Reactivity of 13 in vitro expressed hepatitis B surface antigen variants in 7 commercial diagnostic assays

The primary marker of current hepatitis B infection is the surface antigen (HBsAg), however HBsAg negativity does not exclude hepatitis B viremia, HBs Ag variants can be responsible for such diagnostic failures. Here 13 differ ent HBsAg variants were cloned, variant protein produced in a mammalian exp ression system, and tested using 7 commercial HBsAg diagnostic assays. Of 1 2 variants analyzed, 6 samples displayed similar reactivity to the positive control (containing standard HBsAg sequence) in most of the assays, but 6 samples, containing various mutations throughout the entire major hydrophil ic region (MHR), showed reduced reactivity, It was found that the loss of c ysteine at amino acid (aa) 124 in 1 sample affected the secretion as well a s the reactivity of HBsAg in the expression system. Thus, not all assays ar e equally able to detect HBsAg variants, implying that, to attain an accept able level of sensitivity, the antibody repertoire of the current assays sh ould be extended.