Mucosal immunization of calves with recombinant bovine adenovirus-3 coexpressing truncated form of bovine herpesvirus-1 gD and bovine IL-6.

Previous studies have suggested an important role of the cytokine adjuvant IL-6 in the induction of mucosal immune responses in animals, including mice. Here, we report the in vivo ability of bovine adenovirus (BAdV)-3 expressing bovine (Bo) IL-6, to influence the systemic and mucosal immune responses against bovine herpesvirus (BHV)-1 gDt in calves. To co-express both antigen and cytokine, we first constructed a recombinant BAdV-3 expressing chimeric gDt.BoIL-6 protein (BAV326). Secondly, we constructed another recombinant BAdV-3 simultaneously expressing gDt and BoIL-6 using IRES containing a bicistronic cassette gDt-IRES.IL-6, (BAV327). Recombinant proteins expressed by BAV326 and BAV327 retained antigenicity (gDt) and biological activity (BoIL-6). Intranasal immunization of calves with recombinant BAV326, BAV327 or BAV308 (gDt alone) resulted in demonstrable levels of gDt-specific IgG responses in sera and IgA response in nasal secretions, in all animals. In addition, all calves developed complement-independent neutralizing antibody responses against BHV-1. However, no significant difference could be observed in the induction of systemic or mucosal immune response in animals immunized with recombinant BAV326 or BAV327 co-expressing BoIL-6. Moreover, there was no difference in the protection against BHV-1 challenge particularly in the amount of virus excretion in the nasal cavity in calves immunized with BAV326, BAV327 or BAV308. These data suggest that the BoIL-6 had no modulating effect on the induction of gDt specific mucosal and systemic immune responses in calves.