Expression of the amino-terminal half of the NS1 region of the hepatitis C virus genome and detection of an antibody to the expressed protein in patients with liver diseases.

A cDNA fragment encompassing the 5'-terminal half of the NS1 region of the hepatitis C virus (HCV) genome was cloned. The cDNA was expressed in insect cells using a recombinant baculovirus, and a protein band of approximately 21K was identified by immunoblotting with a serum sample from a patient with chronic hepatitis C. Antibody to the protein was detected in sera from 13.4% of patients with chronic non-A, non-B hepatitis (NANBH), 20.8% of patients with liver cirrhosis and 16.8% of patients with hepatocellular carcinoma with no serum markers for hepatitis B virus infection. However, the antibody was not detected in sera from patients with acute NANBH. The prevalence of antibody to the protein encoded by the NS1 region was lower than that of antibody to the HCV core protein, but much higher than that of antibody to the envelope protein. Thus, the NS1 region of the HCV genome is suggested to encode a protein produced during the course of HCV replication.