The Molecular Mechanism Of Infection Of Newcastle Disease Virus From Different Hosts On The Immune Function Of Chickens

Newcastle disease(ND) is a highly pathogenic viral disease of the chicken caused by Newcastle disease Virus(NDV), which remains a constant threat to poultry productors worldwide. There are multiple genotypes of NDV. The immune protective efficacy of conventional vaccine is not ideal. Furthermore, developing new vaccine is always lagging behind the pathogenic changes. It is urgent to improve the immune function of birds and find novel control strategies to combat infections to innate immunity. Avian β-defensins(Av BDs) are cationic cystine-rich antimicrobial peptides.They display a wide range of microbicidal or microbiostatic activities against bacteria, viruses, fungi and play an important role in the innate immune system.In order to investigate whether the m RNA expression of chicken Av BDs was constitutive or inducible in response to NDV infection, and its signal transduction mechanism of antiviral effect, thirty SPF chickens were randomly divided into three groups with 10 birds per group. The two infected groups were infected orally with either of chicken originated NDV(F48E9), or duck originated NDV(Md/CH/LGD/1/2005)(Md). The levels of the m RNA, including NDV, 18 s RNA, Av BD 1-13, toll-like receptors(TLRs), My D88, IRF7 and cytokines in tissues from the control or both infected groups, were examined by the real-time RT-PCR method. The results showed that the level of m RNA expression of Av BD2, 3, 4, 5, 6, 9 and 10 were up-regulated in most of tissues of chicken infected with both originated NDVs. The m RNA of Av BD2 showed significantly up-regulated in kidney of chicken infected with Md on 48 h post infection(hpi)(P<0.05). The m RNA of Av BD5 showed significantly up-regulated in lungs of chicken infected with Md on 48 hpi(P<0.05).The result indicated that these Av BDs can be induced by NDV. The level of m RNA expressions of TLR2, 3, 4, 7 were up-regulated in all of tissues of chicken infected with both NDVs, and significantly up-regulated in lungs of chicken infected with Md on 48 hpi(P<0.05). The level of m RNA expression of My D88 was up-regulated in all of tissues of chicken infected with both NDVs. However, little obvious change was found on the m RNA expression of IRF-7 and IFN-β. The m RNA expression of IL-8、IFN-γ were up-regulated in kidney of chicken infected with Md on 48 hpi(P<0.05). The m RNA expression of IFN-γ showed down-regulation in kidney of Md infected chicken on 24 hpi(P < 0.05). The m RNA expression of MHC class II showed down-regulation in kidney of Md infected chicken on both 24 and 48hpi(P<0.05). These results indicated that chicken may induce Av BD2, 5, IL-8, IFN- γ and MHC class II through TLR2, 3, 4, 7 mediated signal transduction pathways to protect these tissues from microbial.In order to investigate whether Av BDs potent direct antiviral activity aginst NDV in vitro, Av BD2 was chosen for further study on antiviral activity against NDV, based on the level of m RNA expression of Av BDs in chickens infected with NDV. The results showed that the recombinant protein have little obvious antiviral activity against NDV in vitro, needing to further study.In summary, The levels of m RNA expression of Av BD2, 5 were significantly upregulated in chickens infected with NDV. Chicken may induced Av BD2, 5, IL-8, IFN-γand MHC class II by TLR2, 3, 4, 7 mediated signal transduction pathways.