Use of monoclonal antibodies to determine if HBsAg of mixed subtype is one particle or two.

Of the ten universally recognized subtypes of hepatitis B surface antigens, two contain both of what are normally mutually exclusive subtype determinants. These mixed subtypes presumably result from a concurrent infection by different viral subtypes and result in the presence of the various subtypes either on separate particles or intermixed on one particle. This study demonstrates that both of these alternatives can occur. Additionally, a mixed subtype present on one particle could result from either intermixing of separate protein subtypes into the same viral envelope (phenotypic mixing) or genetic recombination between viruses of different subtypes resulting in the production of one protein with a mixed subtype (genotypic mixing). The latter possibility would make the definition of the antigenic determinants and production of a vaccine for hepatitis B more difficult since it implies that the virus can alter its surface characteristics. Evidence is provided against genotypic mixing, demonstrating that phenotypic mixing does occur but does not 'breed true' upon viral transmission.