Phagocytosis: Difference between revisions

[[File:Process of Phagocytosis.svg|thumb|The engulfing of a pathogen by a phagocyte]]

In a [[Multicellular organism|multicellular organism's]] [[immune system]], phagocytosis is a major mechanism used to remove [[pathogen]]s and cell debris. The ingested material is then digested in the phagosome. Bacteria, dead tissue cells, and small mineral particles are all examples of objects that may be phagocytized. Some [[protozoa]] use phagocytosis as means to obtain nutrients.

 

==History==

Following [[apoptosis]], the dying cells need to be taken up into the surrounding tissues by macrophages in a process called [[efferocytosis]]. One of the features of an apoptotic cell is the presentation of a variety of intracellular molecules on the cell surface, such as [[calreticulin]], [[phosphatidylserine]] (from the inner layer of the plasma membrane), [[annexin A1]], oxidised [[LDL]] and altered [[glycans]].<ref name="pmid22074924">{{cite journal | vauthors = Bilyy RO, Shkandina T, Tomin A, Muñoz LE, Franz S, Antonyuk V, Kit YY, Zirngibl M, Fürnrohr BG, Janko C, Lauber K, Schiller M, Schett G, Stoika RS, Herrmann M | title = Macrophages discriminate glycosylation patterns of apoptotic cell-derived microparticles | journal = The Journal of Biological Chemistry | volume = 287 | issue = 1 | pages = 496–503 | date = January 2012 | pmid = 22074924 | pmc = 3249103 | doi = 10.1074/jbc.M111.273144 | doi-access = free }}</ref> These molecules are recognised by receptors on the cell surface of the macrophage such as the phosphatidylserine receptor or by soluble (free-floating) receptors such as [[thrombospondin 1]], [[GAS6]], and [[MFGE8]], which themselves then bind to other receptors on the macrophage such as [[CD36]] and [[alpha-v beta-3|alpha-v beta-3 integrin]]. Defects in apoptotic cell clearance is usually associated with impaired phagocytosis of macrophages. Accumulation of apoptotic cell remnants often causes autoimmune disorders; thus pharmacological potentiation of phagocytosis has a medical potential in treatment of certain forms of autoimmune disorders.<ref name="pmid19838202">{{cite journal | vauthors = Mukundan L, Odegaard JI, Morel CR, Heredia JE, Mwangi JW, Ricardo-Gonzalez RR, Goh YP, Eagle AR, Dunn SE, Awakuni JU, Nguyen KD, Steinman L, Michie SA, Chawla A | title = PPAR-delta senses and orchestrates clearance of apoptotic cells to promote tolerance | journal = Nature Medicine | volume = 15 | issue = 11 | pages = 1266–72 | date = November 2009 | pmid = 19838202 | pmc = 2783696 | doi = 10.1038/nm.2048 }}</ref><ref>{{cite journal|last=Roszer|first=T|author2=Menéndez-Gutiérrez, MP |author3=Lefterova, MI |author4=Alameda, D |author5=Núñez, V |author6=Lazar, MA |author7=Fischer, T |author8= Ricote, M |title=Autoimmune kidney disease and impaired engulfment of apoptotic cells in mice with macrophage peroxisome proliferator-activated receptor gamma or retinoid X receptor alpha deficiency|journal=Journal of Immunology|date=Jan 1, 2011|volume=186|issue=1|pages=621–31|pmid=21135166|doi=10.4049/jimmunol.1002230|pmc=4038038}}</ref><ref>{{cite journal|last=Kruse|first=K|author2=Janko, C |author3=Urbonaviciute, V |author4=Mierke, CT |author5=Winkler, TH |author6=Voll, RE |author7=Schett, G |author8=Muñoz, LE |author9= Herrmann, M |title=Inefficient clearance of dying cells in patients with SLE: anti-dsDNA autoantibodies, MFG-E8, HMGB-1 and other players|journal=Apoptosis|date=September 2010|volume=15|issue=9|pages=1098–113|pmid=20198437|doi=10.1007/s10495-010-0478-8|s2cid=12729066}}</ref><ref>{{cite journal|last=Han|first=CZ|author2=Ravichandran, KS|title=Metabolic connections during apoptotic cell engulfment|journal=Cell|date=Dec 23, 2011|volume=147|issue=7|pages=1442–5|pmid=22196723|doi=10.1016/j.cell.2011.12.006|pmc=3254670}}</ref>[[Image:Trophozoites of Entamoeba histolytica with ingested erythrocytes.JPG|thumb|Trophozoites of ''Entamoeba histolytica'' with ingested erythrocytes]]

==In protists==

 

* In some, such as [[amoeba]], phagocytosis takes place by surrounding the target object with [[pseudopod]]s, as in animal phagocytes. In humans, the amoebozoan ''[[Entamoeba histolytica]]'' can phagocytose [[red blood cell]]s.

* [[Ciliate]]s also engage in phagocytosis.<ref name="pmid12089212">{{cite journal | vauthors = Grønlien HK, Berg T, Løvlie AM | title = In the polymorphic ciliate Tetrahymena vorax, the non-selective phagocytosis seen in microstomes changes to a highly selective process in macrostomes | journal = The Journal of Experimental Biology | volume = 205 | issue = Pt 14 | pages = 2089–97 | date = July 2002 | doi = 10.1242/jeb.205.14.2089 | pmid = 12089212 }}</ref> In ciliates there is a specialized groove or chamber in the cell where phagocytosis takes place, called the [[cytostome]] or mouth.

 

 

[[Mixotrophy]] can involve phagotrophic nutrition and [[phototroph]]ic nutrition.<ref name="pmid12812372">{{cite journal | vauthors = Stibor H, Sommer U | title = Mixotrophy of a photosynthetic flagellate viewed from an optimal foraging perspective | journal = Protist | volume = 154 | issue = 1 | pages = 91–8 | date = April 2003 | pmid = 12812372 | doi = 10.1078/143446103764928512 }}</ref>