EFFICIENT CLASS-II MAJOR HISTOCOMPATIBILITY COMPLEX PRESENTATION OF ENDOGENOUSLY SYNTHESIZED HEPATITIS-C VIRUS CORE PROTEIN BY EPSTEIN-BARRVIRUS-TRANSFORMED B-LYMPHOBLASTOID CELL-LINES TO CD4(-CELLS() T)

The induction of an efficient CD4(+) T-cell response against hepatitis C virus (HCV) is critical for control of the chronicity of HCV infect ion. The ability of HCV structural protein endogenously expressed in a n antigen-presenting cell (APC) to be presented by class II major hist ocompatibility complex molecules to CD4(+) T cells was investigated by in vitro culture analyses using HCV core-specific T-cell lines and au tologous Epstein-Barr virus-transformed B-lymphoblastoid cell lines (B -LCLs) expressing structural HCV antigens. The T- and B-cell lines wer e generated from peripheral blood mononuclear cells derived from HCV-i nfected patients. Expression and intracellular localization of care pr otein in transfected cells were determined by immunoblotting and immun ofluorescence. By stimulation with autologous B-LCLs expressing viral antigens, strong T-cell proliferative responses were induced in two of three patients, while no substantial stimulatory effects were produce d by B-LCLs expressing a control protein (chloramphenicol acetyltransf erase) or by B-LCLs alone. The results showed that transfected B cells presented mainly endogenously synthesized core peptides. Presentation of secreted antigens from adjacent antigen-expressing tells was not e nough to stimulate a core-specific T-cell response. Only weak T-cell p roliferative responses were generated by stimulation with B-LCLs that had been pulsed beforehand with at least a 10-fold-higher amount of tr ansfected COS cells in the form of cell lysate, suggesting that presen tation of antigens released from dead cells in the B-LCL cultures had a minimal role. Titrating numbers of APCs, we showed that as few as 10 (4) transfected B-LCL APCs were sufficient to stimulate T cells. This presentation pathway was found to be leupeptin sensitive, and it can b e blocked by antibody to HLA class II (DR). In addition, expression of a costimulatory signal by B7/BB1 on B cells was essential for T-cell activation.