Cytokines are small proteins that cells release to send signals to other cells. They act as messengers of the immune system, telling cells when to activate, where to go, how fast to multiply, and when to die. The term itself comes from the Greek words for “cell” and “movement,” coined by scientist Stanley Cohen in 1974. Though they’re most famous for their role in immunity and inflammation, cytokines influence everything from wound healing to fever to pain sensitivity.
How Cytokines Work
Think of cytokines as chemical text messages between cells. One cell releases a cytokine into its surroundings, and nearby cells (or sometimes distant cells) pick up that signal through specialized receptors on their surface. When a cytokine locks onto its receptor, it triggers a chain reaction inside the receiving cell that changes its behavior.
These signals travel at three different ranges. Sometimes a cell sends a cytokine message to itself, adjusting its own activity. Other times, cytokines travel short distances to communicate with neighboring cells in the same tissue. In some situations, cytokines enter the bloodstream and affect cells far from their origin, similar to how hormones work. This flexibility is what makes cytokines so central to the body’s ability to coordinate complex responses like fighting an infection or repairing damaged tissue.
Which Cells Produce Them
Many cell types can release cytokines, but the biggest producers are two workhorses of the immune system: helper T cells and macrophages. Helper T cells act as coordinators of immune responses, while macrophages are large cells that engulf and destroy invaders. Together, they pump out cytokines to rally other immune cells into action.
Cytokines aren’t exclusive to immune cells, though. Cells lining blood vessels, connective tissue cells called fibroblasts, and even nerve-supporting cells all produce cytokines under certain conditions. This is why inflammation and pain signaling can happen in tissues throughout the body, not just where immune cells are concentrated.
Pro-Inflammatory vs. Anti-Inflammatory
Cytokines fall into two broad camps based on their effect on inflammation. Pro-inflammatory cytokines are the alarm bells. When you get an infection or an injury, cytokines like IL-1 beta, IL-6, and TNF-alpha kick the immune system into high gear. They recruit white blood cells to the site of trouble, trigger fever, cause swelling, and increase pain sensitivity. TNF-alpha, for example, directly sensitizes nerve cells and amplifies pain signals by releasing inflammatory compounds like prostaglandins. IL-6 works alongside it, boosting the production of other inflammatory cytokines and heightening sensitivity to touch and temperature.
Anti-inflammatory cytokines do the opposite. IL-10, IL-4, and IL-13 act as brakes on the immune response, suppressing the production of pro-inflammatory signals and promoting tissue repair. IL-10 is one of the most powerful: it blocks the production of several major inflammatory cytokines at once. The body also produces IL-1 receptor antagonist, a molecule that physically blocks inflammatory IL-1 from binding to cells. Health depends on the balance between these two groups. Too much inflammation causes tissue damage; too little leaves you vulnerable to infection.
The Major Families
Scientists have identified dozens of individual cytokines, grouped into several major families based on their structure and function.
- Interleukins are the largest group, numbered sequentially (IL-1, IL-2, IL-3, and so on). They handle a wide range of jobs, from activating white blood cells to suppressing inflammation. Some promote the growth of new blood cells in bone marrow.
- Interferons are the body’s primary antiviral defense. Type I interferons respond rapidly when cells detect a virus, while type II interferon activates macrophages and drives inflammatory immune responses.
- Tumor necrosis factors specialize in triggering cell death. TNF-alpha is a major driver of inflammation in conditions like rheumatoid arthritis and inflammatory bowel disease. Another family member, FasL, helps the immune system eliminate defective or unnecessary cells.
- Chemokines are “homing signals” that guide immune cells toward infection or injury sites, essentially creating a chemical trail for white blood cells to follow.
- TGF-beta is unusual because it can either promote or suppress inflammation depending on the context. It plays a key role in controlling immune responses and orchestrating tissue repair.
What a Cytokine Storm Is
A cytokine storm happens when the body’s inflammatory response spirals out of control. Instead of a targeted, proportional immune reaction, the body floods itself with pro-inflammatory cytokines, which recruit even more immune cells, which release even more cytokines. This feedback loop can cause widespread tissue damage, organ failure, and in severe cases, death.
Cytokine storms have been documented in infections with influenza, Epstein-Barr virus, and SARS coronaviruses, which is why COVID-19 drew so much attention to this phenomenon. They also occur in non-infectious contexts: certain cancer immunotherapies (CAR-T cell therapy) can trigger cytokine release syndrome, and bone marrow transplant patients sometimes experience it as part of graft-versus-host disease. The lungs are especially vulnerable, with acute respiratory distress syndrome being one of the most dangerous consequences.
Cytokines in Medicine
Because cytokines are so central to immune function, they’ve become both tools and targets in modern medicine. Some treatments use lab-made versions of cytokines directly. A synthetic form of IL-2, for instance, is used to treat advanced kidney cancer and melanoma by supercharging the immune system’s ability to attack tumor cells.
More commonly, treatments work by blocking specific cytokines. A synthetic IL-1 receptor antagonist is used to treat rheumatoid arthritis and a group of inherited inflammatory conditions by preventing IL-1 from triggering inflammation. TNF-alpha blockers are among the most widely prescribed biologic drugs, used for autoimmune conditions where excessive inflammation drives symptoms.
Measuring cytokine levels in blood can help doctors assess the severity of infections, track autoimmune disease activity, and evaluate how well treatments are working. The standard method uses a technique called ELISA, though newer technologies can now measure panels of many cytokines simultaneously from a small blood sample. These measurements are most useful for research and tracking trends over time rather than as standalone diagnostic tests.
Why Cytokines Matter for Everyday Health
Every time you run a fever, feel achy during the flu, notice swelling around a cut, or experience joint stiffness from an autoimmune condition, cytokines are driving those sensations. Fever is triggered by IL-1 and IL-6 acting on the brain’s temperature control center. The soreness you feel during an infection comes from TNF-alpha and IL-6 sensitizing your pain receptors. The redness and warmth around a healing wound reflect cytokines directing blood flow and immune cells to the area.
Chronic low-grade inflammation, which is linked to conditions like heart disease, type 2 diabetes, and depression, also involves sustained elevation of pro-inflammatory cytokines. This is one reason lifestyle factors like sleep, exercise, and diet matter for long-term health: they influence the baseline levels of these signaling molecules circulating in your body.