The bovine herpesvirus type 1 major tegument protein VP8 expressed in recombinant vaccinia virus does not induce significant immunity in mice

We previously reported the characterization of the gene encoding the bovine herpesvirus type 1 (BHV-1) major tegument protein VP8. With the aim of defining the immunological properties of this protein, we constructed a recombinant vaccinia virus (VV-VP8) in which expression of the VP8 gene was regulated by the P7.5 early/late promoter. Since the sequence of the VP8 gene contained a TTTTTTNT motif known to serve as a transcription termination signal of vaccinia virus genes of the early class, a second recombinant (VV-VP8-Mut) in which this signal was modified by site-directed mutagenesis was created. Characterization of the recombinant viruses revealed that truncated VP8 mRNA and protein (69 kDa) were synthesized in VV-VP8 infected cells, whereas cells infected with VV-VP8-Mut produced a protein which was undistinguishable from that of the BHV-1 encoded protein (92-94 kDa). Immunization of BALB/c mice (H-2(d)) with VV-VP8-Mut induced a low VP8-specific antibody response whereas no specific response was induced in VV-VP8 inoculated mice. The low humoral response elicited was similar in C57BL/6 (H-2(b)) and C3H (H-2(k)) mice. Furthermore, immunization of mice with VV-VP8-Mut did not induce a BHV-1-specific lymphoproliferation in the three mice strains examined. Our results contrast with a recent study showing that immunization of calves with purified VP8 stimulated both T cell proliferation and antibody production.