X-ANTIGEN POLYPEPTIDES IN THE SERA OF HEPATITIS-B VIRUS-INFECTED PATIENTS

Studies were carried out to test the hypothesis that the X antigen product(s) of hepatitis B virus (HBV) appeared in serum during infection. Consequently, when serial sera from HBV-infected renal dialysis patients were tested for X antigen (HBxAg) by ELISA, many were positive. Sera from several positive patients were further characterized by immunoprecipitation followed by SDS/PAGE and Western blotting to discern the number and size of immunoreactive polypeptides. The dominant polypeptide observed in positive sera was approximately 17,000 Da (p17), which is compatible with the full-length size of the X gene product potentially encoded by HBV. Some sera contained another polypeptide species, approximately 13,000 Da (p13) in size. HBxAg was present most often in sera positive for HBeAg and/or HBV DNA or apparently complexed to anti-HBx in sera lacking these markers. Sera from HBV negative individuals were negative for these polypeptides. It appears, then, that HBxAg can be found in the serum of some HBV-infected patients as one or more polypeptide species associated with other markers of virus replication. In the presence of anti-HBx, HBxAg can be found after the peak of virus replication and may be the only detectable antigen in the blood of some chronically infected patients. © 1990.