Cytokines Definition

Cytokines are tiny protein molecules that help cells communicate with one another. They can tell cells where to go and what to do. The body depends on cytokines to initiate and regulate:

  • Immune system responses, including inflammation
  • The production of blood cells
  • Tissue repair

This page explains how cytokines work and their involvement in autoimmune diseases and treatments.

  • Cytokines are produced and released by cells located throughout the body, including but not limited to:
    • White blood cells, such as macrophages, B and T lymphocytes, and mast cells
    • Endothelial cells, which line the blood vessels (arteries, veins, and capillaries)
    • Fibroblasts, which are found in connective tissues, such as skin, tendon, and joint lining
  • A cell can produce more than one type of cytokine. Similarly, many types of cells can produce the same cytokine.
  • A cytokine must attach itself to a cell in order to deliver its signal. It does so by binding to a cell’s cytokine receptor, typically located on the surface of the cell.
  • A cytokine may bind to a receptor on:
    • The same cell that produced it (autocrine action)
    • A nearby cell (paracrine action)
    • A faraway cell reached through the bloodstream (endocrine action)
  • Once a cytokine is bound to a cell, it will activate specific genes in the cell, essentially giving the cell specific instructions. The instructions may prompt the cell to:
    • Reproduce
    • Die
    • Perform a specific job, such as attacking an infectious bacterium or viral

A cytokine may have the potential to signal different messages, and it may be pro-inflammatory or anti-inflammatory. What a particular cytokine does depends on many factors. Researchers are still learning about these processes.

Cytokines and autoimmune disease

Cytokines affect how intense and how long an immune system response will be. In people with certain conditions, such as allergies and autoimmune disease, cytokines cause the immune system to over-react.

For example, experts believe that rheumatoid arthritis symptoms occur when the cells in a joint’s lining (synovium) secrete proinflammatory cytokines. These cytokines, such as interleukin-1 (IL-1), TNF-α, and IL-6,1 lead to joint inflammation and tissue destruction.2

Cytokines and biologic medications

Autoimmune diseases, such as rheumatoid arthritis and psoriatic arthritis, may be treated with biologic medications that target cytokines.

Biologics work by attaching to proinflammatory cytokines and preventing them from binding to cell receptors. For example, etanercept, infliximab, adalimumab, certolizumab pegol, and golimumab are all biologic medications that target TNF-α.

See Biologics: Basic Facts for Patients

Cytokine storm

During a cytokine storm, the body is fighting off an infection and cells make too many cytokines. This overproduction causes the body to sense something is wrong, and cells react by producing even more cytokines. This cascading immune response causes immune cells to attack organs, leading to organ damage and possible death.

A cytokine storm may be triggered by various types of infections, including Covid-19, as well as other medical conditions and even certain therapies, such as stem cell transplants.

A cytokine storm is different than an autoimmune disease flare-up, such as a rheumatoid flare that causes joint inflammation and fatigue. The production of cytokines is more out of control during a cytokine storm.

Cytokines vs. hormones

Both cytokines and hormones communicate with cells to trigger action. While they are often compared, cytokines and hormones are different in two ways:

  1. They tend to be different in size, shape, and weight.
  2. Cytokines are produced by cells located throughout the body, while hormones are generally produced by glands, such as the thyroid, adrenal, and pituitary glands.

Cytokines are constantly at work in the body. Researchers are still learning about cytokines and their role in health and disease processes as well as potential treatments.

References

  • 1.Benjamin IJ, Griggs RC, Wing EJ, & Fitz JG. Andreoli and Carpenter's Cecil Essentials of Medicine, 9th edition. 2016. Elsevier/Saunders.
  • 2.Kennedy A, Fearon U, Veale DJ, Godson C. Macrophages in synovial inflammation. Front Immunol. 2011;2:52. Published 2011 Oct 10. doi:10.3389/fimmu.2011.00052