Phagocytes and apoptotic cell interplay

Apoptotic cells are usually cleared by phagocytosis in vivo with a rapid and efficient process aimed to remove damaged cells and components and to inhibit inflammation. Apoptosis induces cell surface changes that are important for recognition and engulfment of cells by phagocytes. These changes include recognition and tethering molecules on the surface of apoptotic cells, like alteration in surface sugars, externalisation of phosphatidylserine, oxidized phospholipids and qualitative changes in the adhesion molecules ICAM-3. In non-pathological conditions, an efficient clearance is assured by the redundant interaction between apoptotic cell ligands and multiple molecules present on the engulfing cell surface. The apoptotic cell engulfment appears to activate signals able to suppress release of pro-inflammatory cytokines, thus pro-inflammatory responses are not elicited. In this chapter we will review the recognition and signalling mechanisms involved in the phagocytosis of apoptotic cells and the consequences of impaired phagocytosis on development of diseases as well as consequences on inflammation and immune responses.