Correlation between the nature of immunity induced by different immunogens and the establishment of latent infection by wild-type pseudorabies virus.

To assess the correlation between the nature of immunity induced by different types of immunogens and the establishment of latent infection by wild-type pseudorabies virus (PrV), we used a murine model immunized with different immunogens, the PrV modified live vaccine (MLV), inactivated vaccine (IAV), and commercial oil-adjuvant subunit vaccine (OSV), via either intranasal (i.n.) or intramuscular (i.m.) route. Both MLV and IAV induced a different nature of immunity biased to Th1- and Th2-type, respectively, as judged by the ratio of PrV-specific IgG isotypes (IgG2a/IgG1) and the profile of cytokine IL-2, IL-4, and IFN-gamma production. In contrast, the OSV induced a lower isotype IgG2a to IgG1 ratio and higher level of IL-2 production. The MLV (inducing Th1-type) provided more effective protection against a virulent wild-type PrV challenge than IAV and OSV (inducing Th2- and mixed type, respectively). In addition, the MLV impeded the establishment of a latent infection with wild-type PrV, and the decrease in the PrV latency load by immunization with the MLV appeared to be mediated by the immune T-cells. These results demonstrate the substantial role of the immune responses driven by preceding vaccination in modulating the establishment of PrV latency caused by the post-infection of a field virus.