Construction and immunogenicity of a DNA vaccine containing clumping factor A of Staphylococcus aureus and bovine IL18.

Selection of potent cytokine adjuvants is important for the development of Staphylococcus aureus DNA vaccines. Several potential cytokines have been proven to induce enhanced immune responses in animal models and clinical tests. There is still no reported use of IL18 as an adjuvant to design DNA vaccines against S. aureus. In this study, we cloned the main fibronectin binding protein gene (a fragment from clumping factor A, ClfA(221-550)) of S. aureus and bovine interleukin 18 (bIL18). Then recombinant plasmids were constructed based on the eukaryotic expression vector pVAX1 with or without bIL18. Indirect immunofluorescence assays in transfected HeLa cells indicated that the recombinant DNAs (rDNAs) could be expressed correctly and had antigenicity. BALB/c mice were used as experimental models to examine the immunogenicity of rDNAs in vivo. The ClfA(221-550) rDNA provoked antibody production. The bIL18 rDNA induced production of the Th1 type cytokines IL2 and IFNgamma, and ClfA(221-550) and bIL18 synergistically stimulated T-lymphocyte proliferation. The data demonstrated that bIL18 is a potent adjuvant that could be used to enhance cellular immunity.