What is the Difference Between Opsonization and Phagocytosis

The main difference between opsonization and phagocytosis is that opsonization is the mechanism that targets particles for destruction by phagocytosis, while phagocytosis is the process by which the plasma membrane engulfs large particles, forming phagosomes. 

Opsonization and phagocytosis are two critical processes in adaptive immunity. They occur in antigen-presenting cells.  

Key Areas Covered

1. What is Opsonization
– Definition, Features, Importance
2. What is Phagocytosis
– Definition, Features, Importance
3. Similarities Between Opsonization and Phagocytosis
– Outline of Common Features
4. Difference Between Opsonization and Phagocytosis
– Comparison of Key Differences

Key Terms 

Opsonization, Phagocytosis

What is Opsonization 

Opsonization is an immunological process that recognizes, targets, and invades particles for phagocytosis. Importantly, opsonization uses opsonin, such as complement C3b and antibodies, to tag pathogens for elimination by phagocytosis. Otherwise, the pathogen’s and pphagocyte’s negatively-charged cell walls repel each other. Plasma cells of the immune system produce antibodies as a part of the adaptive immune system. Antibodies are complex structures with specificity to a particular antigen because different antigens produce different antibodies. These antibodies have variable regions to bind to specific epitopes in the antigen. Upon binding to pathogens, the stem region of the antibody is capable of binding to the cell membrane of phagocytes.

Figure 1: Opsonization

Furthermore, the binding of multiple antibodies to multiple sites of the antigen increases the chance of the engulfing of the antigen by a phagocyte. The complement system also contains more than 30 types of proteins that can serve as opsonins. These proteins improve the ability to bind antibodies to antigens. 

What is Phagocytosis

Phagocytosis is the process of multicellular organisms that use plasma membrane to engulf large particles, which are more than 0.5 μm. During phagocytosis, the cell takes up particles like debris, aged cells, tiny mineral particles, dust, various colloids, and bacteria. The immune system cells, like tissue macrophages, neutrophils, and monocytes, use phagocytosis to engulf cells. Phagocytic cells also occur in Langerhans cells in the skin, Kupffer cells in the liver, the pigmented epithelium of the eye, and the microglia in the brain. Phagocytosis is essential in defense mechanisms that destroy pathogenic material found in the body. It is also a receptor-mediated process. Some receptors important in this process are immunoglobulin G, mannose (MR), β-glucan, and complement (CR1, CR3).

Figure 2: Phagocytosis

Furthermore, surrounding the particle to be uptaken, the phagocytic cells form pseudopodia. Then, the plasma membrane pinches off into a phagocytic vesicle or a phagosome. Phagosomes can fuse with lysosomes, creating the phagolysosomes—moreover, the enzymes inside the phagolysosome help to digest the materials inside the phagosome. After digestion, the waste materials eliminate through exocytosis. Phagocytosis is a cell-eating mechanism.

Similarities Between Opsonization and Phagocytosis

• Opsonization and phagocytosis are two processes in the immune system.
• They engulf foreign particles, such as pathogens.
• They occur in antigen-presenting cells. 

Difference Between Opsonization and Phagocytosis

Definition

Opsonization refers to the process or molecular mechanism that uses opsonins to make a molecule (e.g., antigen) palatable to the phagocyte. In contrast, phagocytosis involves ingesting bacteria or other material by phagocytes and amoeboid protozoans.

Significance

Opsonization is the mechanism that targets particles for destruction by phagocytosis, while phagocytosis is the process by which the plasma membrane engulfs large particles, forming phagosomes. 

Type of Process

Opsonization is an immunological process, while phagocytosis is an immunological process in multicellular organisms. 

Conclusion

In brief, opsonization and phagocytosis are two types of immune system processes involving engulfing foreign particles such as bacteria. Opsonization is the immunological process that targets foreign particles for destruction by phagocytosis. In comparison, phagocytosis is another immunological process in multicellular organisms to engulf foreign particles and destroy them with digestive enzymes inside the cell. Therefore, the main difference between opsonization and phagocytosis is the mechanism of the process. 

References:

1. Thau L, Asuka E, Mahajan K. Physiology, Opsonization. [Updated 2023 May 1]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-.
2. Rosales C, Uribe-Querol E. Phagocytosis: A Fundamental Process in Immunity. Biomed Res Int. 2017;2017:9042851. doi: 10.1155/2017/9042851. Epub 2017 Jun 12. PMID: 28691037; PMCID: PMC5485277.

Image Courtesy:

1. “Antigen-antibody interactions (opsonization) ku.” By https://openstax.org – Own work (CC-BY 4.0) via Commons Wikimedia
2. “Phagocytosis — amoeba” By Kate Taylor – Own Work (CC0) via Commons Wikimedia