[Antigenicity of major hydrophilic region II of hepatitis B virus surface antigen]

To study whether the substitutions at the major hydrophilic region II (MHRII) of hepatitis B surface antigen (HBsAg) will impair the antigenicity of HBsAg.

Four recombinant plasmids expressing mutant HBsAg (mtHBsAg) P1120T, C121S, K122I and T123N were constructed. HepG2 cells were transfected with the four plasmids and a plasmid expressing G145R HBsAg. The immunoreactivity of the cells expressing mtHBsAg with P1120T, C121S, K122I, T123N and G145R were detected by immunofluorescence (IF) staining and ELISA with 4 antibodies and 7 HBsAg diagnostic kits respectively.

mtHBsAg with P120T was recognized by mAb1 and mAb2. mtHBsAg with C121S and K122I was not recognized by any mAbs. mtHBsAg with T123N in lysates was recognized by mAb2, but not recognized in the supernatants.

Substitutions at amino acid positions 120-123 of HBsAg strongly impaired the antigenicity of HBsAg, a fact that was not appreciated previously.