Humoral immune responses to DNA vaccines expressing secreted, membrane bound and non-secreted forms of the Tania ovis 45W antigen.

The antibody response to DNA vaccines expressing secreted, membrane bound and non-secreted forms of the same antigen was investigated. The antigen gene selected for these studies was the full length 45W antigen gene from Taenia ovis. This gene encodes a host protective membrane bound antigen with a native secretion signal at the amino terminus and a hydrophobic anchor domain at the carboxyl terminus. Full length and rationally truncated forms of the 45W antigen gene were generated and used to construct DNA vaccines encoding membrane bound, secreted and non-secreted forms of the 45W antigen. The cellular localisation of these antigen forms was confirmed by Western blot studies. BALB/c mice were immunised intramuscularly with plasmid DNA and serum antibody responses measured by enzyme linked immunosorbant assay (ELISA). The cellular localisation of DNA vaccine antigen had a significant effect on the magnitude but not the subclass of antibody responses. Immunisation with DNA expressing secreted 45W generated three-fold higher antibody titres than immunisation with DNA expressing membrane bound 45W, and 18-fold higher antibody titres than DNA expressing non-secreted 45W. All mice generated a predominantly IgG1 antibody response indicative of a TH-2 type immune response. These results indicate that the optimal induction of humoral immune responses to intramuscular genetic immunisation with the 45W antigen, requires the active secretion of antigen. This observation may be of value during the design of DNA vaccines in the future.