intact in HHV-6-treated cells. These data suggest that HHV-6 can dramatically affect the generation of effective cellular immune responses, providing a novel potential mechanism of HHV-6-mediated immunosuppression.