Requirements for apoptotic cell contact in regulation of macrophage responses

M Lucas, LM Stuart, A Zhang… - The Journal of …, 2006 - journals.aai.org
M Lucas, LM Stuart, A Zhang, K Hodivala-Dilke, M Febbraio, R Silverstein, J Savill…
The Journal of Immunology, 2006journals.aai.org
An important consequence of macrophage engulfment of apoptotic cells is suppression of
inflammatory responses, which was first defined by assay of TNF-α release stimulated by
LPS. These effects are apparently mediated in part by paracrine effects of TGF-β released by
the subset of stimulated macrophages that ingest apoptotic cells, which suppresses
neighboring cells. However, the apoptotic cell-derived signal that stimulates TGF-β release,
and the nature of any additional signals required for the anti-inflammatory response remain …
Abstract
An important consequence of macrophage engulfment of apoptotic cells is suppression of inflammatory responses, which was first defined by assay of TNF-α release stimulated by LPS. These effects are apparently mediated in part by paracrine effects of TGF-β released by the subset of stimulated macrophages that ingest apoptotic cells, which suppresses neighboring cells. However, the apoptotic cell-derived signal that stimulates TGF-β release, and the nature of any additional signals required for the anti-inflammatory response remain poorly defined. In this study, we investigate the requirements for apoptotic cell engagement of macrophage surface receptors in these responses. We show that the apoptotic cell receptors CD36 and α v β 3 contribute to apoptotic cell phagocytosis by mouse macrophages, but are not essential for anti-inflammatory responses, suggesting that the mechanisms of response and phagocytosis are separate. In further defining requirements for response, we confirm the importance of TGF-β in suppression by apoptotic cells, and identify an additional level of control of these effects. We show that LPS-stimulated mouse macrophage TNF-α release is only suppressed if macrophages have first contacted apoptotic cells, and hence, bystander macrophages are refractory to TGF-β released by phagocytosing macrophages. We conclude that the profound suppression of LPS-driven TNF-α release by macrophage populations requires hitherto obscure contact-dependent licensing of macrophage responsiveness to TGF-β by apoptotic cells.
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