The immunomodulatory efficacy of interferon-gamma (IFN-gamma)-associated cytokines coadministered with a plasmid DNA vaccine has been investigated, with variable results. Therefore, to test the immunomodulatory effect of IFN-gamma-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-gamma-associated cytokines and chemokines. These cytokines and chemokines included interleukin-12 (IL-12) and IL-18, as potent inducers of IFN-gamma, and IFN-gamma-inducible protein (IP-10), the production of which is IFN-gamma dependent. A coinjection of either IL-12 or IL-18 strongly suppressed the humoral antibody responses but increased the production of the Th1-type cytokines IFN-gamma 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-gamma 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-gamma. Therefore, IFN-gamma-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.