User talk:H4moon/Phagocytosis

Cell death Cell death is an important process that plays a role in development, gets rid of defective cells, and fights cancer and pathogens. The three major forms of cell death are apoptotic, autophagic and necrotic. Phagocytosis usually follows cell death and phagoctyes eat and clean up the dead cells. Phagocytosis can also cause death of living cells. Phagocytic cell death is difficult to study because the process leaves no remains of the cell that could be studied.

Signaling in phagocytosis “Find me” signals are released which leads to chemotaxis of macrophages nearby. After reaching the target cell the macrophage’s recognition of the cell’s surface induces the “eat me” signal. The cell surface exposure of the phospholipid PS is one of the “eat me” signal. Several occurrences can lead to PS exposure. These processes include, calcium elevation, ATP depletion, oxidative stress, fusion of intracellular vesicles with plasma membrane, and necrosis. PS exposure can also happen on living cells. For example, various blood cells such as neutrophils, and lymphocytes activate the process of PS exposure upon encounter with pathogens or damage. The second major eat me signal is the cell surface calreticulin. Once on the surface of the cell, CRT induces phagocytosis. Cells also display don’t eat me signals including CD47, CD200, and CD31 to prevent being destroyed by phagocytosis. Therefore it is the net effect of the eat me and don’t eat me signals that determine whether a cell will be phagocytosed or not.

Clinical relevance Improper expression of the eat me and don’t eat me signals can result in various illnesses. Hemophagocytosis is a clinical condition where macrophages engulf viable blood cells causing reduced white or red cell count. Incorrect expression of the signals can also lead to cell cannibalism, neurodegeneration and cancer. Cancer cells over-express the don’t eat me signal CD47 causing formation of tumors by leaving damaged cells go unchecked.