INTERACTION OF YERSINIA-ENTEROCOLITICA WITH MACROPHAGES LEADS TO MACROPHAGE CELL-DEATH THROUGH APOPTOSIS

Suppression of the host defense is one of the hallmarks of Yersinia en terocolitica infection. This enteric pathogen resists phagocytosis and interferes with macrophage functions from an extracellular localizati on (oxidative-burst generation and tumor necrosis factor alpha product ion). In this study, we investigated the fate of the Y. enterocolitica -infected macrophage. We found that murine J774A.1 macrophages and mac rophages derived from human monocytes were killed by infection with Y. enterocolitica. Analysis of cellular morphology and DNA fragmentation revealed that macrophage cell death occurs through the induction of a poptosis. A total of 92% +/- 5% (mean +/- standard deviation) of murin e J774A.1 macrophages and 74% +/- 6% of human monocyte-derived macroph ages underwent apoptosis upon Yersinia infection after 4 and 20 h, res pectively The broad-spectrum caspase inhibitor Z-Val-Ala-DL-Asp-fluoro methylketone blocked completion of the Yersinia-induced apoptotic prog ram but not the surface exposure of phosphatidylserine as an early-sta ge apoptotic event. Analysis of different Yersinia mutants showed that macrophage apoptosis depends on a functional Y. enterocolitica type I II protein secretion system. Apoptotic cell death of macrophages was n ot related to the YopE-mediated cytotoxic effect of Yersinia, since di sruption of actin microfilaments by a Y. enterocolitica strain express ing a restricted repertoire of yop genes, including YopE, did not resu lt in macrophage apoptosis. Furthermore, Yersinia-induced cytotoxic al terations in epithelial HeLa cells, which are conferred by YopE, did n ot lead to apoptosis. Our data demonstrate for the first time that Y. enterocolitica promotes the apoptosis of macrophages, an effect which is clearly distinct from the morphological alterations mediated by Yer sinia on epithelial HeLa cells.