AIM:To establish a convenient immunoassay method basedon recombinant antigen preS1(21-119aa)to detect anti-preS1antibodies and evaluate the clinical significance ofantibodies in hepatitis B.METHODS:The expression plasmid pET-28a-preSl wasconstructed,and a large quantity of preS1(21-119aa)fragment of the large HBsAg protein was obtained.ThepreS1 fragment purified by Ni~(2+)-IDA affinity chromatographywas used as coated antigen to establish the indirect EUSAbased on streptavidin-biotin system for detection of the anti-preSl antibodies in sera from HBV-infected patients.Forfollow-up study,serial sera were collected during theclinical course of 21 HBV-infected patients and anti-preSlantibodies,preS1 antigen,HBV-DNA and other serologicalHBV markers were analyzedRESULTS:preSl(21-119aa)fragment was highly expressedfrom the plasmid pET-28a-preS1 in a soluble form in E.Coli(30 mg·L~(-1)),and easily purified to high purity over 90 % byone step of Ni~(2+)-IDA-sepharose 6B affinity chromatography.The purity and antigenicity of the purified preS 1(21-119aa)protein was determined by 150 g·L~(-1)SDS-PAGE,Westernblot and a direct ELISA.Recombinant preS1(21-119aa)protein was successfully applied in the immunoassay whichcould sensitively detect the anti-preS1 antibodies in serumspecimens of acute or chronic hepatitis B patients.Resultsshowed that more than half of 19 acute hepatitis B patientsproduced anti-preS1 antibodies during recovery of thedisease,however,the response was only found in a few ofchronic patients In the clinical follow-up study of 11patients with anti-preS1 positive serological profile,HBsAgand HBV-DNA clearance occurred in 6 of 10 acute hepatitis Bpatients in 5-6 months,and seroconversion of HBeAg anddisappearance of HBV-DNA occurred in 1 chronic patientstreated with lavumidine,a antiviral agent.CONCLUSION: The high-purity preSl (21-ll9aa) coated antigen was successfully prepared by gene expression and affinity chromatography. Using this antigen, a conveniently detective system of anti preSl antibodies in sera was established. Preliminarily clinical trial the occurrence of anti-preSl antibodies in acute hepatitis B patients suggests the clearance of HBV from serum in a short-term time, and anti preSl positive in chronic patients means health improvement or recovery from the disease. AIM: To establish a convenient immunoassay method based on recombinant antigen preS1 (21-119aa) to detect anti-preS1 antibodies and evaluate the clinical significance of antibodies in hepatitis B. METHODS: The expression plasmid pET-28a-preSl wasconstructed, and a large quantity of preS1 (21-119aa) fragment of the large HBsAg protein was obtained. The preS1 fragment was purified by Ni ~ (2 +) - IDA affinity chromatography was used as coated antigen to establish the indirect EUSA based on streptavidin-biotin system for detection of the anti-preSl antibodies in sera from HBV-infected patients. For follow-up study, serial sera were collected during the clinical course of 21 HBV-infected patients and anti-preSlantibodies, preS1 antigen, HBV- DNA and other serological HBV markers were analyzedRESULTS: preSl (21-119aa) fragment was highly expressed from the plasmid pET-28a-preS1 in a soluble form in E. coli (30 mg · L -1), and easily purified to high purity over 90% by step of Ni 2+ IDA-sepharose 6B affinity chromatography .The purity and antigenicity of the purified preS 1 (21-119aa) protein was determined by 150 g · L -1 SDS-PAGE, Westernblot and a direct ELISA. Recombinant preS1 (21-119aa) protein was successfully applied in the immunoassay which can sensitively detect the anti-preS1 antibodies in serumspecimens of acute or chronic hepatitis B patients. Resultsshowed that more than half of 19 acute hepatitis B patientsproduced anti-preS1 antibodies during recovery of the disease, however, the response was found only in a few of chronic patients In the clinical follow-up study of 11patients with anti-preS1 positive serological profile, HBsAg and HBV-DNA clearance occurred in 6 of 10 acute hepatitis B patients in 5-6 months, and seroconversion of HBeAg and disappearance of HBV-DNA occurred in 1 chronic patientstated with lavumidine, an antiviral agent. CONCLUSION: The high-purity preSl (21-ll9aa) coated antigen was successfully prepared by gene expression and affinity chromatography. Using this antigen, a conveniently dPreterm intimate antibodies against sera were established. Preliminarily clinical trial the occurrence of anti-preSl antibodies in acute hepatitis B patients suggests the clearance of HBV from serum in a short-term time, and anti preSl positive in chronic patients means health improvement or recovery from the disease.