Antibody to hepatitis B virus core antigen (anti-HBc) is one of the most important serological markers during hepatitis B virus (HBV) infection. The quality of the hepatitis B virus core antigen (HBcAg; diagnostic antigen) is crucial to the accuracy of anti-HBc detection. In an attempt to explore the suitability of recombinant HBcAg (rHBcAg) for diagnostic purposes, HBcAg was expressed in Escherichia coli (E coli) and Pichia pastoris (P. pastoris) and evaluated for the detection of anti-H Bc. The expression level of the recombinant protein satisfied the criteria for large-scale biologic production. P. pastoris- and E coli-derived rHBcAg were purified with gel filtration followed by sucrose gradient (reagents A and C) or with a monoclonal anti-HBc antibody binding (reagents B and D) and were utilized to detect anti-HBc in competitive inhibition enzyme-linked immunosorbent assay (ELISA) format. The ELISA using P. pastoris-derived rHBcAg had a higher specificity and sensitivity than that using Ecoli-derived rHBcAg to detect the anti-HBc standard panel. Serum specimens were collected from HBV-infected patients and healthy individuals (voluntary blood donors). Anti-HBc was detected in those specimens using P. pastoris- and E coli-derived rHBcAg. The positive rate of anti-HBc detection in HBV-infected patients' sera was 100% with reagents A and B, 96.4% with reagent C, and 93.6% with reagent D. The negative rate in healthy control sera was 100% with reagents A and B, 97.0% with reagent C, and 99.7% with reagent D. These data indicate that P. pastoris-derived rHBcAg is superior to E.coli-derived rHBcAg for the detection of anti-HBc using the diagnostic ELISA. (C) 2007 Elsevier Inc. All rights reserved.