Execution and elimination of apoptotic cells

Abstract

The uptake of apoptotic cells by professional phagocytes like macrophages is not only a non-inflammatory but also an active anti-inflammatory process.a)To examine these immunomodulating effects of dying cells an in vitro co-culture system using primary murine cells was established.b)Co-incubation of macrophages with apoptotic cells followed by stimulation with LPS resulted in a decrease of inflammatory TNFá and an increase of anti-inflammtory IL­10 release and thereby changed the response of macrophages, when compared with LPS stimulation alone. Similar results were obtained with as different target cells as apoptotic isogenic mouse thymoma S49.1 cells, Jurkat T cells or primary thymocytes. Interestingly, some types of necrotic cells such as ATP-depleted Jurkat T cells had also anti-inflammatory effects in the co-culture system.c)The effect apoptotic cells have on other macrophage functions, i.e. phagocytosis, was examined with a sensitive assay, based on fluorescence labelled E.coli particles. Pre-incubation with apoptotic cells had no effect on E.coli phagocytosis.In cases of massive apoptosis the phagocytic capacity can be limited and secondary lysis occurs. Caspase-3 release should be detected under these circumstances.a)Stable activity of recombinant caspase-3 was demonstrated in several biological fluids by DEVD-afc cleavage.b)Caspase-3 activity could be detected in vitro in the supernatant of apoptotic cells.Hsp70 can be released from necrotic cells and is also expressed on the surface of stressed cell as a danger-signal . Hsp70 was postulated to take the function of an inflammatory cytokine.a)Addition of some Hsp70 preparations was found to induce macrophages to produce inflammatory mediators.b)The use of two low endotoxin Hsp70 preparations reproducibly failed to induce this response.