Propagation of Hepatitis A Virus in Hybrid Liver Cell Lines

Preferential growth of HAV （hepatitis A vivus ）in the primate liver tissue is already known. To obtain established cell lines with a high susceptibility to HAV, marmoset liver cells were fused with CHO （Chinese hamster ovary） or Vero （a derivative of African green monkey kidney cells）cells by a cell fusion technique with polyethylene glycol. The experiment yielded 6 hybrid cell lines（C.ja/CHO－1 to －6）between the liver and CHO cells, and 4 cell lines （S.la/Ve－1 to －4）between the liver and Vero cells. Hybrid cell lines obtained were assessed for their susceptibility by inoculating two sources of HAV, one from an infected marmoset liver tissue（liver tissue virus）and another from a fecal specimen of patient, where the virus growth was monitored by RIA （radioimmunoassy）and IFA （immunofluorescent antibody technique）, giving the following results. 1）Of 6 hybrid cell lines comprising the liver and CHO cells, three （C.ja/CHO－1, －3, and －4）were subjected to the HAV infection with the fecal virus, whereby two （C.ja/CHO－3, －4） of them were found to develop significant activities of the viral antigen transiently at 10 to 12th passages of cells. 2）Of 4 hybrid cell lines comprising the liver and Vero cells, three（S.la/Ve－1, －3, and －4）were equally susceptible te HAV, giving maximal activities of the viral antigen at 6 to 8 weeks post infection （pi） with the liver tissue virus and at 10 to 12 weeks pi with the fecal virus. 3）In S.la/Ve－1 cells, a representative of the susceptible hybrid cell lines, passage of HAV was commenced with a ten fold concentrate of the liver tissue virus, resulting in the development of plateau level activities of the viral antigen at 4 weeks pi at the initial passage and at 1 week pi after the 6th passage consistently. 4）HAV－infected S.la/Ve－1 cells did not develop CPE （cytopathic effect） and could be subcultured in an equal efficiency to that of the uninfected counterparts, retaining the maximal growth of HAV. 5）In S.la/Ve－1 cells, the cell culture-adapted HAV grew to the plateau level at 7 days pi giving an infectivity of 10^<8.5>TCID_<50>/ml, where the virus particles were confirmed in the cellular extracts in abundance by the immune electron microscopy. Taken these findings together, S.la/Ve－1, －3, and －4 cells were considered to be well susceptible to HAV and quite useful in the basic and clinical studies of HAV