Death mechanisms in cultured cells infected by Semliki Forest virus

We have investigated the induction of cell death in cultured cells by the virulent SFV4 and avirulent A7 strains of Semliki Forest virus (SFV). In BHK cells, death occurred by a typical apoptotic mechanism, as did the death of oligodendrocytes in glial cell cultures. For cerebellar neuron cultures, virus-induced death was due to necrosis. Although the SFV4 and A7 strains did not differ in the mechanism of induction of cell death, the virulent SFV4 strain did multiply to a higher titre in cultured neurons than the avirulent A7 strain. This is consistent with previous animal studies which indicate that the virulence of SFV strains is controlled by rapidity of multiplication in the CNS, leading to a lethal threshold of damage, rather than differential cell tropism or cell death mechanisms. The immune-mediated demyelination induced by avirulent strains may be triggered by apoptosis of oligodendrocytes, the consequences of which are obscured by death for virulent strains.