Secretion of polyalbumin receptors in vitro

The nature of hepatitis B surface antigen (HBsAg)‐associated receptors for polymerized human serum albumin (pHSA‐R) and their relationship to hepatitis B e antigen (HBeAg) and human serum proteins have not been defined. We studied by radioimmunoassay and by electron microscopy HBsAg‐associated pHSA‐R secreted in vitro by a human hepatocellular carcinoma cell line (PLC/PRF/5) and by mouse 3T3 fibroblasts after transfection with cloned hepatitis B virus (HBV) DNA (4.10 cells). PLC/PRF/5 cells expressed only HBsAg, whereas 4.10 cells secreted also HBeAg. There was no significant difference in the production of HBsAg, HBeAg, and pHSA‐R when the cells were cultured in the presence or absence of fetal calf serum. Secretion of pHSA‐R by the two cell lines for a given amount of HBsAg was equal irrespective of the presence or absence of HBeAg. Supernatants from both cell lines grown in serum‐free medium did not contain any Clq or albumin when tested by immunodiffusion. The ability of a transfected mouse cell line to produce HBsAg with pHSA‐R activity strongly suggests that pHSA‐R is coded by the HBV genome and does not depend on the presence of human serum proteins. In addition, our findings fail to demonstrate any correlation between HBeAg production and pHSA‐R.