Recombinant subunit ORF2.1 antigen and induction of antibody against immunodominant epitopes in the hepatitis E virus capsid protein

A recombinant subunit antigen (ORF2.1), representing the carboxy-terminal 2 67 amino acids of the 660-amino-acid hepatitis E virus (HEV) capsid protein , was expressed in Escherichia coli and used for the immunisation of rats. Purified antigen formulated with either Aluminium Hydroxide Gel Adjuvant (A lum) or Titermax gave high and equivalent levels of antibody after three do ses. Responses to two doses of 15, 75, or 150 mu g antigen, formulated with Alum and given at 0 and 4 weeks, were also equivalent by 17 weeks after im munisation. Rats initially developed antibody to a wide range of linear epi topes in the ORF2.1 region, but by 27 weeks the predominant response detect ed by Western immunoblotting was restricted to the conformational epitope u nique to ORF2.1 [Li et al. (1997) Journal of Medical Virology 52:289-300], a pattern that was also observed when comparing acute-phase patient serum s amples with serum samples from convalescing patients. Antibody from immunis ed rats blocked the majority of patients' serum reactivity in enzyme-linked immunosorbent assay against both ORF2.1 (57-92% inhibition) and virus-like particles of HEV produced using the baculovirus system (74-97% inhibition) . Together, these results suggest that the ORF2.1 subunit vaccine induces a n antibody response against immunodominant, conformational epitopes in the viral capsid, which largely mimics that seen in convalescent patients, who are presumed to be immune to HEV infection. J. Med. Virol. 60:379-386, 2000 . (C) 2000 Wiley-Liss.