Immunization with plasmid DNA expressing the caprine arthritis-encephalitis virus envelope gene: quantitative and qualitative aspects of antibody response to viral surface glycoprotein.

Saanen goats were vaccinated intradermally with plasmid DNA expressing caprine arthritis-encephalitis virus (CAEV) rev-env (pENV) or tat-rev-env (pTAT-ENV) or vaccinia virus expressing CAEV env (rWR-63). Sera from all vaccinated goats immunoprecipitated CAEV surface (SU) and transmembrane (TM) glycoproteins with a dominant response to SU. Antibody response to CAEV SU induced by plasmid DNA was relatively biased toward IgG2, whereas vaccinia rWR-63 induced predominantly IgG1 antibodies to SU. Differential IgG isotype bias established by immunization with plasmid or vaccinia vectors was maintained following subcutaneous boost with purified CAEV SU in Freund's incomplete adjuvant (FIA). Goats injected with pUC18 control plasmid followed by immunization with SU-FIA also had IgG2 biased responses, whereas SU-FIA immunization of a goat primed with vaccinia rWR-SC11 without the CAEV env gene induced a predominant IgG1 response. We conclude that pUC based plasmids expressing the CAEV env gene promote stable type 1 biased immune responses to plasmid encoded SU. IgG2 biased response may be due to innate type 1 priming capacity of immunostimulatory CpG motifs in the pUC ampicillin resistance gene.