Role of interleukin-18 in peripheral blood mononuclear cells infected with human herpes virus type 6

Objective. Il-18 production represents a critical step in the polarization of the Th1 immune response. HHV-6 possesses a peculiar tropism for immunocompetent cells. To understand the relationships among immunocompetent cells, HHV-6 and cytokines, the role of IL-18 during infection of PBMC with HHV-6 was evaluated. Methods. PBMC were obtained from healthy donors, after centrifugation of heparinized venous blood over Ficoll-Hypaque gradient.Supernatants from PBMC, were analysed for the presence of cytokines by immunoenzimatic method.In order to study the effects of exogenous rhIL-18 on HHV-6 replication were analysed the number of cells expressing viral antigens by IFA and the amount of extracellular virus by f.f.u./ml. Results.No basal production of IL-18 was found in supernatants of unstimulated PBMC. Appreciable amounts of the cytokines were produced by LPS-stimulated PBMC. HHV-6 infection of LPS-treated PBMC downregulated IL-18 production. It was found that the addition of rhIL-18 to HHV-6 infected PBMC downregulated the percentage of HHV-6 antigen positive cells and the release of extracellular virus. Conclusion. Impairment of IL-18 release, which is involved in the induction of antiviral cytokines such as IFN, could represent a strategy of the virus to evade the immune response of the host, thus establishing its own persistent infection.