Adaptation of hepatitis C virus for persistent infection in patients with acute hepatitis.

Nucleotide sequencing was used to analyze amino acid substitutions in the putative envelope 1 (E1) and envelope 2/nonstructural 1 (E2/NS1) regions of hepatitis C virus (HCV) to clarify a viral mechanism of persistent infection in three patients with acute hepatitis C who developed chronic hepatitis and two patients with chronic hepatitis. The HCV RNA titer in serum decreased markedly after the onset of acute hepatitis and then re-elevated. During this period, the substitution rate in the E2/NS1 region (especially in the hypervariable region located in the N-terminus) was significantly higher in patients with acute hepatitis than in patients with chronic hepatitis (P < 0.05). When patients with acute hepatitis C became persistent HCV carriers, the substitution rate decreased to the level seen in patients with chronic hepatitis. The amino acid substitution rate in the E1 region in the acute phase was similar to that found in the chronic HCV carrier state. These observations suggest that rapid substitution of the amino acid sequence in the hypervariable region of the E2/NS1 region may be one of the mechanisms of persistent HCV infection.