Cytokines

What are cytokines?

Cytokines are proteins that function as chemical messengers in your immune system. Your immune system is a network with several parts that work together to protect your body from threats, like germs that can make you sick. It contains immune cells that fight invading pathogens (like viruses and bacteria), allergens and other harmful substances that enter your body. Cytokines signal those immune cells to fight the invaders.

Even when there’s no threat, cytokines send signals to other cells that keep your immune system functioning.

What are the different types of cytokines?

Cytokines include different types of proteins that tell immune cells where to go and what to do to keep your immune system functioning correctly.

• Chemokines: Chemokines direct immune cells toward places in your body where they can fight infection.
• Interferons: Interferons signal cells to put up their defenses against viruses invading your body. In this way, interferons “interfere” in the process that allows viruses to replicate, or make more viruses once they’ve invaded a healthy cell.
• Interleukins: Interleukins get their name from “inter” which means between and “leukocyte,” which is another name for a white blood cell. Originally, scientists thought that leukocytes alone released interleukins and only relayed messages to other leukocytes. But now we know that cells other than leukocytes release these proteins. Also, interleukins can relay messages between cells that aren’t leukocytes.
• Tumor necrosis factor (TNF): TNF helps regulate inflammation in your body. TNF also signals to immune cells that kill tumor cells.
• Colony-stimulating factors (CSF): CSF signals hematopoietic stem cells to develop into specific cell types. Hematopoietic stem cells (HSC) are precursor cells that give rise to all blood cell types: white blood cells, red blood cells and platelets. These changes take place during a process called hematopoiesis. For example, granulocyte-colony stimulating factor (G-CSF) signals an HSC to become a white blood cell called a neutrophil. Neutrophils help fight infection.

Some cytokines get their names from the type of cell that makes them, including:

• Lymphokines: Produced by lymphocytes, a type of white blood cell.
• Monokines: Produced by monocytes, a type of white blood cell.

What do cytokines do?

Cytokines are most known for regulating inflammation in your body. Many people think of inflammation as a pesky symptom that means you’re sick or have allergies. But inflammation is a sign that your body’s immune cells are fighting invaders or healing tissue damage. Your body’s cells release cytokines when there’s a threat. The cytokines tell your immune cells how to fight threats and repair injuries.

Think of cytokines as chemical messengers that tell cells how to behave.

Cytokines signal:

• Cell activation: Cytokines tell cells where to go and what to do. For example, cytokines can direct immune cells toward an infection site so the cells can fight germs there. They can heighten or lessen the processes associated with inflammation.
• Cell differentiation: Cytokines can tell immature cells to develop into a specific type of cell. For example, cytokines can tell an immature cell to mature into a white blood cell capable of fighting infection.
• Cell proliferation: Cytokines can tell a cell to make more cells just like it. For example, cytokines can tell a white blood cell to make more white blood cells to fight infection.

Cytokines can also signal your body’s cells to release more cytokines to increase your body’s inflammatory response.

What’s the difference between pro-inflammatory and anti-inflammatory cytokines?

When your body’s immune response is working correctly, cytokines trigger inflammation that helps fight threats and repair tissue. Cytokines also decrease or stop your body’s inflammatory response when you no longer need it.

• Pro-inflammatory cytokines trigger or heighten inflammation. They relay messages that coordinate your body’s immune response to fend off attackers, like germs.
• Anti-inflammatory cytokines stop or lessen inflammation. They relay messages that prevent an excessive immune response that can lead to tissue damage.

Stopping your body’s inflammatory response is just as important as starting it. Too much inflammation can cause unpleasant symptoms, lead to long-term diseases and can even be life-threatening without treatment.

How do cytokines work?

Certain cells release cytokines while other cells contain cytokine receptors. Think of a cytokine as a key and the receptor on the receiving cell like a lock. When the cytokine (key) enters the cytokine receptor (lock), the receiving cell receives a message that tells it what to do. The cell acts based on the message it receives.

For example, an immune cell may detect a harmful substance in your body, like a virus, and release cytokines in response. Cytokines can travel through your bloodstream or directly into tissue until they reach a cell with the matching receptor. Once the cytokine binds to the receptor, the receiving cell receives instructions and acts on them. For instance, the cell may travel to the virus and attack it. It may increase its defenses to prevent viruses from invading.

Cytokines may signal cells close to the cell that released them, or they can travel great distances to relay their message.

• Autocrine signaling: Cytokines can bind to receptors on the same cell that released it.
• Paracrine signaling: Cytokines can bind to receptors on nearby cells.
• Endocrine signaling: Cytokines can bind to receptors on cells located far away from the cell that released the cytokines.

Cells with cytokine receptors are located throughout your body. In fact, most of your body’s organs contain cells with cytokine receptors. Having cells with cytokine receptors throughout your body allows inflammation to occur in widespread locations.

Where do cytokines come from?

The cells that make up your immune system, or immune cells, release most of your body’s cytokines. Still, many cells throughout your body — not just immune cells — can release cytokines.

Immune cells

Immune cells include your body’s white blood cells, also called leukocytes. Immune cells that release cytokines include:

• Macrophages.
• Dendritic cells.
• Lymphocytes (T and B lymphocytes).
• Monocytes.
• Neutrophils.
• Basophils.
• Eosinophils.
• Mast cells.

Other cells

Cells that aren’t considered immune cells that also release cytokines include:

• Endothelial cells (cells that line the inside of your blood vessels).
• Epithelial cells (cells that line your organs).
• Fibroblasts (cells in connective tissue).
• Stromal cells (cells in connective tissue).
• Schwann cells (cells that surround neurons).

Various cells can release the same kind of cytokine.

What diseases or conditions involve cytokines?

Cytokines are so essential to your immune system that they play a role in most conditions and diseases that may affect you. Typically, cytokines help keep you infection-free. If your immune system releases too many cytokines — in response to an infection or treatments like immunotherapy — you may develop cytokine release syndrome (CRS), also called a cytokine storm. You may develop various symptoms that affect multiple body systems. CRS can be life-threatening without treatment. Too many cytokines can create a heightened inflammatory response. Too much inflammation can damage tissue and lead to diseases and conditions, including:

• Autoimmune diseases: With autoimmune diseases, your body’s immune cells mistakenly attack healthy cells.
• Metabolic disorders: Metabolic disorders involve problems with metabolism, the process that allows your body to transform food into energy and remove waste from your body.
• Cancer.
• Sepsis: With sepsis, your body’s inflammatory response is so extreme that you experience reduced blood flow to your major organs. Sepsis can be fatal without emergency medical treatment.

Your healthcare provider can prescribe treatments to help reduce inflammation if you have too many cytokines and an overactive immune response.

What is a cytokine panel?

Healthcare providers can determine if your body is producing too many or too few cytokines by using a cytokine panel. A cytokine panel is a blood test that checks your cytokine levels. A healthcare provider draws a blood sample and tests it for cytokines associated with inflammation. Elevated cytokines may be a sign of heightened inflammation, and you may need medication to help.

A note from Cleveland Clinic

Cytokines are essential to having a healthy immune system. As with many things, moderation is key. Having the right amount of cytokines, signaling correctly, can keep you infection-free. High levels of cytokines may lead to excessive inflammation that can be harmful without treatment.