The DNA vaccine vector pcDNA3 induces IFN-alpha production in pigs.

The cytokine inducing capacity of the vaccine vector pcDNA3, a methylated form of the plasmid, and pcDNA3 encoding porcine interleukin (IL)-6 or granulocyte/macrophage colony-stimulating factor (GM-CSF) was studied in pigs, using a model with tissue chambers implanted subcutaneously. The production of interferon (IFN)-alpha, IFN-gamma, IL-6 and GM-CSF was studied at local (tissue chamber fluid (TCF)) and systemic (serum) levels during 3 days post-injection. All forms of the plasmid, except the methylated, induced a transient local production of IFN-alpha but no plasmid-induced production of IFN-gamma, GM-CSF or IL-6 could be detected after injection of the plasmids. The IFN-alpha response increased markedly at repeated injections of pcDNA3. This IFN-alpha inducing capacity of the plasmid is likely to affect immune responses at DNA vaccination of pigs.