APOPTOSIS, BUT NOT NECROSIS, OF INFECTED MONOCYTES IS COUPLED WITH KILLING OF INTRACELLULAR BACILLUS-CALMETTE-GUERIN

We have examined the effect of killing of host monocytes infected with bacillus Calmette-Guerin (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. Monoc ytes were then exposed to toxic mediators that induced killing of cell s as evaluated by Cr-51 release into the culture medium. Both hydrogen peroxide (H2O2) (an inducer of cell necrosis) and adenosine triphosph ate (ATP(4-)) (an inducer of cell apoptosis) treatment killed infected monocytes. H2O2-induced killing had no effect on BCG viability. ATP-i nduced cell death was accompanied by DNA fragmentation and nuclear con densation. Apoptosis was associated with a swelling of the phagocytic vacuoles which became multibacillary and with a reduction of BCG viabi lity as enumerated by colony-forming units.