Characterization of the infection of Aedes albopictus cell clones by Sindbis virus. 

Karpf AR, Blake JM, Brown DT 

Cell Research Institute, University of Texas at Austin, USA.

We have investigated the infection of Aedes albopictus (mosquito) cell clones by Sindbis virus. Variation in the multiplicity of infection
(MOI) from ranges of 50-0.00005 pfu/cell was determined to have no effect on the progression of the infection to high acute phase
titer, suggesting that intracellular factors alone are responsible for the restriction of virus production seen as the infection enters the
persistent phase: While persistently infected (over 1 year post infection) cell clones are morphologically indistinct from uninfected cells,
they do display a uniform 30% reduction in growth rate compared with uninfected cells of the same clone. Using flow cytometry-based
DNA content analysis, we found that persistent Sindbis virus infection induces distinct cytological effects on these cells, including an
increase in apoptosis and polyploidy in one clone and cell cycle phase effects in another. Finally, the observation that the number of
cells in persistently infected cell cultures which are productively infected closely approximates the number of cells dying by apoptosis
prompted us to investigate the role that cell death may play in the maintenance of the persistent infection. Persistently infected cell
cultures which were artificially induced into apoptosis by short 45 degrees C heat treatments do not display increased Sindbis virus
production. This result does not support the hypothesis that infection sensitivity induced by random apoptosis in persistently infected
cell cultures is responsible for the long-term maintenance of the persistent infection.