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 effe
ct on the progression of the infection to high acute phase titer, sugg
esting that intracellular factors alone are responsible for the restri
ction of virus production seen as the infection enters the persistent
phase. While persistently infected (over 1 year post infection) cell c
lones are morphologically indistinct from uninfected cells, they do di
splay a uniform 30% reduction in growth rate compared with uninfected
cells of the same clone. Using flow cytometry-based DNA content analys
is, 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 infe
cted cell cultures which are productively infected closely approximate
s the number of cells dying by apoptosis prompted us to investigate th
e role that cell death may play in the maintenance of the persistent i
nfection. Persistently infected cell cultures which were artificially
induced into apoptosis by short 45 degrees C heat treatments do not di
splay 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-te
rm maintenance of the persistent infection. (C) 1997 Elsevier Science
B.V.