A study of the binding ability of pre-S1 and S2 proteins of hepatitis B virus to human serum albumin.

To assess the relationship between pre-S proteins of HBV and polymerized human serum albumin (PHSA), a labeled avidin biotin ELISA was used to detect pre-S1, S2 and PHSA receptor (PHSAR) activity. PHSAR activity was only present in the samples positive for pre-S1 and/or S2, but not in the samples positive only for HBsAg. Pre-S1, S2 and PHSAR could in some degree be blocked by preincubating serum with PHSA, and the blocking efficiency of PHSA with respect to pre-S2 and PHSAR was similar, suggesting that pre-S2 is the dominant site for binding PHSA in vitro. We also found that PHSAR activity was detectable in 2 cases positive only for pre-S1, but not pre-S2. Furthermore, PHSA could selectively block pre-S1 and PHSAR activity in 2 cases negative for pre-S2, revealing that pre-S1 also possesses binding ability to PHSA, at least in a small number of cases. Using sandwich ELISA, we demonstrated the existence of complexes of HBV envelope proteins and human serum albumin (HSA) in some HBV infected serum samples. The possible significance of these complexes is discussed.