Enhanced th1 immune responses induced with an ova-il-12 fusion protein

The form of immunity that occurs during a particular immune response is dependent on the development of T cells producing specific, restricted cytokine profiles. In order to direct the form of the immune response in an antigen-specific manner, we constructed a cytokine fusion protein (OVA-IL12) that contained the T cell-dependent antigen ovalbumin (OVA), fused to murine IL-12. The OVA-IL-12 fusion protein was produced in a baculoyirus expression system and was purified by anti-OVA immunqaffinity chromatography. The purified OVA-IL-12 protein was characterized by SDS-PAGE and by Western blot analysis using anti-OVA and anti-p40 antibodies, and displayed potent IL-12 bioactivity in an IL-12 proliferation assay. BALB/c mice immunized with the OVA-IL-12 fusion protein produced increased quantities of anti-OVA lgG2a, but decreased anti-OVA-lgG1 antibody compared with mice immunized with recombinant OVA alone. Spleen and lymph node cells from the immunized mice produced large amounts of IFN-y when restimulated in vitro with OVA, while those from mice immunized with the OVA alone or from non immunized mice produced little or no IFN-y. In contrast, immunization with OVA and free rlL-12 enhanced T cell production of IFN-y, but the IFN-y production was not antigen-specific. Moreover, the OVA-IL-12 protein was effective in enhancing IFN-y production in OVA-primed mice. BALB/c mice previously injected with OVA in alum and subsequently immunized with the OVA-IL-12 protein developed a significant increase in antigen-specific IFN-y production and a significant decrease in antigen-specific IL-4 production. These studies indicate that the OVA-IL-12 fusion protein can induce OVA-specific Th1 responses, and that the fusion protein confines the effect of IL-12 to OVA-specific T cells.