The Effect Of Alv-induced Immunosuppression On The Immune Protective Efficacy Of Marek’s Disease Vaccine

At present,there are three major viral neoplastic diseases including avian leukosis(AL),Marek’s disease(MD)and reticuloendotheliosis(RE)that threaten the development of the poultry industry.Epidemiological investigations show that Marek’s disease virus(MDV)was found to be the dominant causative agent of the clinical tumors before the subgroup J avian leukosis virus was introduced into Guangxi and infected the indigenous chicken breeds.Since 2014 avian leucosis virus(ALV)has gradually replaced MDV as the major pathogen of clinical tumors in Guangxi local chickens.However,in recent years,co-infection of ALV and MDV has been becoming clinically common.Therefore,it is of great significance to study this co-infection and the influence on the tumors incidence,and that is crucial to the comprehensive prevention and control of neoplastic diseases in Guangxi.In this study,we first performed the artificial embryo infection of ALV-J to evaluate the effect of ALV-J infection on the immune response to MD vaccine CVI988/Rispens of the hatching chickens.Subsequently,the ALV positive breeders were used to breed to produce the hatching offsprings of the nature vertical infection and to conduct the vaccination-challenge test to evaluate the effect of natural vertical infection of ALV on the immunoprotective efficacy of CVI988/Rispens against the challenges of vvMDV and vMDV respectively.Firstly,the 7-day-old chicken embryos were artificially inoculated with the ALV-J local isolate GX15MM6-2 by the route of yolk sac,and then the hatched chicks were raised and observed during the whole experiment until 60-day-old.The observed parameters including growth performance,antibody response levels of the vaccinated CVI988/Rispens and inactivated oil-emulsion vaccines(OEVs)Newcastle disease(ND),avian influenza virus subtype 5(AIV-H5)and subtype H9(AIV-H9),ratio of peripheral blood T lymphocytes,expression levels of IL-10 mRNA,gross pathological lesions and the histopathological changes were observed.The results showed that artificial embryo inoculated with ALV-J could induce the suppression of body-weight gain,decreased antibody responses of vaccines CVI988/Rispens and ND,AIV-H5 and AIV-H9(P<0.05),and increased the expression levels of IL-10 mRNA(P<0.05).ALV-J can reduce the proportion of CD4+T lymphocyte subsets and increase the proportion of CD8+T lymphocyte subsets,thereby reducing CD4+/CD8+.The results demonstrated that embryo infection with ALV-J could inhibit the growth of hatching birds and the immune responses of the inoculated vaccines CVI988/Rispens and ND,AIV-H5 and AIV-H9.Secondly,ALV positive male breeders × positive female breeders and negative male breedersx negative female breeders were used for crossbreeding to produce eggs and hatching offsprings.The CVI988/Rispens vaccine was used to vaccinate birds at 1-day-old.On 7 days of age,the birds were inoculated with the inactivated OEVs AIV-H5 bivalent(Re-6+Re-3)and NDV +AIV-H9 bivalent(LaSota+F).Then the birds were inoculated with the vvMDV local strains GXY2 and vMDV strains GA respectively at 15-day-old.Then the growth performance,immune organs index,inactivated vaccine antibody response,MDV viral load,clinical symptoms and histopathological changes of the experimental birds were observed,and the tumor incidence,mortality and protective index against the challenges were calculated and analyzed.The results showed that the MDV viral load of the offsprings of the ALV positive breeders was significantly higher than that of the ALV negative breeders’(P<0.05),and the mortality and tumor incidence of offsprings of the ALV positive breeders were higher than those of the ALV negative breeders’.While the vaccine protective index of the offsprings of the ALV positive breeders was lower than that of ALV negative breeders’.Both the infections of ALV and MDV could significantly inhibit the body weight gain of the birds(P<0.05),and affect the development of the immune organs.The results demonstrated that natural vertical infection ALV in chickens can cause immunosuppression,resulting in reduced immune protective efficacy of vaccine CVI988/Rispens.The results of the study demonstrated that the natural vertical infection of breeder chickens and the inoculation of chicken embryo with ALV can all induce the immunosuppression of hatching chickens and reduce the immune protective efficacy of MD vaccine.