• A class of soluble glycoproteins which act nonenzymatically through specific receptors to regulate immune responses. Cytokines are derived from both immune and non-immune cells and are intercellular mediators that differ from hormones in that they are produced by a number of tissue or cell types rather than by specialized glands.
  NCI
  U.S. National Cancer Institute, 2021
• A substance that is made by cells of the immune system. Some cytokines can boost the immune response and others can suppress it. Cytokines can also be made in the laboratory by recombinant DNA technology and used in the treatment of various diseases, including cancer.
  NCI Dictionary of Cancer Terms
  U.S. National Cancer Institute, 2021
• Soluble factors elaborated by cells of the immune system that act on other cells to regulate their function.
  CRISP Thesaurus
  National Institutes of Health, 2006
• Non-antibody proteins secreted by inflammatory leukocytes and some non-leukocytic cells, that act as intercellular mediators. They differ from classical hormones in that they are produced by a number of tissue or cell types rather than by specialized glands. They generally act locally in a paracrine or autocrine rather than endocrine manner.
  NLM Medical Subject Headings
  U.S. National Library of Medicine, 2025
• Proteins in the body that act as messengers between immune system cells.
  Harvard Dictionary of Health Terms
  Harvard Medical Publishing, 2011
• Cytokine, any of a group of small, short-lived proteins that are released by one cell to regulate the function of another cell, thereby serving as intercellular chemical messengers. Cytokines effect changes in cellular behaviour that are important in a number of physiological processes, including...
  Encyclopedia Britannica
  Encyclopedia Britannica, Inc., 2025