Expression and immunological evaluation of the Escherichia coli-derived hepatitis C virus envelope EI protein

Immunological response against envelope protein El is very important in natural hepatitis C virus (HCV) infection, although it is insufficient to clear the viraemia, The HCV genomic region encoding the first 149 amino acids of the envelope EI protein (EI340, amino acids 192-340) was expressed in Escherichia coli (to a level of 30% of the whole cellular proteins) and purified to 85%, We measured the immune response in rabbits and mice as well as the reactivity against 37 human sera raised against the whole recombinant protein and EI-encoding peptides, From this, 51.1 % of human sera were found to react with EI340. High-level antibodies against EI340 were obtained in rabbits and mice when immunized. These antibodies had a similar peptide-recognition pattern to that described previously for human sera. The most reactive region was located at the N-terminus of the EI protein. Cellular immunity in mice was evaluated by delayed-type hypersensitivity assay. It revealed the induction of a CD4+ T-cell-mediated response by this protein. This EI340 protein and the animal-derived anti-EI sera are immunological tools that could aid in the monitoring and development of anti-HCV therapies.