Induction of immune responses to bovine herpesvirus type 1 gD in passively immune mice after immunization with a DNA-based vaccine

The potential for plasmids encoding a secreted form of bovine herpesvirus type 1 (BHV-1) glycoprotein D (gD) to elicit immune responses in passively immune mice following intramuscular immunization was investigated. In these experiments, 6- to 8-week-old female C3H/HeN or C57BL/6 mice were passively immunized with hyperimmune antisera raised against BHV-1 recombinant, truncated (secreted) gD immediately prior to immunization with plasmids. A single immunization of passively immune mice with plasmid encoding the secreted form of BHV-1 gD resulted in rapid development of both cell-mediated immunity and antibody responses. Furthermore, 50% of mice immunized with a suboptimal dose of recombinant gD formulated into an adjuvant developed significant levels of serum antibodies if mice were pre-treated with hyperimmune antisera. The apparent failure of passive polyclonal antisera to suppress the induction of immune responses to pSLRSV may be related to the immunoglobulin subtypes present in the hyperimmune sera.