Editing Macrophage (section)

==== Phagocytosis of pathogens ====
[[File:Gram stain of a macrophage with ingested S epidermidis bacteria.jpg|thumb|[[Gram stain]] of a macrophage with ingested ''[[S. epidermidis]]'' bacteria, seen as purple granules within its [[cytoplasm]].]]
Macrophages can internalize antigens through receptor-mediated phagocytosis.<ref name="Fu-2021">{{cite journal | vauthors = Fu YL, Harrison RE | title = Microbial Phagocytic Receptors and Their Potential Involvement in Cytokine Induction in Macrophages | journal = Frontiers in Immunology | volume = 12 | pages = 662063 | date = 2021-04-29 | pmid = 33995386 | pmc = 8117099 | doi = 10.3389/fimmu.2021.662063 | doi-access = free }}</ref> Macrophages have a wide variety of [[pattern recognition receptor]]s (PRRs) that can recognize [[Pathogen-associated molecular pattern|microbe-associated molecular patterns]] (MAMPs) from pathogens. Many PRRs, such as [[toll-like receptor]]s (TLRs), [[Scavenger receptor (immunology)|scavenger receptors]] (SRs), C-type lectin receptors, among others, recognize pathogens for phagocytosis.<ref name="Fu-2021" /> Macrophages can also recognize pathogens for phagocytosis indirectly through [[opsonin]]s, which are molecules that attach to pathogens and mark them for phagocytosis.<ref name="Hirayama-2017">{{cite journal | vauthors = Hirayama D, Iida T, Nakase H | title = The Phagocytic Function of Macrophage-Enforcing Innate Immunity and Tissue Homeostasis | journal = International Journal of Molecular Sciences | volume = 19 | issue = 1 | pages = 92 | date = December 2017 | pmid = 29286292 | pmc = 5796042 | doi = 10.3390/ijms19010092 | doi-access = free }}</ref> Opsonins can cause a stronger adhesion between the macrophage and pathogen during phagocytosis, hence opsonins tend to enhance macrophages’ phagocytic activity.<ref>{{cite journal | vauthors = Uribe-Querol E, Rosales C | title = Phagocytosis: Our Current Understanding of a Universal Biological Process | journal = Frontiers in Immunology | volume = 11 | pages = 1066 | date = 2020-06-02 | pmid = 32582172 | pmc = 7280488 | doi = 10.3389/fimmu.2020.01066 | doi-access = free }}</ref> Both [[Complement system|complement proteins]] and antibodies can bind to antigens and opsonize them. Macrophages have complement receptor 1 (CR1) and 3 (CR3) that recognize pathogen-bound complement proteins C3b and iC3b, respectively, as well as fragment crystallizable γ receptors (FcγRs) that recognize the [[Fragment crystallizable region|fragment crystallizable (Fc) region]] of antigen-bound [[immunoglobulin G]] (IgG) antibodies.<ref name="Hirayama-2017" /><ref>{{cite journal | vauthors = Law SK | title = C3 receptors on macrophages | journal = Journal of Cell Science. Supplement | volume = 9 | issue = Supplement_9 | pages = 67–97 | date = 1988-01-01 | pmid = 2978518 | doi = 10.1242/jcs.1988.Supplement_9.4 | s2cid = 29387085 }}</ref> When phagocytosing and digesting pathogens, macrophages go through a [[respiratory burst]] where more oxygen is consumed to supply the energy required for producing reactive oxygen species (ROS) and other antimicrobial molecules that digest the consumed pathogens.<ref name="Punt-2018"/><ref>{{cite journal | vauthors = Forman HJ, Torres M | title = Reactive oxygen species and cell signaling: respiratory burst in macrophage signaling | journal = American Journal of Respiratory and Critical Care Medicine | volume = 166 | issue = 12 Pt 2 | pages = S4–S8 | date = December 2002 | pmid = 12471082 | doi = 10.1164/rccm.2206007 | s2cid = 22246117 }}</ref>