RECOMBINANT PORCINE IFN-GAMMA POTENTIATES THE SECONDARY IGG AND IGA RESPONSES TO AN INACTIVATED SUID HERPESVIRUS-1 VACCINE AND REDUCES POSTCHALLENGE WEIGHT-LOSS AND FEVER IN PIGS

The effect of recombinant porcine interferon-gamma (IFN-gamma) on the immunogenicity ill vivo of inactivated suid herpesvirus-1 (SHV-1, Phyl axia strain) was studied applying two successive i.m, immunizations. T he animals were injected with inactivated virus alone or inactivated v irus supplemented with 10(4) or 10(6) U IFN-gamma. After the first imm unization, none of the animals responded with measurable virus-neutral izing antibody (VNAb), virus-specific IgG or IgA, Following a second i mmunization 4 weeks later, a significantly increased VNAb response was noted in animals that had received vaccine doses containing 10(4) U I FN-gamma (p < 0.05). These animals also had significantly augmented se rum levels of IgG (p < 0.01) and IgA (p < 0.05). Inclusion of 10(6) U IFN-gamma in the vaccine preparation did not affect the antibody respo nse. In one experiment, the pigs were challenged oronasally with 10(5) TCID50 of the 75V19 strain of SHV-1, 7 weeks after administration of the second vaccine dose. Those that had received 10(4) U IFN-gamma in the vaccination developed less fever during the postchallenge period ( p < 0.004). In all challenged pigs, growth performance was compromised during the first week after challenge. However, the only animals reta ining an average net increase in body mass were those covaccinated wit h 104 U IFN-gamma (p < 0.05). Nasal excretion of virus was not signifi cantly different between groups that had been vaccinated with or witho ut IFN-gamma. Multiple linear regression analysis of variables from in dividual vaccinated animals revealed the VNAb response to be correlate d with serum IgG levels (p < 0.025) and with postchallenge growth perf ormance (p < 0.0001) but not with serum IgA levels (p > 0.5), On the o ther hand, serum IgA appeared to be inversely correlated with early na sal virus excretion after challenge (p < 0.006), Taken together, our d ata suggest that addition of IFN-gamma to inactivated SHV-1 vaccine ma y be a useful tool for enhancement of both mucosal and systemic immune responses in pigs.