Apoptosis, but not necrosis, of infected monocytes is coupled with killing of intracellular bacillus Calmette-Guérin.

TLDR

The study investigates how killing infected monocytes affects the survival of intracellular BCG. Monocytes were infected with a single BCG, cultured for 6–8 days, then treated with H₂O₂ or ATP to induce necrosis or apoptosis, respectively. H₂O₂‑induced necrosis did not affect BCG viability, whereas ATP‑induced apoptosis caused DNA fragmentation, vacuole swelling, and a marked decrease in intracellular BCG survival.

Abstract

We have examined the effect of killing of host monocytes infected with bacillus Calmette-Guérin (BCG) on the viability of the intracellular mycobacteria. Peripheral blood monocytes were infected in vitro with a single bacillus per cell and maintained in culture for 6-8 d to allow the bacilli to replicate. Replicating viable BCG were found singly in perinuclear vacuoles bounded by tightly apposed lipid bilayers. Monocytes were then exposed to toxic mediators that induced killing of cells as evaluated by 51Cr release into the culture medium. Both hydrogen peroxide (H2O2) (an inducer of cell necrosis) and adenosine triphosphate (ATP4-) (an inducer of cell apoptosis) treatment killed infected monocytes. H2O2-induced killing had no effect on BCG viability. ATP-induced cell death was accompanied by DNA fragmentation and nuclear condensation. Apoptosis was associated with a swelling of the phagocytic vacuoles which became multibacillary and with a reduction of BCG viability as enumerated by colony-forming units.