Opsonization- Definition, Mechanism, Opsonins, Examples (2023)

Opsonization definition

  • The term opsonization refers to the capacity of antibodies and complement components (as well as other proteins) to coat dangerous antigens that can then be recognized by antibodies or complement receptors on phagocytic cells.
  • Opsonization is the molecular mechanism whereby molecules, microbes, or apoptotic cells are chemically modified to have stronger interactions with cell surface receptors on phagocytes and antibodies.
  • This is the mechanism of identifying invading particles (antigens) by the use of specific components called opsonins.
  • The opsonins act as markers or tags that allow recognition by the immune system of the body.
  • An opsonin is any molecule that enhances phagocytosis bymarking anantigenfor an immune response or marking dead cells for recycling.
  • The purpose of opsonization is to make the antigens palatable to the antibody or the phagocytic cells.

Mechanism of Opsonization

  • Opsonization of pathogens can occur via antibodies or the complement system.

Antibody-mediated Opsonization

Opsonization- Definition, Mechanism, Opsonins, Examples (1)

Figure: 1) Antibodies (A) and pathogens (B) free roam in the blood. 2) The antibodies bind to pathogens and can do so in different formations such as opsonization (2a), neutralization (2b), and agglutination (2c). 3) A phagocyte (C) approaches the pathogen, and the Fc region (D) of the antibody binds to one of the Fc receptors (E) on the phagocyte. 4) Phagocytosis occurs as the pathogen is ingested. Source: Wikipedia.

  • The mechanism of opsonization is employed by antibodies in order to inhibit and clear infection.
  • Antibody-mediated opsonization by antibodies involves the coating of pathogens with antibodies so that they are recognized and phagocytosed by innate immune cells.
  • Encapsulated bacteria that resist phagocytosis become extremely attractive to neutrophils and macrophages when coated with antibody and their rate of clearance from the bloodstream is strikingly enhanced.
  • As the structure of immunoglobulins was deciphered, it was apparent that IgG is the heat-stable serum factor responsible for antigen-specific opsonization.
  • IgG combines by its two antigen-binding pieces, Fab, with antigenic determinants on the surface of the microorganism (or another particle).
  • Upon combination with antigen, the IgG molecule undergoes specific conformational and configurational changes in the F(ab)2 hinge region.
  • Phagocytic cells of all types have receptors for the IgG molecule on their plasma membranes.
  • The number of these receptors on each mouse peritoneal and alveolar has been estimated at 1-2 million. These receptors are resistant to tryptic proteolysis and mediate binding of IgG-coated particles at 4°C as well as at 37°C and in the absence of divalent cations.
  • Even though all four subclasses of human IgG bind to the antigen, only IgG1, and IgG3 are capable of binding to receptors on phagocytic cells.
  • The phagocytic cell’s receptors for IgG bind only to the Fc portion of the molecule, and are therefore known as Fc receptors.
  • In the case of antibody-mediated opsonization, binding of a pathogen (antigen)-antibody complexes to an Fc receptor on phagocytes will induce internalization of the complex and internal digestion of the pathogen in lysosomes.
  • Generally, multiple antibodies bind to various sites on the antigen, increasing the chance andefficiencyin which the pathogenis engulfedin the phagosome and destroyed by lysosomes.

Complement-mediated Opsonization

  • The complement system is composed of over 30 proteins that improve the ability of antibodies and phagocytic cells to fight invading organisms.
  • It initiates phagocytosis by opsonizing antigens. This system is also responsible for enhancing inflammation and cytolysis.
  • The most critical heat-labile opsonin, and perhaps the most essential opsonin of all, is C3b (C3b is the fragment of C3 that binds to particles when C3 is cleaved by a C3-convertase).
  • Either through the classical pathway (initiated with binding of IgG or IgM molecules to antigen, which results in binding and activation of the C 1 complex) or the alternate pathway (initiated by the presence of lipid-carbohydrate complexes found in the cell wall of bacteria), C3 is cleaved into C3a and C3b.
  • It is C3b that binds to the surface of the particle and serves as an opsonin.
  • Once a particle is coated with C3b, it must then be recognized by and bound to, the surface of a phagocytic cell before it can be ingested.
  • The mechanisms by which these events occur have been partially characterized. All mononuclear phagocytes and polymorphonuclear leukocytes thus far studied have receptors on their plasma membranes for C3b.
  • However, the binding of C3b-coated particles to C3b receptors of some cells requires the presence of divalent cations in the medium.
  • The activated macrophages then ingest particles coated with C3b.
  • Besides, in microorganisms like Hemophilus influenza, C3b cleaves the aromatic dipeptides present in the neutrophils as C3b has an enzymatic activity for aromatic dipeptides.
  • The cleavage of aromatic dipeptides on the neutrophil’s plasma membrane is considered as a means by which C3b mediates phagocytosis of particles to which it is bound.

Opsonins and Types

Opsonization- Definition, Mechanism, Opsonins, Examples (2)

(Video) Opsonization (FL-Immuno/11)

Figure: Action of opsonins: A phagocytic cell recognizes the opsonin on the surface of an antigen. Source: Wikipedia.

  • An opsonin is any molecule that enhances phagocytosis bymarking anantigenfor an immune response or marking dead cells for recycling.
  • Opsonin molecules usually bind, on one end, to the receptors present in the antigen and, on the other end, to the receptors on the phagocytes.
  • This binding results in different mechanisms that ultimately lead to the destruction or removal of the particular antigen.
  • Opsonin molecules ensure that the binding of the antigen to the immune cells is greatly enhanced.
  • Opsonins have important roles in the immune system like marking of dead and dying cells for clearance by macrophages and neutrophils.
  • Besides, opsonins also aid in activating the complement proteins and destruction of cells by natural killer (NK) cells.
  • The mechanisms utilized by opsonins to enhance the kinetics of phagocytosis involve favoring the interaction between opsonin and cell surface receptors on the immune cells.
  • These molecules override the negative charges on the cell membrane, which make it difficult for two cells to come close together.

Types

  • Opsonins involved in the immune system include the following molecules:

Antibodies

  • Antibodies are the molecules of the adaptive immunity that are released by B cells as an immune response.
  • In the case of IgG antibodies, the presence of the Fc domain allows the binding of receptors on the phagocytes to the Fc domain while the Fab domain of the antibody binds to the antigen.
  • IgM antibodies, however, lack the Fc receptors and thus, are ineffective in enhancing phagocytosis. But they are highly effective in activating the complement system and are considered as an opsonin.
  • The binding of antibodies to the antigen and the immune cells results in the release of lysis products from the effector cells.

Complement proteins

  • Among the various complement proteins, C3b, C4b, and C1q are the common proteins that also serve as opsonins.
  • C3b is by far the most effective opsonin that initiates phagocytosis as it can be recognized by phagocyte receptors.
  • One added advantage with complement proteins acting as opsonin is that Complement receptor 1 is expressed in all phagocytes and recognizes several complement proteins like C3b and C4b.
  • C1q is a part of the C1 complex which interacts with the Fc region of antibodies and performs as an opsonin.

Circulating proteins

  • A number of circulating proteins like pentraxins,collectins, andficolins also serve as opsonins.
  • These proteins are the PRRs (pattern recognizing receptors) capable of coating the microbes as an opsonin, which enhances the activity of neutrophils by several mechanisms.
  • A significant property of these proteins is the ability to bind in a Ca‐dependent fashion, as a pattern recognition molecule, to several microorganisms that contain phosphorylcholine in their membranes which then activates the complement system.
  • Collectins like Mannose Binding Lectin (MBL) is the basis for the lectin pathway of complement activation.
  • Ficolins, in turn, typically recognize N‐acetylglucosamine residues in complex‐type carbohydrates in addition to other ligands on different antigens.

Examples

The common opsonins are:

  • IgM antibodies
  • IgG antibodies
  • C3b proteins
  • C4b proteins
  • C1q proteins
  • Pentraxins
  • Collectins
  • Ficolins
  • Mannose-binding lectin (MBL)

References

  • Peter J. Delves, Seamus J. Martin, Dennis R. Burton, and Ivan M. Roitt(2017). Roitt’s Essential Immunology, Thirteenth Edition. John Wiley & Sons, Ltd.
  • Judith A. Owen, Jenni Punt, Sharon A. Stranford (2013). Kuby Immunology. Seventh Edition. H. Freeman and Company
  • Thau L, Mahajan K. Physiology, Opsonization. [Updated 2020 Mar 25]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2020 Jan-.Available from: https://www.ncbi.nlm.nih.gov/books/NBK534215/
  • Griffin F.M. (1977) Opsonization. In: Day N.K., Good R.A. (eds) Biological Amplification Systems in Immunology. Comprehensive Immunology, vol 2. Springer, Boston, MA

Sources

  • 4% – https://www.ncbi.nlm.nih.gov/books/NBK534215/
  • 2% – https://patents.google.com/patent/US20040013673A1/en
  • 2% – https://makkypedia.blogspot.com/2016/06/opsonization.html
  • 1% – https://www.sciencedirect.com/topics/immunology-and-microbiology/immunoglobulin-g
  • 1% – https://www.sciencedirect.com/book/9780120442201/methods-for-studying-mononuclear-phagocytes
  • 1% – https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4139653/
  • 1% – https://quizlet.com/93116857/immunology-chapters-2-and-3-flash-cards/
  • 1% – https://quizlet.com/74073384/ap-ii-chpt-21-the-immune-system-flash-cards/
  • <1% – https://www.sciencedirect.com/topics/immunology-and-microbiology/opsonization
  • <1% – https://www.sciencedirect.com/science/article/pii/S0006349500766021
  • <1% – https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4559511/
  • <1% – https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4019044/
  • <1% – https://www.ncbi.nlm.nih.gov/pmc/articles/PMC344229/
  • <1% – https://quizlet.com/187777219/lectin-pathway-classical-and-rest-of-chapter-3-flash-cards/
  • <1% – https://deepblue.lib.umich.edu/bitstream/handle/2027.42/25474/0000014.pdf?sequence=1
(Video) What is Opsonization? | Immunology Made Easy for Students | V-Learning™

FAQs

What is example of opsonization? ›

Examples of opsonins are antibody molecules such as the IgM that are capable of activating the complement system to increase the susceptibility of antigens to phagocytosis. Apart from phagocytosis, opsonization can also promote antibody-dependent cell-mediated cytotoxicity.

What is the mechanism of opsonization? ›

Opsonization is an immune process which uses opsonins to tag foreign pathogens for elimination by phagocytes. Without an opsonin, such as an antibody, the negatively-charged cell walls of the pathogen and phagocyte repel each other.

What are some examples of opsonins? ›

Examples of opsonins include IgG antibody - part of the immune response - and the C3b molecule of the complement system. Each has receptors for both foreign particle and host phagocyte.

What are opsonins made of? ›

They comprise the adaptive opsonization pathway, and are composed of two fragments: the antigen binding region (Fab region) and the fragment crystallizable region (Fc region). The Fab region is able to bind to a specific epitope on an antigen, such as a specific region of a bacterial surface protein.

What is the definition of opsonin? ›

Definition of opsonin

: any of various proteins (such as antibodies or complement) that bind to foreign particles and cells (such as bacteria) making them more susceptible to the action of phagocytes.

What is opsonins function? ›

The function of opsonins is to react with bacteria and make them more susceptible to ingestion by phagocytes. Opsonization of bacteria may occur by three different mechanisms. First, specific antibody alone may act as an opsonin.

Why is opsonization important? ›

Opsonization is the important process in host defense by which particles or complexes are made readily ingestible for uptake by phagocytic cells. Specific serum proteins, known as opsonins, coat particles and cause the particles to bind avidly to phagocytes and trigger ingestion.

Which antibodies are opsonins? ›

IgG anti–red cell autoantibodies are opsonins; when bound to autoantigens on red cell membranes, they instigate phagocytosis of the cells by macrophages.

Which of the following is opsonin? ›

The answer is a. C3b. C3b is the central molecule of the complement cascade which is produced in all 3 pathways. It opsonizes bacteria and it may also combine with other complement components to produce C5 convertase.

Is opsonin a protein? ›

An opsonin generally is a protein substance, such as one of the circulating immunoglobulins or complement components.

What molecules are opsonins? ›

An opsonin is any molecule that acts as a binding enhancer for the process of phagocytosis, for example, by coating the negatively-charged molecules on the membrane.
...
Examples
  • antibodies: IgG and IgA.
  • components of the complement system: C3b, C4b, and iC3b.
  • Surfactant.
  • Mannose-binding lectin (initiates the formation of C3b)
20 Aug 2012

Is C3b an opsonin? ›

The C3b is said to be acting as an opsonin in this case because it enhances the ability of an entity to be phagocytosed. By encouraging pathogen uptake by APCs in this way, C3b indirectly enhances antigen presentation to T cells and thus the adaptive response.

What is opsonin dependent? ›

In opsonin-dependent phagocytosis, antibody or complement opsonizes the pathogen and promotes its phagocytosis via Fcγ or complement receptors on phagocytes.

What are opsonins a level biology? ›

Opsonins: ​Chemicals that bind to and tag foreign cells, making them easily recognisable to phagocytes. Passive immunity: ​Resistance in an organism acquired via the transfer of antibodies. It provides short-term immunity as no memory cells are produced. Pathogen: ​A disease-causing microorganism.

Is complement an opsonin? ›

Complement protein mediated opsonization

C3b, C4b, and C1q are important complement proteins that mediate opsonization. As a part of the alternative complement pathway, the spontaneous activation of a complement cascade converts C3 to C3b, a component that can serve as an opsonin when bound to an antigen's surface.

Is C3a an opsonin? ›

Here they cleave C3 to generate large amounts of C3b, the main effector molecule of the complement system, and C3a, a peptide mediator of inflammation. The C3b molecules act as opsonins; they bind covalently to the pathogen and thereby target it for destruction by phagocytes equipped with receptors for C3b.

Is IgA an opsonin? ›

Whereas IgG efficiently opsonizes pathogens for engulfment by phagocytes and activates the complement system, IgA is a less potent opsonin and a weak activator of complement.

What is the role of opsonins quizlet? ›

What is the role of opsonins? They create "handles" that make it easier for the pseudopods of phagocytes to attach to the microbe invader. They are present on the surface of phagocytes.

Is opsonization a function of antibodies? ›

Another mechanism by which antibodies can response to pathogens is known as “opsonization.” By opsonization, antibodies enable phagocytes for ingesting and destroying the extracellular bacterium. The phagocytes recognize the Fc region of the antibodies coating the pathogen and foreign particles (Fig.

What are the 3 main functions of the complement system? ›

At the basic level the broad functions of the complement system can be split into three areas: (1) the activation of inflammation; (2) the opsonization (labeling) of pathogens and cells for clearance/destruction; (3) the direct killing of target cells/microbes by lysis.

What are the 3 complement pathways? ›

The complement pathway. Complement can be activated through three pathways: classical, lectin, and alternative. The classical pathway is activated when C1q binds to antibody attached to antigen, activating C1r and C1s, which cleave C4 and C2.

How many types of antibodies show opsonization? ›

2) The antibodies bind to pathogens, and can do so in different formations such as: opsonization (2a), neutralisation (2b), and agglutination (2c).

Which is strongest opsonin? ›

C3b is by far the most effective opsonin that initiates phagocytosis as it can be recognized by phagocyte receptors.

Is C3 an opsonin? ›

We conclude that two fragments of the C3 molecule, that is, C3b and C3d, can function as opsonins if the phagocyte has the appropriate membrane receptors. Monocytes, that bind both C3b and C3d, respond to both as opsonins.

Where is opsonin? ›

Opsonins are freely circulating serum molecules which are produced to attach to the surface of microbes, so rendering them more attractive to phagocytes. The process of coating a particle with opsonins is called opsonization.

Is opsonin a plasma component? ›

Overview of Serum Opsonins

These heat-labile and heat-stable plasma proteins, called opsonins, consist mainly of serum antibodies and components of the complement system, although several other proteins seem to play important roles (see later).

How do you pronounce opsonin? ›

How To Say Opsonins - YouTube

Where is C3b found? ›

C3b-coated particles in the blood mainly bind to red blood cells, which have the receptor CR1 that binds C3b. C3b is gradually converted to iC3b. iC3b binds only weakly to CR1, but binds strongly to CR3 and CR4, which are found on phagocytic cells.

Is C3b a protein? ›

It is a complex protein, which generates different functional activated fragments (C3a, C3b, iC3b, C3c, C3d). C3b is a constituent of the alternative pathway C3 convertase (C3bBb), binds multiple regulators, and receptors, affecting thus the functioning of the immune system.

Does C5a act as opsonin? ›

We conclude that C5a enhances phagocytosis of opsonized liposomes by activating the phagocytic capacity of CR3 on the PMN.

Which antibodies do opsonization? ›

Opsonization of bacteria takes place when immunoglobulin G (IgG) molecules bind to specific epitopes on bacterial surface antigens through the antigen-binding site of the IgG molecule.

What is opsonization quizlet? ›

opsonization. The coating of an antigen or particle (eg, infectious agent) by substances, such as antibodies, complement components, fibronectin, and so forth, that facilitate uptake of the foreign particle into a phagocytic cell. Respiratory Burst.

What is opsonization and how does it help phagocytes give an example of a molecule that acts as an opsonin? ›

Opsonization is the process of making pathogens more susceptible to phagocytosis by decorating their surface with molecules that phagocytes can bind. Antibodies and complement proteins are examples of molecules that act a opsonin.

What is opsonization and why is it important? ›

Opsonization is the important process in host defense by which particles or complexes are made readily ingestible for uptake by phagocytic cells. Specific serum proteins, known as opsonins, coat particles and cause the particles to bind avidly to phagocytes and trigger ingestion.

Which is strongest opsonin? ›

C3b is by far the most effective opsonin that initiates phagocytosis as it can be recognized by phagocyte receptors.

Is C3b an opsonin? ›

The C3b is said to be acting as an opsonin in this case because it enhances the ability of an entity to be phagocytosed. By encouraging pathogen uptake by APCs in this way, C3b indirectly enhances antigen presentation to T cells and thus the adaptive response.

Is IgM and opsonin? ›

Antibody mediated opsonization

Phagocytic cells do not have an Fc receptor for immunoglobulin M (IgM), making IgM ineffective in assisting phagocytosis alone. However, IgM is extremely efficient at activating complement and is, therefore, considered an opsonin.

What is Opsonization In microbiology quizlet? ›

1) Opsonization: coating of bacteria with antibody to enhance. phagocytosis. 2) Complement activation: antibody binding triggers classical.

Which of the following is not a mechanical barrier against microorganism? ›

A&PII
QuestionAnswer
which of the following is not a mechanical barrier against microorganisms?diarrhea
___ initiate(s) a cascade effect in response to foreign proteins in the body.the complement system
66 more rows

How does Opsonization help enhance phagocytosis quizlet? ›

Opsonization: Coats pathogen surfaces which enhances phagocytosis. Enhances inflammation: Stimulates histamine release. Activates proteins to bind to target cell membrane creating a pore that can lyse the target cell.

What molecules are opsonins? ›

An opsonin is any molecule that acts as a binding enhancer for the process of phagocytosis, for example, by coating the negatively-charged molecules on the membrane.
...
Examples
  • antibodies: IgG and IgA.
  • components of the complement system: C3b, C4b, and iC3b.
  • Surfactant.
  • Mannose-binding lectin (initiates the formation of C3b)
20 Aug 2012

What molecules act as opsonins? ›

Examples of opsonins include IgG antibody - part of the immune response - and the C3b molecule of the complement system. Each has receptors for both foreign particle and host phagocyte.

Are opsonins antibodies? ›

Antibodies are important opsonins in their own right, but they also facilitate more rapid complement activation and more effective localization of C3b binding to the surface of the organism.

What is opsonin dependent? ›

In opsonin-dependent phagocytosis, antibody or complement opsonizes the pathogen and promotes its phagocytosis via Fcγ or complement receptors on phagocytes.

What is the role of opsonization In phagocytosis? ›

Phagocytosis: Opsonization - YouTube

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