Programmed cell death (apoptosis) in human monocytes infected by influenza A virus

Although infection of monocytes by influenza A virus primes for a high cytokine release, it also leads to cell death within 20-30 hours. In this brief report, we demonstrate that influenza A virus-induced monocyte killing was due to programmed cell death (apoptosis) and not to necrosis. Morphologically, chromatin condensation and margination occurred and biochemically, an apoptosis-specific internucleosomal DNA fragmentation into multimers of 180 bp ("DNA ladder") was found. Induction of apoptosis and not necrosis in influenza A virus-infected monocytes may serve three purposes: 1. Virus replication is limited, 2. a priming for a high cytokine response is initiated and 3. damaging and inflammation-inducing lysosomal enzymes are held back from monocytes undergoing controlled cell death.