The RNAs of infective and incomplete influenza virions grown in MDBK and HeLa cells

Abstract

The MDBK line of bovine kidney cells inoculated with the WSN strain of influenza virus at high or low multiplicity produce a high yield of infective virus containing at least five distinct pieces of RNA. There is a significant decrease in infectivity and PFU HA ratio only after three or four serial undiluted passages of virus in MDBK cells, but when this decrease occurs, it is accompanied by a decrease in the largest piece of viral RNA and an increase in the amount of the small, heterogeneous RNA. HeLa cells inoculated with the WSN strain of influenza virus grown in MDBK cells produce infective virus containing at least 5 pieces of RNA similar to those in virus obtained from chick embryo and MDBK cells; however, HeLa cells inoculated with virus grown in the chick embryo produce noninfective virus with a deficiency of the largest piece of viral RNA and an increase in the amount of small, heterogeneous RNA. These results confirm the partial host cell dependence of incomplete virus formation, the loss of the largest piece of viral RNA, and the increase in the amount of small RNA in incomplete virus. They also indicate that HeLa cells can produce infective influenza virus if the inoculum is relatively free of incomplete virus, and suggest that the mechanism involved in the abortive infection of HeLa cells is similar to that involved in the von Magnus type of incomplete virus formation in other cells.