Multiplication of human rotavirus in cultured cells: an electron microscopic study

Human rotaviruses were capable of efficient multiplication in LLC-MK2 cells when the inoculum was pre-treated with trypsin, centrifuged on to the cell monolayer and the infected cells maintained in a medium containing trypsin. However, not all of the human rotavirus isolates used to infect cells resulted in efficient virus production. The ability of human isolates to multiply in cultured cells was studied by direct observation of virus in the electron microscope, by radioactive labelling with 3H-uridine of the newly synthesized virus and by electron microscopic examination of thin sectioned infected cells. With one of the specimens used (F-617) only 5 to 10% of the cells showed evidence of virus multiplication, with the great majority of the infected cells showing numerous complete (double-capsid) virus particles scattered in the cytoplasm. When cells were inoculated with another human specimen (SIB-I), infected cells were more abundant, reaching a maximum of 60%; however, a variety of particle types, probably representing different subviral structures or different steps of rotavirus morphogenesis, were commonly observed. The presence of these aberrant or incomplete virus structures may represent a manifestation of the defectiveness of this virus and may explain the difficulties encountered in its serial passage.