Modulation of immune responses induced by DNA vaccine expressing glycoprotein B of pseudorabies virus via coadministration of IFN-γ-associated cytokines

The immunomodulatory efficacy of interferon-γ (IFN-γ)- associated cytokines coadministered with a plasmid DNA vaccine has been investigated, with variable results. Therefore, to test the immunomodulatory effect of IFN-γ-associated cytokines as vaccine adjuvant, the present study evaluated the immune responses induced by pseudorabies virus (PrV) gB-encoded plasmid DNA vaccine coadministered with IFN-γ-associated cytokines and chemokines. These cytokines and chemokines included interleukin-12 (IL-12) and IL-18, as potent inducers of IFN-γ, and IFN-γ-inducible protein (IP-10), the production of which is IFN-γ dependent. A co-injection of either IL-12 or IL-18 strongly suppressed the humoral antibody responses but increased the production of the Th1-type cytokines IFN-γ and IL-2 from immune T cells. Such antibody suppression was closely related to the increased susceptibility against a virulent viral challenge. On the other hand, IP-10 exhibited enhanced immune responses in both antibody responses and IFN-γ production of immune T cells and facilitated the prolonged survival of infected mice. In contrast, there was no significant change in the immune responses of the mice that received codelivery of IFN-γ. Therefore, IFN-γ-associated cytokines, as Th1-type inducers, can generate unexpected and unwanted effects, and their application as a vaccine adjuvant should be carefully evaluated depending on the target antigens.