Editing Macrophage (section)

=== Phagocytosis ===
{{Main|Phagocytosis}}
Macrophages are [[Phagocyte#Professional phagocytes|professional phagocytes]] and are highly specialized in removal of dying or dead cells and cellular debris. This role is important in chronic inflammation, as the early stages of inflammation are dominated by neutrophils, which expend themselves and are ingested by macrophages.<ref name="Macro17082013">{{cite journal | vauthors = Eming SA, Krieg T, Davidson JM | title = Inflammation in wound repair: molecular and cellular mechanisms | journal = The Journal of Investigative Dermatology | volume = 127 | issue = 3 | pages = 514–25 | date = March 2007 | pmid = 17299434 | doi = 10.1038/sj.jid.5700701 | quote = =Monocytes/macrophages. Unless stimuli for neutrophil recruitment persist at the wound site, the neutrophil infiltration ceases after few days, and expended neutrophils are themselves phagocytosed by macrophages, which are present at the wound side within 2 days after injury. | doi-access = free }}</ref> Macrophages normally present themselves at the wound site within 2 days following the injury.

The neutrophils are at first attracted to a site, where they perform their function and die, before they or their [[neutrophil extracellular traps]] are phagocytized by the macrophages.<ref name=Macro17082013/><ref>{{cite journal | vauthors = Monteith AJ, Miller JM, Maxwell CN, Chazin WJ, Skaar EP | title = Neutrophil extracellular traps enhance macrophage killing of bacterial pathogens | language = EN | journal = Science Advances | volume = 7 | issue = 37 | pages = eabj2101 | date = September 2021 | pmid = 34516771 | pmc = 8442908 | doi = 10.1126/sciadv.abj2101 | bibcode = 2021SciA....7.2101M | doi-access = free }}</ref> The first wave of neutrophils acts for approximately 2 days at the site and signals to attract macrophages. These macrophages will then ingest the aged neutrophils.<ref name="Macro17082013" />

The removal of dying cells is, to a greater extent, handled by ''fixed macrophages'', which will stay at strategic locations such as the lungs, liver, [[Nervous tissue|neural tissue]], bone, spleen and connective tissue, ingesting foreign materials such as pathogens and recruiting additional macrophages if needed.<ref>{{Cite journal| vauthors = Verma N, Saraf S |title=A Role of Macrophages: An Overview|date=2017-11-15|url=http://jddtonline.info/index.php/jddt/article/view/1521|journal=Journal of Drug Delivery and Therapeutics|language=en|volume=7|issue=6|pages=91–103|doi=10.22270/jddt.v7i6.1521|issn=2250-1177|doi-access=free}}</ref> The phagocytosis and clearance of apoptotic remains is called [[efferocytosis]] and is also carried out by other cell types, not all of which are professional phagocytes.

When a macrophage ingests a pathogen, the pathogen becomes trapped in a [[phagosome]], which then fuses with a [[lysosome]]. Within the [[phagolysosome]], [[enzymes]] and toxic peroxides digest the pathogen. However, some bacteria (such as ''[[Mycobacterium tuberculosis]])'' have become resistant to these methods of digestion. [[Typhoidal Salmonella|Typhoidal ''Salmonellae'']] induce their own phagocytosis by host macrophages in vivo and inhibit digestion by lysosomal action, thereby using macrophages for their own replication and causing macrophage apoptosis.<ref>{{cite journal| vauthors = YashRoy RC |date=2000|title=Hijacking of Macrophages by Salmonella (310r) Through 'Types III' Secretion Like Exocytotic Signalling : A Mechanism for Infection of Chicken Ileum|url=https://www.researchgate.net/publication/230823526|journal=Indian Journal of Poultry Science|volume=35|issue=3|pages=276–281}}</ref> Macrophages are capable of engulfing and digesting many bacteria during their life. They can die eventually due to factors including pathogenic cytotoxicity, oxidative stress, and phagocytosis-induced apoptosis.<ref>{{Cite journal |last=Kirschnek |first=Susanne |last2=Ying |first2=Songmin |last3=Fischer |first3=Silke F. |last4=Häcker |first4=Hans |last5=Villunger |first5=Andreas |last6=Hochrein |first6=Hubertus |last7=Häcker |first7=Georg |date=2005-01-15 |title=Phagocytosis-Induced Apoptosis in Macrophages Is Mediated by Up-Regulation and Activation of the Bcl-2 Homology Domain 3-Only Protein Bim1 |url=https://journals.aai.org/jimmunol/article/174/2/671/72667/Phagocytosis-Induced-Apoptosis-in-Macrophages-Is? |journal=The Journal of Immunology |volume=174 |issue=2 |pages=671–679 |doi=10.4049/jimmunol.174.2.671 |issn=0022-1767}}</ref> Phagocytosis-induced apoptosis results from the powerful apoptotic stimulus of consuming bacteria and is observed in (at least) macrophages and neutrophils.