Immunity Of LaSota Attenuated Vaccine Is Suppressed By Subgroup B Avian Leukosis Virus Infection

Up to now,it has been reported many times that ALV virus exists in attenuated vaccine,which affects the immune effect of vaccine.Among them,ALV-B is still widely found in chickens in various local breeds in China.In addition,LaSota attenuated vaccine has been a vaccine widely used in poultry.To study the immune response of chickens infected with ALV-B to LaSota vaccine is of great significance for the comprehensive prevention of ND and AL diseases.By artificial simulation test,after dividing SPF chickens randomly,the experimental group was intraperitoneally injected with ALV-B and the control group was injected with normal saline at 7 days old.After 7 days,all were dripped the LaSota attenuated vaccine by nose.At 3-8w,the indexes of liver,spleen,bursa and thymus were measured.NDV antibodies,INF-γ,IL-2 cytokines and ALV-B p27 were measured by various ELISA kits after isolating serum.Peripheral blood CD4~+and CD8~+T lymphocyte were measured by flow cytometry.Finally,the ultrastructure of the virus was observed by transmission electron microscopy and the pathological sections were used to observe the histopathological changes.When there was ALV-B in LaSota vaccine,the weight of the experimental group was lower than that of the control group.The index of liver and spleen was higher than that of control group.The difference of liver index at 21 days old was significant(P<0.05),but the difference of spleen index was not significant(P>0.05).The change of thymus index was not obvious in general,and the bursal index was lower than the control group,but all the differences were not significant(P>0.05).The concentration of NDV-Ab in the experimental group was significantly lower than that in the control group,and the difference was significant at 35d,42d,and 56d(P<0.05).Concentrations of INF-γand IL-2 were lower than those in the control group.There were significant differences in INF-γat 21d,28d,and 56d(P<0.05).The level of IL-2 was significantly different except for 35d(P<0.05).The percentage of CD4~+and CD8~+in the experimental group was lower than that in the control group,the differences of CD4~+at 28d and 42d were significant(P<0.05),and the difference of CD8~+was significant at56 d(P<0.05).The p27 antigen test showed that was positive from the 3rd week,increased first and then decreased,reaching the peak at the 5th week.In the liver TEM images,lymphocyte nuclear condensation,nucleolysis,volume increase,vacuolation,fat droplets in mitochondria,and apoptosis were observed.Virions of varying sizes were also found.In the experimental group,HE pathological sections showed that lymphocyte infiltration and local necrosis were in liver,severe hemorrhage and lymphocyte hyperplasia were in spleen,bleeding spots and lymphocyte proliferation were in bursa,and lymphocyte hyperplasia was in thymus.However,they were no obvious lesions in the control group.In conclusion,the ALV-B virus can significantly reduce the effect of LaSota vaccine,and chiefly cause lymphocyte proliferation,nuclear condensation,nuclear lysis,etc.