Opsonin

Opsonins are extracellular proteins that, when bound to substances or cells, induce phagocytes to phagocytose the substances or cells with the opsonins bound.[1] Thus, opsonins act as tags to label things in the body that should be phagocytosed (i.e. eaten) by phagocytes (cells that specialise in phagocytosis, i.e. cellular eating).[1] Different types of things ("targets") can be tagged by opsonins for phagocytosis, including: pathogens (such as bacteria), cancer cells, aged cells, dead or dying cells (such as apoptotic cells), excess synapses, or protein aggregates (such as amyloid plaques). Opsonins help clear pathogens, as well as dead, dying and diseased cells.[2]

Opsonins were discovered and named "opsonins" in 1904 by Wright and Douglas, who found that incubating bacteria with blood plasma enabled phagocytes to phagocytose (and thereby destroy) the bacteria. They concluded that: “We have here conclusive proof that the blood fluids modify the bacteria in a manner which renders them a ready prey to the phagocytes. We may speak of this as an “opsonic” effect (opsono - I cater for; I prepare victuals for), and we may employ the term “opsonins” to designate the elements in the blood fluids which produce this effect.”[3]

Subsequent research found two main types of opsonin in blood that opsonised bacteria: complement proteins[4] and antibodies.[5] However, there are now known to be at least 50 proteins that act as opsonins for pathogens or other targets.[2]

  1. ^ a b Punt J, Stranford SA, Jones PP, Owen JA (2019). Kuby immunology (Eighth ed.). New York. ISBN 978-1-4641-8978-4. OCLC 1002672752.{{cite book}}: CS1 maint: location missing publisher (link)
  2. ^ a b Cockram, Tom O. J.; Dundee, Jacob M.; Popescu, Alma S.; Brown, Guy C. (2021). "The Phagocytic Code Regulating Phagocytosis of Mammalian Cells". Frontiers in Immunology. 12: 629979. doi:10.3389/fimmu.2021.629979. PMC 8220072. PMID 34177884.
  3. ^ Wright, A. E.; Douglas, S. R.; Sanderson, J. B. (September 1989). "An experimental investigation of the rôle of the blood fluids in connection with phagocytosis. 1903". Reviews of Infectious Diseases. 11 (5): 827–834. doi:10.1093/clinids/11.5.827. PMID 2682954.
  4. ^ Merle NS, Noe R, Halbwachs-Mecarelli L, Fremeaux-Bacchi V, Roumenina LT (2015). "Complement System Part II: Role in Immunity". Frontiers in Immunology. 6: 257. doi:10.3389/fimmu.2015.00257. PMC 4443744. PMID 26074922.
  5. ^ Chiu ML, Goulet DR, Teplyakov A, Gilliland GL (December 2019). "Antibody Structure and Function: The Basis for Engineering Therapeutics". Antibodies. 8 (4): 55. doi:10.3390/antib8040055. PMC 6963682. PMID 31816964.