Quantitative Interactions of Feline Leukaemia Virus and Its Pseudotype of Murine Sarcoma Virus in Cat Cells: Requirement for DNA Synthesis

Abstract

Feline leukaemia virus and the feline leukaemia virus pseudotype of murine sarcoma (MSV(FeLV)) readily propagate in cat embryo cells. Feline leukaemia virus will rapidly attain high titres even if minimal virus inocula are used initially, and undiminished virus production will be maintained in the chronically infected cells. Feline leukaemia virus, which was previously quantitated as helper activity for defective MSV (FeLV), has now been related to the amount of autonomously replicating feline leukaemia virus. Rapid growth of MSV (FeLV) to high titre is obtained only if each sarcoma infected cell also becomes the recipient of a replicating unit of feline leukaemia virus. Conditions approximating one-step growth curves for both feline leukaemia virus alone and MSV (FeLV)-feline leukaemia virus complex can be achieved and show that first cycles of growth are completed within about 40 and 30 hr, respectively. The rate of growth of the sarcoma-leukaemia virus complex is somewhat faster than that of leukaemia virus by itself, which can result in ratios of replicating leukaemia to sarcoma viruses of less than unity. Inhibition of DNA synthesis during the first 12 hr after infection with either virus prevents virus replication. The requirement for DNA synthesis is not seen beyond the first 12 hr after infection. No stimulation of DNA synthesis is discernible after either feline leukaemia virus or MSV (FeLV) inoculation at any time after infection.