Immunomodulatory effects of inactivated parapoxvirus ovis (ORF virus) on human peripheral immune cells: induction of cytokine secretion in monocytes and Th1-like cells.

Inactivated parapoxvirus ovis (Orf virus; PPVO) recently displayed strong immunostimulating and modulating capacities in several animal models for acute and chronic virus infections through the induction of gamma interferon (IFN-gamma) as a key mediator of antiviral activity. The data presented in this work demonstrate that inactivated PPVO has strong effects on cytokine secretion by human immune cells, including the upregulation of inflammatory and Th1-related cytokines (IFN-gamma, tumor necrosis factor alpha [TNF-alpha], interleukin 6 [IL-6], IL-8, IL-12, and IL-18) as well as anti-inflammatory and Th2-related cytokines (IL-4, IL-10, and IL-1 receptor antagonist [IL-1ra]). Studies on the mechanism of action revealed virus particles to be the effective components of the preparation. The virus particles activate monocytes or other antigen-presenting cells (APC), e.g., plasmacytoid dendritic cells, through signaling over CD14 and a Toll-like receptor and the intracellular presence of certain PPVO-specific components. The activation of monocytes or APC is followed by the release of early proinflammatory cytokines (TNF-alpha, IL-6, and IL-8) as well as the Th1-related cytokines IL-12 and IL-18. Both IL-18 and IL-12 are involved in PPVO-mediated IFN-gamma release by T cells and/or NK cells. The proinflammatory response is accompanied by the induction of anti-inflammatory and Th2-related cytokines (IL-4, IL-10, and IL-1ra), which exert a limiting efffect on the inflammatory response induced by PPVO. We conclude that the induction of a natural immune response with physiologically significant amounts of different cytokines and with antiviral potential might provide advantages over existing antiviral immunotherapies.