Effects of inactivated parapoxvirus ovis on cellular and humoral events of the innate immune response in mice

The immunostimulating properties of inactivated parapoxvirus ovis (iPPVO) have long been demonstrated in vivo and in vitro, yet the biological and molecular mechanisms involved remain largely unknown. We herein report that intraperitoneal inoculation of iPPVO in mice results in stimulation of several events of the innate immune response. Increased interferon I (IFN-I) activity was demonstrated in sera of mice treated with iPPVO at 6 and 12 h post-inoculation (hpi), and enhanced expression of IFN-γ (15-fold increase) and IL-12 (6-fold) mRNA was detected in the spleen of treated mice at 24 and 48 hpi, respectively. A significant increase in neutrophil activity (p < 0.01) was observed at 6 hpi in the blood of iPPVO treated mice. In addition, increased phagocytic activity by peritoneal macrophages of iPPVO-treated mice (p < 0.01) was detected in vivo (from 24 to 72 hpi) and in vitro (12 to 96 hpi). Bactericidal activity of sera mice treated with iPPVO against Escherichia coli was also increased (p < 0.05) at 24 and 72 hpi. Taken together, these results demonstrate that iPPVO administration leads to a transient stimulation of selected innate immune mechanisms, likely contributing to the immunostimulant effects observed against viral and bacterial infections in vivo.