Semliki Forest virus multiplication in clones of Aedes albopictus cells

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Abstract
Clones of A. albopictus cells (115) were examined for their response to infection with semliki Forest virus. Virus yield and cytopathology showed a bimodal distribution. More than 68% of the clones gave low yields of virus (8 .times. 106-2 .times. 108 PFU[plaque-forming units]/ml) with no discernable cytopathology and 30% gave high yields of virus (1-8 .times. 109 PFU/ml) and showed moderate to severe cytopathology. To determine the level at which restriction in virus growth occurs in the low-virus-producing clones, the nature and extent of several virus-directed events in selected low-virus-producing clones were compared with the same events in high-virus-producing clones. Specifically, virus-specified polypeptide synthesis, positive- and negative-strand RNA synthesis, adsorption, uncoating and transfection with virion 42S RNA was compared. Whereas events before negative-strand RNA synthesis occurred to the same extent in all clones examined, negative-strand RNA synthesis and all subsequent virus-specified events were markedly reduced in the low-virus-producing lines, compared with the high-virus-producing lines. Thus, the restriction in virus growth in the low-virus-producing line occurs at the level of synthesis of negative-strand RNA. The consequence of this restriction in an early step in the virus multiplication cycle is discussed in terms of the survival of invertebrate cells after alphavirus infection.