Growth of hepatitis A virus in a mouse liver cell line.

Hepatitis A virus (HAV) has been adapted to grow efficiently in primate and some nonprimate cell lines but not in cells of murine origin. To understand the inability of the virus to grow in mouse cells, we studied the replication of HAV in immortalized and nontransformed MMH-D3 mouse liver cells, which require growth factors and collagen to maintain their phenotype. HAV grew in MMH-D3 cells transfected with virion RNA but not in those infected with viral particles, indicating a cell entry block for HAV. However, MMH-D3 cells cultured under suboptimal conditions in the absence of growth factors acquired susceptibility to HAV infection. Serial passages of the virus in MMH-D3 cells under suboptimal growth conditions resulted in the selection of HAV variants that grew efficiently in MMH-D3 cells cultured under both optimal and suboptimal conditions. Nucleotide sequence analysis of the MMH-D3 cell-adapted HAV revealed that N1237D and D2132G substitutions were present in the capsid regions of six viral clones. These two mutations are most likely located on the surface of the virion and may play a role in the entry of HAV into the mouse liver cells. Our results demonstrate that mouse hepatocyte-like cells code for all factors required for the efficient growth of HAV in cell culture.