Changes in Bcl-2 expression in vaccinia virus-infected human peripheral blood monocytes

In this study, we show that Bcl-2, one of the most important antiapoptotic agents, is expressed in a phase-dependent manner in the human adherent monocytes after vaccinia virus infection, reflecting the viral infection stages. Early viral infection induced Bcl-2 expression in a level higher than in control cells. At 14 h post-infection (p.i.), the Bcl-2 level measured in the whole cell extracts dramatically decreased, followed by the increase at 24 h p.i. The levels of active dephosphorylated Bcl- 2 protein present in the cells reflected the gene expression character, but were much lower than in case of a heat shock. The dramatic increase of Bcl-2 protein level in the nuclear fraction at 4 h p.i. was observed. Changes in Bcl-2 mRNA content in elutriated human blood monocytes isolated from the same donor showed different kinetics, increasing up to 12 h p.i. and diminishing to undetectable level at 24 h p.i. concomitantly with a severe increase in the number of dead cells. The results indicate that virally infected adherent monocytes remain resistant to apoptosis, while freshly isolated monocytes undergo apoptotic cell death. These results throw new light on the apoptotic mechanism in the monocyte-derived cells after vaccinia virus infection in vitro.