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37.6: Phagocytosis of Apoptotic Cells

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Cell Biology

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Phagocytosis of Apoptotic Cells

37.6: Phagocytosis of Apoptotic Cells

Cells undergoing apoptosis form apoptotic bodies that must be removed immediately to prevent inflammation, autoimmune diseases, and necrosis. Phagocytosis is carried out by professional phagocytes such as macrophages or  immature dendritic cells. Non-professional phagocytes such as  epithelial cells and fibroblasts also take part in this process; however, they are not as effective as professional phagocytes. 

Normal cells contain receptors that prevent them from being recognized by phagocytes. For example, red blood cells display CD47 receptors that block phagocytosis. Another marker, CD31, also known as platelet endothelial cell adhesion molecule-1, is expressed by normal cells, which prevents phagocyte attachment. During apoptosis, CD31 is not expressed, leading to phagocyte recognition and phagocytosis.

Apoptotic cells release 'find-me' signals such as  lysophosphatidylcholine, sphingosine-1-phosphate, fractalkine, thrombospondin-1, ATP, and UTP to help phagocyte recognition. Once the phagocytes reach the location, the apoptotic cells display 'eat-me' signals, such as apoptotic cell-associated molecular patterns (ACAMP) and phosphatidylserine. When phagocytes attach to apoptotic cells, they release anti-inflammatory cytokines such as IL-10 and TGF-ꞵ, creating a non-inflammatory microenvironment. This prevents damage to neighboring cells. Once the apoptotic cells are internalized, they are broken down into nucleotides, amino acids, and sterols which are further recycled.


Phagocytosis Apoptotic Cells Inflammation Autoimmune Diseases Necrosis Professional Phagocytes Macrophages Immature Dendritic Cells Non-professional Phagocytes Epithelial Cells Fibroblasts Receptors CD47 Receptors CD31 Marker Find-me Signals Lysophosphatidylcholine Sphingosine-1-phosphate Fractalkine Thrombospondin-1 ATP UTP Eat-me Signals Apoptotic Cell-associated Molecular Patterns (ACAMP) Phosphatidylserine Anti-inflammatory Cytokines IL-10 TGF-β

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