No abstract

Hepatitis B (HB) breakthrough infections, identified by the presence of HB core (c) antibody, were found in 32 of 358 Gambian children vaccinated with plasma-derived HB vaccine. Over 2 years, 15 of these children lost their HBc antibodies. These children had significantly higher HB surface antibody levels before infection than those who retained HBc antibodies. One child, who responded well to the vaccine, had HB viral DNA detected in the presence of HBs antibodies. The S gene sequence of this DNA showed nucleotide changes that resulted in an amino acid substitution at residue 141 (lysine to glutamic acid) of the surface antigen. This finding suggests the child was infected with a variant virus that was not neutralized by antibodies resulting from HB vaccination.

The emergence of variants in the outer envelope proteins of hepatitis B virus (HBV) are found among individuals vaccinated against HBV and asymptomatic carriers of the infection. For example, children in The Gambia vaccinated against hepatitis B may show serological evidence of breakthrough infections, particularly if anti-HBs antibodies induced by the vaccine are low in titre. A single-point mutation at nucleotide 421 of the S gene is associated with such breakthrough infections. In the present study, the antigenicity of variant HBV S protein expressed as HBsAg particles in a vaccinia virus expression system has been characterised using a panel of monoclonal antibodies directed against linear and conformational determinations of the S protein. A cellular ELISA procedure using expressed antigen in Vero cells revealed differences in reactivity using four of the six antibodies that had been raised against the adw subtype of HBV and recognise conformational epitopes in the a determinant. In two instances, an enhanced reactivity for the variant antigen was found, confirming that point mutations in the a determinant of the S protein between residues 139 and 147 may result in significant changes in conformation. These findings also demonstrate that there are distinct antigenic differences between the vaccine strains of HBsAg/ adw subtype and the predominant HBsAg subtype circulating in West Africa. The implications of this work are that serodiagnosis of HBV infections may be unreliable in populations where there is a possibility of variant HBV infections emerging in the face of increasing herd immunity to HBV as a result of vaccination, particularly using monoclonal antibody-based diagnostic tests. Such variants may play a role in the maintenance of HBV infections in endemic regions.

No abstract

A novel method for the identification of hepatitis B virus (HBV) variants was developed. The ligase chain reaction (LCR) distinguished the sequences of two isolates from the Gambia showing a change at nucleotide 421 within the region coding for the surface protein a antigenic determinant. One sequence was derived from a child previously immunized with HBV vaccine, while the other, reported here for the first time, was from a chronic carrier. Nucleotide variations within the target sequence at, or up to 3 bases from the point of ligation inhibited the reaction. The LCR recognised variations in as little as 0.9 fmol DNA and will permit the rapid detection of HBV variants in molecular epidemiological studies.

A novel method for the identification of hepatitis B virus (HBV) variants was developed. The ligase chain reaction (LCR) distinguished the sequences of two isolates from the Gambia showing a change at nucleotide 421 within the region coding for the surface protein a antigenic determinant. One sequence was derived from a child previously immunized with HBV vaccine, while the other, reported here for the first time, was from a chronic carrier. Nucleotide variations within the target sequence at, or up to 3 bases from the point of ligation inhibited the reaction. The LCR recognised variations in as little as 0.9 fmol DNA and will permit the rapid detection of HBV variants in molecular epidemiological studies.