ALV-j-induced Regulation Of Cytokine Gene Expressions And The Mechanism And Effect Of The Promotion Of Interleukin 6

Subgroup J Avian Leukosis, induced by subgroup J avian leukosis virus, is an infectious disease which could lead to myelocytome and other malignancies. It is also an important immunosuppressive disease for poultries. Until now, there have been many studies about ALV-J pathogenicity, most of which were done by analyzing the replication capability and pathogenicity of the viruses but ignoring the functions of the host immune system. Some studies have revealed that viruses could make use of host immune system to accomplish their pathogenicity. Cytokine is a kind of small soluble protein that is produced by various kinds of cells stimulated by immunogen, mitogen or other immunostimulant. It is able to regulate innate immunity and acquired immunity, to adjust cell growth and differentiation, to promote hematopoiesis and to repair damaged tissues. The present study aimed to reveal the oncogenous mechanism of ALV-J from the aspect of host immune system by exploring cytokine expression after ALV-J infection.This study constructed the infected model of ALV-J firstly. We tested the cytokine(IL-6, IL-18, IFN-α and IFN-γ) expressions in immune organs(spleen, bursa of Fabricius and cecal tonsil) of both the infected group and the control group and compare the expression differences between them. We also testd the virus load in the peripheral blood lymphocytes of the infected group. Both of them were measured by real time RT-PCR/PCR at 2,3,4,5,6,7,9,12,15,18 and 21 days post-infection. The results showed that all the cytokine expressions tested(including IL-6, IL-18, IFN-α and IFN-γ) were upregulated together with the increase of the ALV-J load in the hosts after ALV-J infection. And when ALV-J load got its peak, cytokine expressions suddenly decreased. Such phenomenon suggested that the cytokine expressions in the hosts were associated with ALV-J infection.IL-6 is an important multifunctional cytokine which would regulate the expression of other cytokines and plays a central role in the work of cytokines. IL-6 is an important immunity substance. Previous studies have showed that IL-6 is associated with tumorigenesis. As ALV-J is an important immunosuppressive disease among flocks, this study also did some researches on the mechanisms that ALV-J induced the expression of IL-6. The results showed that in the splenocytes, peripheral blood lymphocytes and vascular endothelial cells cultivated in vitro, ALV-J could induced the expression of IL-6 as it could in vivo. Further studies showed that in the splenocytes, it was the capsid p27 protein that ALV-J used to induce the expression of IL-6 and this effect was in dose-dependent manner to some extent. Also, the signaling inhibitors assays indicated that this process was dependent on the activation of PI3 K and NF-κB cell signal transductive pathways. Dual-glo Luciferase assay indicated that the effect that ALV-J activated NF-κB cell signal transductive pathway would be reduced obviously when PI3 K was inhibited. This was to say that the ALV-J-induced NF-κB cell signal transductive pathway activation was dependent on the activation of PI3 K, to a great extent. In conclusion, ALV-J induced IL-6 expression with p27 protein via the activation of PI3 K and NF-κB signaling pathway.In order to reveal the tumorigenic mechanism of ALV-J on the aspect of host immune system, and study the influence of IL-6 on ALV-J tumorigenesis, this research measured the influence of IL-6 on the expressions of vascular endothelial growth factor-A(VEGF-A) and it receptor(VEGFR-2) in vivo and in vitro. The results proved that IL-6 could successfully upregulate the expression of VEGF-A and VEGFR-2 both in vivo and in vitro in vascular endothelial cells via the activation of STAT3 signaling pathway. ALV-J infection led to the overexpression of VEGF-A and VEGFR-2, and further si RNA interference assays showed that when IL-6 expression was inhibited, ALV-J could not upregulate VEGF-A and VEGFR-2 expressions. These results suggested that ALV-J promoted the expressions of VEGF-A and VEGFR-2 via its upregulation on IL-6. VEGF-A and VEGFR-2 were important substances in promoting vascular endothelial cells proliferation and vascular permeability, playing a significant role in angiogenesis. In all, ALV-J promoted VEGF-A and VEGFR-2 expression via IL-6, leading to angiogenesis and even tumorigenesis.The present study, to some extent, revealed the tumorigenesis of ALV-J from the aspect of host immune system for the first time and showed that ALV-J accomplished its pathogenesis through a hijack on host immune system. This is significant for the research on ALV-J pathogenicity and provides a new thought for such studies.