Figure 2.

The induction of efferocytosis requires two signals: presentation of “eat-me” signals and loss of “don’t-eat-me” signals. Apoptotic cells are recognized by a variety of receptors through various ligands presented on their cell surface. PtdSer is the most common ligand and is bound both directly by receptors and indirectly via opsonins such as MFG-E8. Other apoptotic cell ligands include calreticulin, which normally resides within the endoplasmic reticulum. Opposing efferocytosis are the “don’t-eat-me” signals such as CD47, which, via SIRPα on the efferocyte, inhibit the signaling of efferocytic receptors.