Structural and nonstructural regions of the HCV-encoded
polyprotein have been expressed in recombinant yeast, bacteria, or insect cells and used to capture and measure reactive
antibodies circulating in different individuals. The putative
nucleocapsid protein (C) and nonstructural
proteins 3-5 (NS3-NS5) were found to contain the most
immunodominant epitopes. The NS3, NS4, and C regions were expressed in yeast in the form of a fused, chimeric
polyprotein (C25) and a capture assay for reactive antibody was developed. This anti-C25 assay detects all previously identified HCV-seropositive cases and provides a substantially more sensitive diagnostic for both acute and chronic HCV
infections than the current
anti-C100-3 (NS4) assay. Anti-C25 was detected more frequently than
anti-C100-3 in chronic, transfusion-associated non-A, non-B
hepatitis patients from the United States (95% vs. 71%) and Japan (98% vs. 82%), in
cryptogenic cirrhosis patients from the United States (62% vs. 28%), and in
hepatitis B surface antigen-negative cases of
hepatocellular carcinoma from Japan (83% vs. 63%). These data indicate that HCV has a greater role in these
liver diseases than was previously thought. In volunteer United States blood donors sampled following the introduction of
anti-C100-3 screening, the prevalence of anti-C25 and
anti-C100-3 was 0.5% and 0.08%, respectively.