Apoptosis are induced in J774 macrophages upon phagocytosis and killing of Pseudomonas aeruginosa

Apoptosis induced by Pseudomonas aeruginosa in host cells plays a role in pathogenesis. However, little is known how the apoptosis of macrophages harboring P. aeruginosa affects the host or pathogen. In this study, the viability of J774 macrophages phagocytosing Pa IID1117 (elastase- and protease-positive) was significantly reduced (53.8 ± 4.5%) 48 h after infection and cell death occurred via apoptosis as seen by Hoechst 33258 staining and terminal deoxynucleotidyl transferase-mediated d-UTP nick end labeling (TUNEL) assay. An activated subunit of caspase 3 was found in the cellular lysate. Lower colony counts in infected cells and effective intracellular killing of bacteria were accompanied by enhanced apoptosis. Caspase 3 inhibiter inhibited apoptosis but did not prevent cell death and the extracellular leakage of bacteria. The apoptosis of the macrophages that phagocytose P. aeruginosa therefore inhibits the intracellular growth and spread of this bacterium and is important in host defense against P. aeruginosa infections.