In order to elucidate the mechanism by which
HLA antigens expression is induced or enhanced on the injured or transformed hepatocytes, we have made in vitro studies using human hepatic
tumor-derived cell lines as a model system. In the present study, PLC-PRF-5 cells that have the integrated form of hepatitis B virus genome in
DNA were treated with
5-azacytidine (5-azaC) in combination with
gamma-interferon (IFN-gamma) or
dimethyl sulfoxide (
DMSO).
HLA antigens on the cell surface were quantitated by using a modified cell-ELISA method. As a result, it was demonstrated that
DMSO- or IFN-gamma-treatment enhanced expression of HLA
class I antigens on the cell surface. In addition, enhanced expression of the
antigens on PLC-PRF-5 cells treated with 5-azaC in combination with IFN-gamma or
DMSO represented a synergistic effect of these inducers on HLA
class I antigens expression although no changes in
HLA antigens expression were induced after 5-azaC-treatment alone in short-term experiments. Furthermore, an indirect immunofluorescent analysis of
hepatitis B surface antigen on the cells demonstrated increased expression of the
antigen after 5-azaC-treatment alone. HLA
class II antigens and
hepatitis B core antigen were not induced even after those treatments and also not after a long-term experiment. These results might indicate possible modulation of HLA class I and hepatitis B virus
antigens expression on the cultured cells by
a DNA hypomethylating agent, 5-azaC.