What is the Difference Between Cytokines and Opsonins

The key difference between cytokines and opsonins is that cytokines are small extracellular proteins that participate in cell signalling, while opsonins are large extracellular proteins that bind to cells and induce phagocytosis.

Cytokines and opsonins are two different types of proteins that participate in cell communication. Generally, cells communicate with each other by using chemical signals. These chemical signals are usually proteins or other molecules. Message sending cells produce these proteins and other molecules and often secrete them into the extracellular space. They can float in the extracellular space and carry messages from the message sending cells to target cells. Based on these messages, the neighbouring cells generate responses.

CONTENTS

1. Overview and Key Difference
2. What are Cytokines
3. What are Opsonins
4. Similarities – Cytokines and Opsonins
5. Cytokines vs Opsonins in Tabular Form
6. Summary – Cytokines vs Opsonins

What are Cytokines?

Cytokines are a broad and loose category of small proteins that participate in cell signalling. They have a molecular weight of 5 to 20 kDa. Cytokines are peptides. They cannot cross the lipid bilayer of cells and enter into the cytoplasm. As immunomodulating agents, cytokines are involved in autocrine, paracrine, and endocrine signalling. However, they are different from hormones or growth factors. Cytokines normally include chemokines, interferons, lymphokines, and tumor necrosis factors. Cytokines are produced by a wide range of cells, including macrophages, B lymphocytes, T lymphocytes, mast cells, endothelial cells, fibroblasts, and stromal cells. Moreover, cytokines can be produced by more than one type of cell.

Cytokines act through binding to cell surface receptors. They are especially important for a fully functional immune system. In the immune system, cytokines regulate the balance between humoral and cell-based immune responses. Cytokines also trigger the maturation, growth and responsiveness of a particular cell population in the immune system. Furthermore, cytokines can enhance or inhibit other cytokines in a metabolic reaction pathway. Cytokines are also very important in host responses in diseases. They can become dysregulated in pathological conditions such as inflammation, trauma, sepsis, and haemorrhagic stroke, etc. Recombinant cytokines have been used over the years in medicine as drugs.

What are Opsonins?

Opsonins are large extracellular proteins that bind to cells and induce phagocytosis. These proteins act as tags to label things such as pathogens in the body that should be phagocytosed. Therefore, phagocytic cells can easily eat up these foreign pathogens and protect the body from infections. Opsonins generally tag different types of targets, including bacteria, cancer cells, aged cells, dead or dying cells, excess synapses, or protein aggregates. Therefore, opsonins help to clear out pathogens as well as dead, diseased or dying cells.

Opsonin was first discovered by Wright and Douglas in 1904. Wright and Douglas found that incubating bacteria with blood plasma enabled phagocytic cells to phagocytose the bacteria. Broad research found two main types of opsonins in blood: complement proteins and antibodies. However, there are around 50 different proteins that can act as opsonins for different pathogens and other targets.

What are the Similarities Between Cytokines and Opsonins?

• Cytokines and opsonins are proteins that participate in cell communication.
• Both are extracellular proteins.
• They bind to cell surface receptors.
• They are important components of the immune system.
• They help to remove pathogens from the body and protect the body against various diseases.

What is the Difference Between Cytokines and Opsonins?

Cytokines are small extracellular proteins that participate in cell signalling, while opsonins are large extracellular proteins that bind to cells and induce phagocytosis. So, this is the key difference between cytokines and opsonins. Furthermore, the size of cytokine is around 5-20 kDa, while the size of opsonin is around 150-400 kDa. Thus, this is another difference between cytokines and opsonins.

The below infographic lists the differences between cytokines and opsonins in tabular form for side by side comparison.

Summary – Cytokines vs Opsonins

Cytokines and opsonins are two proteins that are extremely important for the immune system. They participate in cell communication. Cytokines are small extracellular proteins that participate in cell signalling, while opsonins are large extracellular proteins that bind to cells and induce phagocytosis. Thus, this is the key difference between cytokines and opsonins.

Reference:

1. Zhang, Jun-Ming, and Jianxiong An. “Cytokines, Inflammation, and Pain.” International Anesthesiology Clinics, U.S. National Library of Medicine, 2007.
2. “Opsonins.” An Overview | ScienceDirect Topics.

Image Courtesy:

1. “Fimmu-11-01648-g002” By Sonu Bhaskar, Akansha Sinha, Maciej Banach, Shikha Mittoo, Robert Weissert, Joseph S. Kass, Santhosh Rajagopal, Anupama R. Pai, and Shelby Kutty – Bhaskar S, Sinha A, Banach M, Mittoo S, Weissert R, Kass JS, Rajagopal S, Pai AR and Kutty S (2020) Cytokine Storm in COVID-19—Immunopathological Mechanisms, Clinical Considerations, and Therapeutic Approaches: The REPROGRAM Consortium Position Paper. Front. Immunol. 11:1648.https://doi.org/10.3389/fimmu.2020.01648 (CC BY 4.0) via Commons Wikimedia
2. “Antibody Opsonization” By Maher33 – Own work (CC BY-SA 4.0) via Commons Wikimedia