Enhancement Of The Immune Responses To Pseudorabies Vaccines Using Ginseng Stem-leaf Saponins And Selenium

Pseudorabies(Pr)also known as Aujeszky’s disease(AD)is a highly contagious viral infection that can cause reproductive failures in pregnant sows,respiratory problems in adult animals,neurological signs and diarrhea in piglets leading to high mortality and thus brings substantial economic losses to swine industry.Currently,the disease is mainly controlled by vaccination with attenuated and inactivated vaccines.However,over the previous few years it was reported that the classical pseudorabies vaccines have issues of inducing poor immune response resulting in poor protective efficacy.Therefore,a clinically effective method is required to improve the immune response of these vaccines.Chinese herbal extracts such as ginseng stem-leaf saponins(GSLS)and polysaccharides of.Atractylodes macrocephala(RAMPs)have been shown to enhance the immune response of vaccines by modulating the cellular and humoral immunity in animals.In this study,combination of selenium(Se)with GSLS or RAMPs was used to observe whether it has synergistic adjuvant effect on the pseudorabies vaccine.The salient findings are as follows:1.Effect of RAMPs-Se on antibody levels induced by attenuated PrV vaccineDifferent doses of sodium selenite(Se concentrations of 0.5,1,2[ig/0.2 ml,respectively)alone or in combination with RAMPs(300μg/0.2 ml)in the form of a solution were added into an attenuated pseudorabies virus(aPrV)vaccine that was used to immunuize the ICR mice(1000 TCID5o/0.2 ml).The PrV specific gB antibody levels in serum were measured two weeks after immunization.The results showed that there was no significant difference in the levels of gB antibody produced by combination of Se and RAMPs as compared to the Se alone.It indicated that Se and RAMPs had no synergistic effect in promoting the specific antibodies produced by aPrV vaccine-induced animals.2.Effect of GSLS and Se on antibody levels induced by aPrV vaccineThe mice in the experimental group were intragastrically administered with GSLS(0.5 mg/d)for 4 consecutive days before immunization and the control group was given normal saline The mice were then immunized with aPrV vaccine dissolved in physiological saline solution(PSS)containing different doses of Se(0,1,2,3 and 4 μg/0.2 ml).The results indicated that when GSLS was administered before immunization,a higher level of specific antibodies was achieved as compared to when Se or GSLS used alone.Among the groups,the mice injected with a Se dose of 3 μg produced the highest level of antibodiesAfter administration of GSLS(0.5 mg/d)to mice for four consecutive days,mice were immunized with aPrV vaccine diluted in PSS containing Se(dose).The effect of GSLS and Se on the aPrV-induced humoral immunity was evaluated by detecting gB-specific antibody(IgG)and its subclass levels in sera of mice.The results showed that GSLS and Se significantly increased the levels of IgG,IgGl and IgG2a in the serum of animals3.Effect of GSLS and Se on cellular immunity induced by aPrV vaccineAfter administration of GSLS(0.5 mg/d)to mice for four consecutive days,mice were immunized with aPrV vaccine diluted in PSS containing Se(3μg/0.2 ml).After 24 h of immunization,the effect of GSLS and Se on early immune response was observed by detecting the activity of NK cells and the level of IFN-y in serum.Two weeks post immunization,the spleens of mice were isolated for measurement of lymphocyte proliferation and cytokine secretion levels.The results indicated that compared with the vaccine control group,GSLS and Se not only sigynificantly increased the NK cell cytolytic activity and IFN-y secretion,but also significantly enhanced the lymphocyte proliferation and level of cytokines secretion(IL-5,IL-10,IFN-y and IL-12)4.GSLS and Se improves survival rate of immunized mice after challengeICR mice were divided into aPrV vaccine group,GSLS and Se-aPrV vaccine group and blank control group.Two weeks post-immunization,the mice were challenged with an injection of a virulent field PrV(fPrV,5×105 TCID50)and the survival rate of the mice was observed and recorded for 10 consecutive days.The results showed that the blank control group manifested neurological signs after challenge and all the mice died within 4 days while the survival rate of the GSLS and Se-aPrV vaccine group was 60%,which was higher than the 30%survival of the aPrV vaccine group5.Effect of GSLS and Se on humoral immunity induced bv inactivated PrV vaccineAfter administration of GSLS(0.5 mg/d)for four consecutive days,mice were immunized twice(2 weeks apart)with inactivated PrV vaccine containing Se(3 μg/0.1 ml).The blood was collected at 2,3,and 4 weeks after booster immunization to detect the levels of PrV gB specific antibody(IgG)and its subclasses in the serum.It was indicated by the results that GSLS and Se can significantly elevate the level of gB antibody in the serum of animals,with the highest antibody level achieved at 3 weeks post-booster immunization.At the same time GSLS and Se also significantly elevated the serum IgGI and IgG2a levels6.Effect of GSLS and Se on cellular immunity induced by inactivated PrV vaccineAfter administration of GSLS(0.5 mg/d)for four consecutive days,mice were immunized twice(2 weeks apart)with inactivated PrV vaccine containing Se(3μg/0.1 ml).Four weeks after booster immunization,spleens of mice were isolated for the detection of splenic lymphocyte proliferation activity and the level of cytokines secretion.Compared to the vaccine control group,GSLS and Se significantly enhanced the proliferation of splenic lymphocytes and the secretion levels of cytokines(IFN-γ,IL-2 and IL-6)in the immunized mice.7.GSLS and Se improves survival rate of mice immunized with inactivated PrV vaccine after challengeICR mice were divided into PrV vaccine group,oral GSLS group,GSLS and Se-PrV vaccine group,and blank control group.Two weeks post-immunization,the mice were challenged with a virulent field PrV and the survival rate of the mice was observed and recorded for 10 consecutive days.The results showed that the blank group and the oral GSLS group manifested neurological signs after challenge and all the animals died within 60 h;while the survival rate of the GSLS and Se-PrV vaccine group was 70%.,higher than the 50%survival of the PrV vaccine groupIn conclusion,oral GSLS in combination with injection of Se-containing PrV vaccines synergistically promoted significantly higher immune responses in mice compared with the GSLS or Se used alone.GSLS and Se can significantly enhance the early innate immune response,and humoral and cellular immune responses induced by pseudorabies attenuated vaccine(aPrV)and the inactivated vaccine along with an increased surv ival of immunized mice after challenge with virulent fPrV.Oral administration of GSLS in combination with Se injection has a practical use and deserves further research for improving the immune response against animal vaccines.