Transcriptional and translational regulation of inflammatory mediator production by endogenous TGP-beta in macrophages that have ingested apoptotic cells

We recently reported that phagocytosis of apoptotic cells inhibits the rele ase of inflammatory cytokines by human macrophages, In this paper we show t hat apoptotic cell uptake by mouse J774 macrophages also inhibits the synth esis and secretion of the chemokines, macrophage inflammatory protein-2 (Mi p-2), KC, and Mip-1 alpha (but not that of monocyte chemoattractant protein -1 (MCP-1)/JE), and increases TGF-beta formation. Anti-TGF-beta neutralizin g Abs largely reversed the inhibitory effect of apoptotic cell uptake, and accordingly,exogenous TGF-beta down-regulated the synthesis of the same med iators. Apoptotic cell ingestion or TGF-beta also inhibited Mip-2 and Mip-1 alpha gene expression in LPS-treated J774 cells, whereas TNF-alpha mRNA le vels were unaffected. Importantly, TGF-beta pretreatment of J774 cells did not significantly alter chemokine and TNF mRNA stability, Finally, we found that apoptotic cell uptake and TGF-beta did not modulate NF-kappa B or AP- 1 DNA binding in J774 cells. We conclude that the decreased production of c hemokines and TNF resulting from apoptotic cell ingestion is largely mediat ed by a common event, i.e., feedback inhibition by endogenous TGF-beta, but involves different mechanisms. Whereas TNF-alpha production appears to be translationally down-regulated, the suppression of most chemokines investig ated appears to reflect transcriptional inhibition. In a broader context, t he impairment of chemokine and TNF generation by apoptotic cell uptake migh t represent an important mechanism contributing to the resolution of inflam mation, An additional consequence could be the selective recruitment of mon ocytes into inflammatory sites, as MCP-1/JE production by mouse macrophages was unaffected by apoptotic cell uptake, in contrast to other chemokines.