Modulation of immune responses to bovine herpesvirus-1 in cattle by immunization with a DNA vaccine encoding glycoprotein D as a fusion protein with bovine CD154.

The objective of this study was to determine whether a DNA vaccine encoding bovine CD154 linked to a truncated version of bovine herpesvirus-1 (BHV-1) glycoprotein D (tgD-CD154) induces enhanced tgD-specific immune responses in cattle. In vitro characterization demonstrated that tgD and tgD-CD154 both bind to cultured bovine B cells, whereas only tgD-CD154 induces interleukin-4-dependent proliferation, suggesting that tgD-CD154 specifically binds the CD40 receptor and induces receptor signalling. Calves were immunized with plasmid encoding either tgD or tgD-CD154 by intradermal injection with a needle-free device. After two immunizations, tgD-specific immune responses were observed in both vaccinated groups and after challenge with BHV-1 these responses further increased. Animals immunized with plasmid encoding tgD-CD154 had significantly higher tgD-specific serum titres of immunoglobulins G and A but significantly lower numbers of tgD-specific interferon-gamma-secreting cells than animals immunized with plasmid encoding tgD after BHV-1 challenge. This suggests that the expression of an antigen as a chimeric protein with CD154 can qualitatively alter immune responses in cattle. Since we previously showed that plasmid encoding tgD-CD154 induces significantly enhanced secondary tgD-specific antibody responses in sheep, there appear to be interspecies differences in the immune responses induced by tgD-CD154, which suggests that both proteins in the chimeric molecule may influence protein targeting and the induction of an immune response.