The aim of this study was to determine the immunomodulatory effects of IL-12, IL-18 and CD154 (CD40 ligand, CD40L) in DNA-vaccination against the classical swine fever virus. Four recombinant plasmids were constructed including the CSFV coding region for the glycoprotein gp55/E2 alone or together with porcine IL-12, IL-18 or CD154 genes. Five groups of four pigs each were immunized intramuscularly (i.m.) three times with the respective constructs. The control group was inoculated with empty plasmid DNA. Eighteen days after the final immunization, the pigs were challenged with a lethal dose of CSFV strain Eystrup and monitored for a further 16 days. This study showed that co-delivery of IL-18 and CD154 induced an earlier appearance of serum antibodies, reduced B-cell deficiency after infection and protected pigs against a lethal CSFV infection. In contrast, co-delivery of IL-12 led to a reduced titer of neutralizing antibodies and protection against a lethal CSFV challenge in comparison to the other pigs and to pigs that were immunized with a gp55/E2 plasmid alone.