Exploration of Respiratory Tract Response Patterns in Chickens Infected with H9N2 Subtype Avian Influenza Virus
[Objective]This study was conducted to establish a model of upper respiratory tract inflammation in chickens infected with H9N2 subtype Avian influenza virus(AIV)and explore the inflammatory response caused by its infection.[Method]H9N2 subtype AIV epidemic strain GD10142 was infected with SPF chickens by nose and eye drops at a dose of 100 μL/bird(108 EID5o/100 μL).The clinical characteristics of chickens were observed after infection,and throat swabs and serum samples were collected at 0,1,3,5,7 and 9 days after infection.The pathological changes of respiratory tract and lung were observed 5 and 9 days after infection,and tracheal lavage fluid,trachea and lung tissues were collected.The viral load in throat swab,trachea lavage fluid,trachea and lung tissue was detected by Real-time quantitative PCR.The changes of serum total IgG and H9N2 subtype AIV-specific IgG were detected by ELISA,and the neutralization activity of antiserum was analyzed by serum neutralization test.The levels of inflammation-related cytokines interleukin-6(IL-6),IL-10,IL-1β,tumor necrosis factor a(TNF-a)and nuclear transcription factor κB(NF-κB)in serum and trachea lavage fluid were detected by ELISA.[Result]After infection with H9N2 subtype AIV,chickens did not show typical clinical features,but viral nucleic acid could be detected in throat swabs 1-5 days after infection,and the viral load was highest 3 days after infection,and no viral nucleic acid could be detected 5 days after infection.After 5 days of infection,viral nucleic acid was detected in trachea lavage fluid,trachea and lung,and the first two viral nucleic acid loads were higher than those in lung.The total serum IgG and H9N2 subtype AIV-specific IgG increased 3 days after infection,maintained at high levels 5-9 days after infection,and exhibited strong virus neutralizing activity.IL-10,IL-1β,TNF-α and NF-κB in serum also showed an upward trend starting from 3 days after infection,however,the contens of IL-6,IL-10,IL-1β,TNF-α and NF-κB in tracheal lavage fluid were very low,and there was no significant change before and after infection.[Conclusion]In this study,the respiratory tract model of chickens infected with H9N2 subtype AIV was successfully established,and the upper respiratory tract was determined to be the main site of infection and proliferation of H9N2 subtype AIV.The infection of H9N2 subtype AIV induced the production of pro-inflammatory and anti-inflammatory cytokines,which might be an important factor in the maintenance of immune homeostasis in infected animals.This study laid a foundation for further exploring the pathogenic mechanism and host defense mechanism of H9N2 subtype AIV.
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