The serological response of sheep to DNA immunisation against Toxoplasma gondii

Abstract

The administration of DNA vaccine has been suggested as a promising method to increase specific humoral and cellular immune response against Toxoplasma gondii (T. gondii) infection. In the current study, the serological (immunoglubins IgG1 and IgG2) responses of sheep to DNA vaccination against T. gondii were evaluated. The cloned plasmid DNA containing protective T. gondii antigens, ROP1, GRA7, MIC3, GRA1, GRA6 and MAG1 were transformed and grown in Escherichia coli cells and purified. Three groups of coopworth twelve month old ewes (n=40) were immunised by intramuscular injection with the combination of purified plasmids pVAXROP1/CD154+pVAXIgGRA7+pVAXMIC3 and/or pVAXIgGRA1+pVAXIgGRA6+pVAXMAG1 separately, as well as plasmid encoding CpG oligodeoxynucleotide and liposomes as adjuvants. Another group of ewes (n=40) were injected with phosphate buffered saline solution as controls. The injections were applied twice intramuscularly with a four weeks interval between injections. Production of IgG1 and IgG2 antibodies were studied by the use of enzyme linked immunosorbent assays, with the optical density ratio representing antibody titre response. The first and second immunisations with the combination of plasmids pVAXROP1/CD154+pVAXIgGRA7+pVAXMIC3 produced high (P<0.001) level of specific anti-ROP1 IgG1 antibody in the serum. This indicates that this technique could stimulate strong humoral immune response, and therefore has promise for development of a commercial Toxoplasma vaccine.