Hepatitis B surface antigen produced by a human hepatoma cell line

Abstract

Infection with hepatitis B virus is associated with the appearance in the serum of a specific antigen, hepatitis B surface antigen (HBsAg), a serologically complex structure present on the coat of the double-shelled 42-nm hepatitis B virus (HBV) particle. HBsAg is also present, often in large excess, in the form of small, spherical 20–25-nm particles in the sera of infected individuals¹. The serologically distinct core (HBcAg) or nucleocapsid of the 42-nm virus is 27 nm in diameter and contains double-stranded circular DNA with a molecular weight (MW) of 1.6–2.0 × 10⁶, and an associated DNA polymerase². A third antigen, hepatitis B e antigen (HBeAg), appears to correlate with the number of virus particles³ and the relative degree of infectivity of surface antigen-positive sera^4, is frequently detected free in the serum and has been shown to be closely associated with the viral core⁵. Failure to propagate hepatitis B virus serially in tissue culture is a major obstacle to precise biochemical characterisation of the antigens and the development of vaccines against this important infection. The use of purified HBsAg 20–25-nm particles prepared from the sera of persistently infected donors for the immunoprophylaxis of hepatitis B is being investigated⁶. Such preparations have been shown to protect susceptible chimpanzees on challenge with HBV^7,8. There are, however, problems associated with the collection of HBsAg positive sera from persistently infected carriers. The recent establishment of a HBsAg-producing cell line from a human hepatoma^9,10 has provided an alternative source of HBsAg particles with the added advantage that both the production and quality of the antigen may be more precisely controlled. The availability of this cell line also facilitates the study of HBV gene products by biochemical methods applicable to cultured cells, in the absence of contaminating serum proteins. In this study, the 20–25-nm HBsAg particles produced by these cells were characterised and compared with those derived from the sera of persistently infected human carriers.