An enzyme-linked immunosorbent assay (ELISA) has been described for serological determination
of hepatitis B virus genotypes, using monoclonal antibodies (mAb) against seven distinct
epitopes (b, m, k, s, u, f and g) on the preS2-region products of hepatitis B surface
antigen (HBsAg). The usefulness of this method for serological detection of genotype
E, however, was theoretical, because no HBsAg samples of this genotype were included
in the original test panel. Moreover, the predicted serotype of genotype E (bksufg)
closely resembled that of genotype D (bksu, bksuf or bksug). Four HBsAg samples of
genotype E were tested by the original described ELISA. The epitope g, predicted to
be present in these samples by amino acid sequences, was not detected when HBsAg of
genotype E was captured on a solid phase by mAb to the common determinant 'a' of HBsAg
and then reacted with mAb to g (5156) labeled with horseradish peroxidase. However,
the four examples of HBsAg of genotype E were captured by mAb 5156 to g on a solid
phase; they were then detected by labeled mAb to the common determinant 'a'. Since
epitopes f and g co-occurred on HBsAg of genotype E, HBsAg samples of this genotype
were also detected, by 'sandwiching' them between immobilized mAb to g and labeled
mAb to f. By contrast, HBsAg of genotype D in 90 sera was not reactive when sandwiched
between mAb to f and g. Thus, this modified ELISA enables the serological determination
of all six genotypes of HBsAg and, by inference, of hepatitis B virus.