OPSONIZATION: WHAT IT CONSISTS OF, TYPES AND FUNCTIONS - BIOLOGY - 2025

The opsonization is a cellular phenomenon increases the efficiency of phagocytosis. To achieve this, the presence of special elements called opsonins is necessary, which are antibodies or other molecules that have the capacity to adhere to the surface of the cell of the microbe that must be destroyed.

Thus, the presence of opsonins on the surface of the pathogen or microbial agent makes the phagocytosis process more efficient and faster, promoting the recognition and destruction of the microbe. As a consequence, the number of phagocytosed microbes also increases.

1) Antibodies (A) and pathogens (B) roam freely in the blood. 2) 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) Finally, phagocytosis occurs as the pathogen is ingested.

Source: Maher33

There are different types of opsonins. In fact, this group of molecules is made up of a fairly wide and heterogeneous series of biological entities belonging to the immune system or the complement system.

When the body undergoes inflammatory processes, the number of phagocytic cells increases significantly, compared to the usual residents of the tissue. In addition, there are another series of changes: cells are much more active to chemotactic stimuli. With the presence of opsonins, all these processes enhance their efficiency.

What is opsonization?

It is the process of binding molecules called opsonins to pathogens, which increase the efficiency of phagocytosis. Opsonization is a process of great importance in the field of immunology, since it actively participates in infection control.

Phagocytosis occurs through monocytes and macrophages, cells that are part of the mononuclear phagocytic system. The mentioned cells are capable of consuming or ingesting elements from a medium that undergoes an inflammatory process. These cells are abundant in the blood and in various tissues.

Phagocytosis is a process that is divided into several stages: activation, chemotaxis, recognition and adherence, ingestion, death and digestion, and expulsion.

Opsonization is key in the recognition stage, since opsonins allow the formation of a bridge between the phagocyte and the bacteria that will be phagocytosed.

Opsonins

Opsonins are the molecules involved in the opsonization process. Biochemically and structurally, they are made up of an immense variety of molecules from the immune system and the complement system.

The most important ones are called immunoglobulins G, in their Fc portion, the activated C3b portion of the complement and lectins. There are also tufsin, serum amylode P protein, among others. We will clarify the use of these terms later.

Types of opsonization

Opsonization is divided into two main types: immune and non-immune. This classification is based on the type of opsins that participate.

Immune opsonization

To understand this type of opsonization, we must know certain aspects related to the immune response. The complement system is one of the essential components of the inflammatory response to the presence of some microorganism or pathogen.

It is made up of a set of plasma molecules that participate in biochemical pathways that enhance inflammation and facilitate phagocytosis. Specifically, it is made up of about 30 glycoproteins.

Phagocytes, like macrophages, monocytes, and neutrophils, possess on their cell membranes a series of receptors (called CR1) for C3b and Fc for the antibody.

C3b is a component of the complement system mentioned above. Fc (crystallizable fragment), for its part, is a portion of the antibody made up of two or three domains of heavy chains.

A typical antibody is made up of a basic structure. In turn, it is made up of so-called heavy chains and light chains, two of each type.

In the event that the immune system has activated the complement system, the existing Fc and CR1 receptors on the phagocyte bind to the Fc regions of the antibody and C3b binds to the immune complex, facilitating phagocytosis. How antibody and complement elements participate is called immune opsonization.

Non-immune opsonization

This type of opsonization is similar to that described above, with the only exception that the process component is only opsonin C3b. The alternative pathway can be activated by bacteria in the blood and generate C3b, which surrounds the bacteria.

C3b binds to CR1 receptors located on phagocytes, thus facilitating phagocytosis. The different complexes that are soluble, viruses and cells with tumor characteristics are also opsonized and removed by this mechanism.

Bodies involved

Opsonization occurs in the immune system and the organs involved are dependent on the mechanism used.

The lymphatic system is responsible for the transport and filtration of lymphatic fluids that contain lymphocytes and antibodies. The cardiovascular system is responsible for orchestrating the circulation of blood through the body, which is necessary for the complement system pathway.

The lectin system requires the additional involvement of the liver, an organ that is part of the gastrointestinal system. All of the aforementioned systems work together to fight bacteria, viruses, and other invaders that try to attack the body.

Function of opsonization

The human body is continually being attacked by external agents. Fortunately, attempts by pathogens to hijack the cellular machinery are countered by elements of the immune system. There are different mechanisms in charge of countering these attacks, and one of them is opsonization.

Opsonization is a process that facilitates the phagocytosis of pathogens or external agents (such as bacteria or parasites, for example) that enter the body and that can have potential negative consequences. For this reason, it is an important phenomenon in the immune response.

To understand its function, we must know the structure of the pathogen's surface. Generally, the capsules of various bacteria are negatively charged, which greatly prevents interaction with the cell that will engulf it.

When the pathogen undergoes opsonization, the rapprochement between the cell of the immune system and the bacteria is favored by creating a very close connection between both.

If opsonin were not present, the negative charges on the cell wall of the pathogen and phagocyte would repel each other. In this way, the pathogen would be able to evade destruction and could continue the invasion of the human body.

Thus, opsonins help overcome electrostatic forces, allowing the elimination of the microbe.

References

1. Avery, GB, & Fletcher, MA (2001). Neonatology: pathophysiology and management of the newborn. Panamerican Medical Ed.
2. Cabello, RR (2007). Human microbiology and parasitology: Etiological bases of infectious and parasitic diseases. Panamerican Medical Ed.
3. Hostetter, MK, Krueger, RA, & Schmeling, DJ (1984). The biochemistry of opsonization: central role of the reactive thiolester of the third component of complement. Journal of Infectious Diseases, 150 (5), 653-661.
4. Ingraham, JL, & Ingraham, CA (1998). Introduction to Microbiology (Vol. 2). I reversed.
5. Kumar, S. (2012). Textbook of microbiology. JP Medical Ltd.
6. López, LR, & López, MCL (1993). Molecular parasitology (Vol. 24). Editorial CSIC-CSIC Press.
7. Wilson, CB, Nizet, V., Remington, JS, Klein, JO, & Maldonado, Y. (2010). Infectious diseases of the fetus and newborn E-Book. Elsevier Health Sciences.