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. Author manuscript; available in PMC: 2017 May 1.
Published in final edited form as: Stem Cells. 2016 Feb 29;34(5):1142–1150. doi: 10.1002/stem.2326

Figure 1. Silent clearance of apoptotic cells.

Figure 1

In the steady-state, cells undergoing apoptosis release soluble factors, which include immuno-regulatory mediators, “keep out” signals (that prevent migration of neutrophils), and “find me” signals (that attract professional phagocytes). Apoptotic cells expose PtdSer and other ACAMPs. Externalized PtdSer binds PtdSer receptors directly or through bridge molecules. ACAMPs are recognized directly by PRRs expressed on the phagocyte membrane. Internalization of apoptotic cells exerts immuno-regulatory effects on target APCs, by down-regulating expression of Ag-presenting (MHC class-I and –II) and T cell co-stimulatory molecules (CD80, CD86), augmenting IDO, reducing secretion of pro-inflammatory cytokines (IL-1β, TNF-α, IL-6, IL-12p70, IL-23), and increasing release of immunosuppressive mediators (IL-10, TGF-β). ACAMPs, Apoptotic-Cell-Associated Molecular Patterns; DC, dendritic cell; MØ, macrophage; PRRs, pattern recognition receptors; PtdSer, phosphatidylserine.