Protection Of Chickens Against Avian Hepatitis E Virus Infection By Immunizing With ORF3Protein

Avian Hepatitis E virus (HEV) was isolated from chickens with hepatis-splenomegaly(HS) syndrome or big liver and spleen disease (BLS) in Unied States in2001. Avian HEV ismainly responsible for hepatitis-splenomegaly syndrome, the broiler breeder hens and layinghens of30-72weeks of age, which showed reduce in egg production, regressive ovaries, redfluid in the abdomen and enlarged liver and spleen.The full lengthof avian HEV genome is approximately6.6kb, consistingof threeopen-reading frames (ORFs) and two noncodingregions. The first ORF (ORF1) encodes anon-structuralprotein with multiple functional domains, ORF2encodes thecapsid protein andORF3that overlaps with the geneORF2encodes a small phosphoprotein. Functional study onORF3has always been relatively less than ORF2which encodes the capsid protein containingmultiple epitopes and becomes the key point of vaccine study. However, in recent years it hasbeen found that ORF3plays an important role in the aspects of assembling and releasing ofvirion, cell signal transduction, cytoskeleton assembly, and In addition, it contains epitopeswhich may inducing strongly immune responses in inoculated annimals.This study adopted Escherichia coli prokaryotic expression system to express and purifythe avian HEV ORF3protein, obtained the highly purified ORF3protein, and its antigenicitywas good while the antigenicity analyzing. Subsequently, the purified complete ORF3proteinwas used as the antigen to immunize the specific-pathogen-free (SPF) broiler chickens of8weeksage, meanwhile set the control group (immunize PBS). At14day post immunizationafter the second immunization, twogroup consisting of28chickens waschallenged withCaHEV stock containing104GE/ml by i.v. After challenged,serum samples, fecal swabmaterials, liver and spleen and bile tissues of chickens were collected in different days afterchallenge. Result of the serum antibodiestiters detection before challenging shown that, thechickens after immunization of ORF3protein，produced high levels of antibodies. And serumantibodies levels of the immunized chickens after serum conversion were obviously lowerthan the control group. The fecal virus shedding detection through virus RNA in fecal samplesshowed that the number of chickens releasing virus had also declined obviously.36%ofimmunized chickens were detected with virus RNA compared to79%of the control group in the virus RNA detection of liver and spleen tissues and bile samples. The severity that theimmunized group displays the viremia is lower than the control group, moreover, the numberof chickens that had lesions on livers is significantly lower than the control group. The resultsshowed that avian HEV ORF3protein has partial effect on protection for the immunizedchickens. Results of this study laid the foundation for study of using ORF3protein as a geneengineering vaccine to prevent HEV infection.