Study on the mechanism of interference between Friend leukemia and Sindbis viruses in tissue culture

Some mechanisms of interference developing in BALB/c mouse embryo fibroblast culture (MEC) infected with Friend leukemia virus (FLV) and 48 hours later superinfected with Sindbis virus (SV) was studied. In FLV-infected cells the amount of SV antigen formed was 2-3 times lower than in SV monoinfection, as indicated by immunofluorescence and cytofluorimetry. Electron microscopic examination showed that in mixed infection the number of newly formed SV particles decreased markedly (by 90%) despite the presence of compact aggregates of viral nucleocapsids in the cytoplasm. When the cells were initially infected with arbovirus and then superinfected with FLV, formation of virus antigen and virions of both viruses was not disturbed. Pre-treatment of cell monolayer with dactinomycin (0.2 mug/ml) blocked interferon production in MEC culture and inhibited interference between FLV and SV. It is assumed that interference between FLV and SV is associated with known mechanisms of interferon action as well as with disturbance of the stage of SV particles assembly and their release from the cell. Due to incomplete cycle of SV reproduction interrupted at the stage of ribonucleoprotein formation, productive type of its interaction with MEC cells is disturbed.