| Epidemiological survey has revealed that genotype Ⅶd NDV is dominant in many countries in Asia and Africa. Even though conventional vaccines (La Sota) can reduce mortality and morbidity of the poultry flock, while vaccinated chickens can still be infected with genotype Ⅶd virus, resulting in damages of the lymphoid tissues. However, the underlining mechanism of this pathological manifestation caused by genotype Ⅶd NDV in the vaccinated chickens remains largely unknown. In this study, the La Sota vaccinated chickens were infected with genotype Ⅶd NDV strains JS5/05 and earlier genotype Ⅸ NDV strains F48E8, respectively, and then the pathology, virus replication, the population of lymphocytes and cytokine response in lymphoid tissues were compared. In addition, to evaluate the effects of the lesions in the lymphoid tissues from the vaccinated chickens, the chickens with 6 logs HI titers against the NDV were infected with the strains JS5/05. Five days post-infection, these chickens were immunized with live vaccine (IBD) and inactivated vaccine (AI), respectively. Subsequently, the titers of specific antibodies induced by the two vaccines were detected and compared every week, respectively, between the treatment and control groups.1. The mechanism of the pathology of the immunolymphoid organs in the La Sota vaccinated chickens caused by genotype Ⅶd NDV6-week-old specific pathogen free (SPF) chickens with HI titer of 6 log2 were divided into 2 groups and challenged with JS5/05 or F48E8. Liver, spleen, lung, kidney, thymus, bursa, and duodenum were taken for pathology study and virus replication at 3,5, and 7 day post-infection (dpi). The pathology observation showed that the pathlological changes in immune tissues from JS5/05-infected chickens were more severe than those from the F48E8-infected groups. In brief, JS5/05 manifested very pathognomonic features with swollen spleen and petechiae thymus. Microscopically, the spleen and thymus from the JS5/05-infected chickens exhibited necrosis and lymphocyte depletion in the periarterial lymphatic sheath. The lesions in the bursa was characterized by the infiltration of neutrophil. However, no obvious lesions were observed in the F48E8-infected groups. Moreover, JS5/05 replicated at significantly higher levels in immune organs than F48E8 (P<0.05).Therefore, we compared the profiles of T cell and immune-related cytokines levels in spleen, thymus, and bursa after infected with JS5/05 and F48E8. Flow cytometric analysis of T cell subpopulations revealed a significant increase in CD8+T lymphocyte subpopulation(P<0.05) and a reduction in both CD4+T lymphocyte subpopulation and the ratio of CD4+/CD8+ were detected in the JS5/05-infected spleen and thymus at 7 days post-infection (P<0.05).The gene expression profiles showed a significant up-regulation of IL-1β、IL-2、 IL-6、IL-10、IFN-β、IFN-γ and LITAF in JS5/05-infected groups than those in F48E8-infected groups at 3,5, and 7 dpi(P<0.05). These results indicate that genotype Ⅷd NDV JS5/05 possessed higher ability to exacerbate inflammatory response and suppress the host cell-mediated immunity response.Our results suggest that the high replication and the the intense inflammatory response contribute to the severe tissue damage in immune organs caused by genotype Ⅶd NDV.2. Immuno-effect of genotype Ⅶd NDV infection on antibody responses to different vaccines in the La Sota vaccinated chickens5-week-old SPF chickens with HI titer of 6 log2 against the NDV were challenged with JS5/05 and then immunized with live vaccines (IBD) and inactivated vaccine (AI) at 6 weeks old, respectively. Antibody titers were detected at 0,1,2 and 3 weeks post-vaccination (pv), with ELISA for detection of antibody titer against IBDV and HI test for that against AIV. The result showed that antibody titer against IBDV or AIV in JS5/05-infected chickens was lower than that in the control group pv, respectively. The HI antibody titers against AIV in JS5/05-infected group were lower than those in the control group during the whole experiment. Significant difference in the HI titer was present between the chllange-vaccinated group (5.50±0.58 log2) and the control group (6.75±0.96 log2) at 2 weeks pv (P<0.05). The antibody titers against IBDV in JS5/05-infected group were 459.03±1036.04,5133.13±1071.97 and 3868.62±960.95 respectively, at 1,2 and 3 weeks pv, while these in the control group were 2015.91±1792.24,7547.81±1012.38 and 7137.09±1526.90. The analysis showed significant difference in antibody titer between the experimental group and the control group at 1 week pv (P<0.05) and extremely significant difference between these groups at 2 and 3 weeks pv (P<0.01). The above results indicated that the genotype Ⅶd NDV-infection in the ND vaccinated chickens could induce immunosuppression and generate negative impact on the immune efficacy from the subsequent vaccination, especially for the live vaccines. |
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