Expression Of Some Innate Immune Related Genes In Thymus Tissue Of Chickens Infected With FAdV-4

Fowl adenovirus serotype 4(FAdV-4)belongs to the avian adenovirus(Fowl adenovirus,FAV)type C,and the avian adenovirus is an adenovirus family.FAdV-4 distributed in bird flocks worldwide.FAdV-4 infection caused a huge loss to poultry industry and has been harmful to animal biosecurity around the world.In recent years,accumulate evidences about pathogenesis of FAdV-4 from domestic and foreign are mainly focus in the eye,respiratory system and digestive systems in the infected birds,however,the studies on infected immune system are limited.In this study,3-week-old white feather broiler chickens were inoculated with FAdV-4,the lesions of infected thymus and the viral load as well as the expression of innate immune related genes mRNA were detected by using HE staining and quantitative real-time RT-PCR assay,respectively.The results are as follows:1.Non-immune healthy white feather boiler chickens were experimentally inoculated with FAdV-4(103 EID50/mL),and thymus tissue was collected at indicated days post inoculation(dpi).Infected chickens did not appear obvious symptoms until 3 dpi,sudden death showed at 4 dpi,and the symptoms gradually reduced between 7 dpi to15 dpi.HE staining showed significant thymic atrophy,bleeding,and local tissue necrosis in the thymus at 4 dpi and 5 dpi,and the tissue lesions gradually reduced between 7 dpi and 15 dpi.The above results demonstrates that the FAdV-4 infected chicken model were successfully established.2.The viral load and the expression of innate immune related genes in the thymus tissue of chickens infected with FAdV-4 were detected by fluorescence quantitative RT-PCR.The results showed the viral load in the thymus was first detected at 1 dpi and peaked at 4 dpi,followed by a gradually decreased.Moreover,both the expression of TLR3/7 and MDA5 was up-regulated in thymus tissue and peaked at 4 dpi,and the levels of MDA5 expression at 4 dpi was significant increased as compared that for control groups(P<0.001).The expression levels of IL-2,IFN-? and IFN-? in thymus tissues reached peak at 4dpi,and the increased fold was 31.79,4.59,and 3.75,respectively.The levels of IL-4 and IL-10 reached peak at 3 dpi and 5 dpi,respectively,followed by a gradual decrease.Both the expression of TGF-?1 and TGF-?2 mRNA peaked at 4 dpi,and then decreased.The above results showed that the changes of innate immune related genes expression levels in FAdV-4 infected thymus were consistant with the changes of virus load in the tissues.The results in the present study demonstrate that FAdV-4 could survive and replicate in chicken thymus tissue and FAdV-4 infection can induce serious lesions in thymus tissue as well as the changes of the expression of immune-related gene mRNA in thymus tissue.This study will shed light on understanding of the pathogenesis of FAdV-4 infection on the immune organs of broiler chicken and may provide strategy for the control and treatment of FAdV-4 infection.